;LEAI
WATER POLLUTION CONTROL RESEARCH SERIES
                                             17030 FEB 02/72
        Fluidic Vortex Bubble  Generator
   U.S. ENVIRONMENTAL PROTECTION AGENCY

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       WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Series describes the
results and progress in the control and abatement of pollution
in our Nation's waters.  They provide a central source of
information on the research, development, and demonstration
activities in the Environmental Protection Agency, through
inhouse research and grants and contracts with Federal,
State and local agencies, research institutions, and
industrial organizations.

Inquiries pertaining to Water Pollution Control Research Reports
should be directed to Chief, Publications Branch, Research
Information Division, Research and Monitoring, Environmental
Protection Agency, Washington, D. C.  20460.

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           FLUIDIC VORTEX BUBBLE GENERATOR
                            by

            BOWLES FLUIDICS CORPORATION
                    9347 Fraser Avenue
              Silver Spring, Maryland 20910
                         for the
          ENVIRONMENTAL PROTECTION AGENCY
               Program Number 17030 FEB
               Contract Number 14-12-863
                     February, 1972
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, B.C. 20402 - Price $1.00

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                 EPA Review Notice
This report has been reviewed by the Environmental
Protection Agency and approved for publication.  Approval
does not signify that the contents necessarily reflect the
views and policies of the Environmental Protection Agency,
nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
                        ii

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                             ABSTRACT
This report contains the results of a detailed engineering investigation
and evaluation of vortex devices as bubble-makers for use in the removal
of suspended solids from wastewaters by flotation.  The specific objective
of the program was the development and test of bubble-makers useful for
generating bubbles having mean diameters of about 100 microns with vortex
devices having minimum liquid passageways of 1/4-inch or greater.  The
overall concept of the program involved testing the feasibility of improved
methods for reducing the cost of generating bubbles for the flotation of
solids from wastewaters.

The results of the program are summarized below:

1.  Bubbles with a mean diameter of 80 to 85 microns, comparable to
    those produced with a pressurized air flotation system, can be
    successfully produced by a vortex bubble-maker.

2.  Data are provided which can be used in the design of a vortex
    bubble-maker.  This bubble-maker can produce bubbles ranging
    in size from 80-85 microns up to 1/8-to 1/4-inch mean diameters;
    with the actual size depending upon liquid pressure and the air
    entrained on the suction side of the pressurizing pump.

3.  The minimum diameter of any internal liquid passageway within
    the device is 1/4 inch for a device having a region of influence
    30 to 36 inches in diameter.

4.  All air consumed by the device is supplied by entrainment at
    atmospheric pressures.  No air compression or regulation is
    required.  Pump pressure needed is 40 psig, which is comparable
    to that used with conventional air flotation systems.

This report was submitted in fulfillment of Project Number 17030 FEB,
Contract 14-12-863, under the sponsorship of the Office of Research
and Monitoring, Environmental Protection Agency.
                                111

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                   TABLE OF CONTENTS




                                                        Page







I      CONCLUSIONS                                       1




II      RECOMMENDATION                                   3




III     INTRODUCTION                                      5




IV     ANALYSIS                                           13




V      DESIGN                                            19




VI     EVALUATION                                        41




VH     FLOTATION TESTING                                 63




VIII    DISCUSSION                                        65




DC     ACKNOWLEDGMENTS                                 67




X      REFERENCES                                        69




XI     PUBLICATIONS AND PATENTS                          73




XII     GLOSSARY                                          75
                              v

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                             FIGURES

                                                             Page

 1   Typical Dissolved Air Flotation Process Equipment            8
       Requirements

 2   Vortex Shedding from a  Submerged Jet                        9

 3   Operating Principle of Vortex Bubble Generator                9

 4   Test Equipment                                           16

 5   Top Vortex Chamber End Cover                             20

 6   Bottom Vortex Chamber  End Cover                          21

 7   Vortex Chamber Housing                                   22

 8   Vortex Chamber Spacers                                   23

 9   Vortex Exit Adapter                                        24

10   Vortex Exit Tubes                                         25

11   Vortex Chamber Spacers                                   26

12   Spacer Number L-2                                        27

13   Adapter and  Single Exit Tube                               27

14   Array of Vortex Exit Tubes                                  28

15   Vortex Bubble-Maker Exploded View                         28

16   Outside Entrainment Adapter Number One                    30

17   Outside Entrainment Adapter Number Two                    31

18   Outside Entrainment Seal Plate                             32

19   Outside Entraining Vortex Exit Tube                         33

20   Modified Exit Tube Hardware for Outside Entrainment         34


                               vii

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                             FIGURES

                                                             Page

21   Photomicrographic Equipment                               36

22   Venturi                                                  37

23   Modified Test Equipment                                  38

24   New Flotation Tank  and Photomicrographic Equipment         39

25   Typical Bubble Photomicrograph Unit L-2-D at 26.9X         46
       Magnification, 36 PSIG

26   Histogram of Bubble Sizes for Vortex Unit No. L-2-D         48

27   Histogram of Bubble Sizes for Pressurized Water System      50
       With Tank

28   Photomicrograph, L-2-J @ 40 PSIG and 0.48 SCIS            52

29   Photomicrograph, L-2-J @ 40 PSIG and 0.48 SCIS            52

30   Photomicrograph, L-2-J @ 40 PSIG and 0.48 SCIS            53

31   Photomicrograph, L-2-J @ 40 PSIG and 0.48 SCIS            53

32   Photomicrograph, L-4-J @ 42.5 PSIG and 0.47 SCIS          54

33   Photomicrograph, L-4-J @ 42.5 PSIG and 0.47 SCIS          54

34   Photomicrograph, L-4-J @ 42.5 PSIG and 0.47 SCIS          55

35   Photomicrograph, L-4-J @ 42.5 PSIG and 0.47 SCIS          55

36   Typical Bubble Dispersion Pattern                          57

37   Photomicrograph, Tankless Pressurization @ 40.5 PSIG       60
       & 0.60 SCIS

38   Photomicrograph, Tankless Pressurization @ 40.5 PSIG       60
       & 0.60 SCIS
                               viii

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                              FIGURES
39   Photomicrograph, Tankless Pressurization @ 40.5 PSIG        61
       & 0.60 SCIS

40   Photomicrograph, Tankless Pressurization @ 40.5 PSIG        61
       & 0.60 SCIS
                                IX

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                              TABLES

                                                               Page
1   Industrial Applications of Dissolved Gas Flotation
     Waste Treatment
2   Vortex Configurations Available for Initial Testing            42


3   Vortex Configurations Selected for Secondary Testing         45


4   Secondary Test Results                                     47


5   Tertiary Test Results                                       51
                                XI

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                           SECTION I

                          CONCLUSIONS
1.  As demonstrated photographically in this program,  the vortex bubble-
maker, as it now exists, can be used to produce bubbles having a mean
diameter of 80 to 85 microns, with virtually all bubbles produced being
130 microns or less in diameter.  This mean size and size range are
substantially the same as bubbles produced by pressurized water processes
at similar operating pressures.

2.  The minimum diameter of any hole used in the best vortex device
tested is one-quarter  inch.  Most holes are considerably larger, and no
moving parts are required.  Therefore, in terms of susceptibility to blockage
and malfunction  in actual use, these devices should perform most reliably.

3.  Bubbles are produced by either of two methods: With atmospheric air
aspirated directly into the vortex unit or with atmospheric air aspirated at
the suction side of the pump, dissolved, and precipitated or effervesced
at the vortex unit.  Of the two methods, the latter gives better results in
terms of numbers of bubbles produced per unit of pumping horsepower.
For either case,  however, no air pressurization equipment is necessary.

4.  The vortex device can be used to produce bubbles  larger than 80 microns
mean diameter merely by increasing the amount of air aspirated  at the unit.
By altering an air valve setting, bubbles having a mean diameter in the range
between  80 microns and 1/4-inch can be generated.

5.  The best vortex device tested produced bubbles at  roughly one-sixth to
one-seventh the rate per horsepower of comparable pressurized  water equip-
ment.  Indications are, however, that this margin may be reduced by in-
creasing vortex gain (obtained by increasing the diameter of the vortex
chamber,  itself)  and by aspirating air to the so-called  "outside" of the
vortex exit cone as well as the "inside".

6.  The region of influence  of a vortex device has  been measured in a
simulated flotation tank.  Bubbles were produced uniformly over a region
roughly 30 to 36  inches by 8 inches in a tank nominally 8 feet long by 8
inches wide by 45 inches in depth, with a device having  a flow rate of
less than 6 gpm  at 40  psig.  Bubbles produced over this region rose to fill
the entire tank length  (eight feet) from a depth of 2-1/2 feet.

7.  Flotation testing was not successfully accomplished with any device
or system during this program, due to test fixture problems.  Sufficient

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data exists, however, to design vortex bubble-makers for direct
functional tests in conventional air flotation systems where a direct
comparison in operating efficiency, reliability, first cost and main-
tenance cost can be made with conventional equipment.

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                            SECTION II

                        RECOMMENDATION
Based on the conclusions resulting from this study, the following recom-
mendation is presented:

Testing to Determine Cost Effectiveness  of Vortex Bubble Generators

It is recommended that a set of vortex bubble generators be tested in a
pilot processing system under conditions which conventional bubble
generators operate.  While not necessary, it would be useful to also
include a control group of conventional generators in the test program.
The pilot operation should simulate a typical flotation process or aeration
process, or, if costs permit, both types  of processes.  The primary ob-
jective  of these tests should be to evaluate the economy of the vortex
generators as compared to conventional equipment.

The complete costs for a system include  (1) initial costs (hardware and
installation),  (2) operating costs (consumables, including  power,  and
labor),  and  (3) maintenance costs  (replacement parts,  labor, and down
time losses).  Regarding initial costs, it is not possible at this time  to
provide exact production costs for the vortex bubble generators, therefore
a good comparison is not possible now.  However, it is felt that there
would be no significant difference between the price of vortex and con-
ventional generators. With either approach, it is expected that the initial
costs amortized over the life of a system, would be far less than the  other
two costs.  Therefore, the study would be primarily directed toward com-
paring the two on the basis of operating and maintenance costs.

For this reason, §n extended period of continuous operation would be
required.  Thus, after the test system with vortex generators is  set up
to yield performance comparable to a  conventional system,  it should be
run for a period of perhaps 3  or 6 months.  It is felt that this period would
yield sufficient data to properly evaluate both operating and maintenance
cost factors for a fair comparison with conventional equipment.

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                          SECTION III

                         INTRODUCTION
DISSOLVED GAS FLOTATION

The interest of the Environmental Protection Agency in improved devices
for gas bubble generation is based upon a long history of use for dissolved
gas flotation processes in industrial and municipal waste treatment.  Ex-
amples of industrial applications are listed in Table 1, which provides
general information on a number of waste materials for which separation
by gas flotation is possible.

As seen in the Table, dissolved gas flotation is an operation by which
solids may be separated from a liquid phase or two or more liquids may be
separated from each other.  Flotation gas  is introduced into the water or
process liquids by a number of techniques.  The choice depends upon a
variety of reasons.  These include the nature of the materials  to be
separated, possible combinations with other processes (sedimentation,
for example),  in-flow and out-flow  concentration limitations,  total flow
requirements, cost limitations,  etcetera.  All the flotation techniques
employed, however, are based on one fundamental process: that of
dissolving a gas at a higher pressure and  subsequent precipitation of
that gas in the form of small bubbles at a  lower pressure.

As reflected in Table 1, the process provides a means for separation
which, for certain wastes, represents the only practical mechanism for
their removal.  This process also provides a mechanism by which sepa-
ration can be achieved in substantially less time and with a markedly
smaller facility than would otherwise be required for settling processes.

The pressure at which gas precipitation occurs will primarily depend
upon the pressure at which the gas was dissolved.  When solution occurs
at atmospheric pressure, for example,  vacuum precipitation is  required.
The pressure in the bubble precipitation tank must be reduced and, inas-
much  as flotation also occurs  in this precipitation tank,  the process  is
called vacuum flotation. When the gas is dissolved at elevated pressures,
precipitation can occur at any lower pressure.  Atmospheric pressure  is
usually selected for such pressure flotation systems.

Assuming the applicability of Henry's Law, which states that the solu-
bility of a gas in equilibrium with a liquid is directly proportional to the
absolute partial pressure of the gas in contact with the liquid, it follows

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                           TABLE 1
            INDUSTRIAL APPLICATIONS OF DISSOLVED
               GAS FLOTATION WASTE TREATMENT
   INDUSTRY
      EXAMPLES OF APPLICATIONS
        OR MATERIALS SEPARATED
Chemical



Food Canneries


Laundries

Meat Packing


Metal Finishing



Metallurgical


Mining


Paper-and Pulp-making


Petroleum


Sugar Refineries


Transporation
Concentration and recovery of fines
  (e.g., carbon, CaSO4,'etc.) and colloids
  (e.g., metals).

Removal of suspended organic solids from
 waste streams.

Recovery of solids and fatty acids.

Recovery of grease and reduction of BOD
  in waste streams.

Removal of suspended chips and processing
  oils from waste  streams.  Recovery of
  certain machining lubricants/coolants.

Removal of oil and scale from mill waste
  streams.

Removal of fines  (e.g., coal dust)  that
  sedimentation cannot separate.

Removal of suspended solids otherwise
  impossible or impractical to separate.

Removal of free or emulsified oils from
  refinery waste streams.

Separation  of impurities and non-sugar
  solids from  raw  sugar melts.

Removal of fine solids and oils  from
  vehicle-washing waste streams.

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that the pressure flotation system is superior to vacuum flotation in
terms of the amount of gas which can be dissolved per unit volume of
water.  Of equal interest  is  the ratio of facilities costs required for
the two types  of systems. The vacuum system can be considerably
more expensive to install than an equivalent pressure system.

Gas flotation can be characterized as a physical process, as opposed
to a chemical  process. Atmospheric air is the cheapest and, therefore,
the best gas available. As  a result,  pressurized air flotation represents
the most popular form for  the fundamental dissolved gas flotation process.

Illustrated in Figure 1  is a block diagram showing the equipment require-
ments for a dissolved air  flotation plant.  Process lines are laid out  to
permit plant operation  by  pressurization of the feedwater or by pressuri-
zation of the recycled  effluent with subsequent mixing  with feedwater
ahead of the flotation tank.  The latter scheme is commonly used when
chemical and biological floe particles are present in the feedwater.

The important  item in Figure 1 is the equipment required for this generalized
system.  The vortex bubble-maker, which was evaluated 'during this  study,
represents a direct replacement for the pressure-regulation valves (usually
flexible-diaphragm types) and the retention tank in effluent recycle appli-
cations.

OPERATION OF THE VORTEX  BUBBLE-MAKER

Gas dissolved or entrained in the liquid is converted into bubbles by in-
jecting the liquid into  the process tank through a nozzle.  To produce
bubbles small enough for  effective flotation (generally 100 microns or less
in diameter), the conventional nozzle must have a relatively small minimum
flow dimension, typically a  few thousandths of an inch.  This requirement
for small nozzles is the source of maintenance problems in operating
systems.  The small nozzles clog  easily and need frequent cleaning.

The vortex bubble-maker produces comparably small bubbles but with a
much larger nozzle.  To understand how this is accomplished it  is appro-
priate to first  consider the properties of submerged water jets and how
bubbles of any size are generated  by simple nozzles.

Figure  2 shows a submerged jet issuing from a nozzle in the presence of
an acoustic disturbance.  The disturbance is assumed to be at the charac-
teristic frequency of the jet, thereby causing vortex shedding.  This
frequency is a function of jet velocity,  diameter and Strouhal Number.   The
Strouhal Number, S = f(d/V),  is substantially constant for turbulent jets
from geometrically similar nozzles.  Thus it can be seen that the frequency

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CD
      ATMOSPHERIC
       AIR
    AIR
COMPRESSOR
                                  PUMP
  PROCESS
  LIQUID
                      RETENTION
                        TANK
  BACK
 PRESSURE
REGULATOR
                                                   FLOTATION
                                                      TANK
                                      *-  FLOAT REMOVAL
                                      -•-  SEDIMENT REMOVAL
                                          CLARIFIED EFFLUENT
                                            FIGURE 1

                               TYPICAL DISSOLVED AIR FLOTATION PROCESS
                                     EQUIPMENT REQUIREMENTS

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      ACOUSTIC DISTURBANCE
        AT BREQUENCY f
WfiTEK
        SINUOUS RESPONSE
           OF JET
                       FIGURE 2

       VORTEX SHEDDING FROM A SUBMERGED JET
                      F IGURE 3

               OPERATING PRINCIPLE OF
             VORTEX BUBBLE GENERATOR

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increases as velocity increases and as diameter decreases.  In practice,
acoustic exitations are always present.  For a highly resonant system
like a submerged turbulent jet, therefore, the shedding of regular vortices
is entirely to be expected.

Under these circumstances if air is permitted to be entrained in the
boundary layer of the submerged liquid jet, it will be broken down into
isolated bubbles by the action of the vortices shedding from the jet.
The higher the frequency of vortex generation, the lower will be the
wavelength between successive vortices and hence-the smaller will be
the air bubbles formed.  In general, smaller bubbles are formed by
increasing the jet velocity and decreasing the jet diameter.

A similar action occurs if, instead of being entrained, the  air is dissolved
in the water issuing from the jet.  In this case,  however,  the air comes
out of solution inside of the individual vortices because these points are
the regions of lowest static  pressure.  Again, the  size of the formed
bubbles is a function of the  frequency of the shed vortices.

Bubbles are  also produced by the same mechanism if the jet is in the  form
of a sheet instead of a circular stream.   Such a jet can be  formed by a
slit shaped  nozzle or by an annular orifice.  Again the bubble size varies
inversely with the frequency of the vortex shedding along the jet.  This
frequency is proportional to  the jet velocity as with a circular jet.  But
in this case, the frequency is also inversely proportional to the width of
the jet stream.  Therefore, to generate small bubbles, less than 100
micron in size, quite narrow jets are required —again in the  order of  a
few thousandths of an inch. As with circular jet nozzles,  this leads  to
maintenance problems because of the tendency for small openings to clog.

The vortex bubble-maker produces a conical sheet jet which, because of its
thinness , can generate small enough bubbles suitable for flotation purposes.
The important advantage of the vortex bubble-maker,  however, is that a
thin jet sheet is achieved with a relatively large nozzle size.

The flow pattern from a vortex bubble generator is  shown in Figure 3.  Here,
water is admitted via a tangentially-directed input pipe into a large central
chamber which  is open at  the bottom to the liquid in which the device is
suspended.  Air can be entrained from the top.  Although the  chamber is
large, the tangential-input-direction forces the entering water to assume a
helical  flow path that is restricted to the outer regions of the chamber.
The rotation continues as  the water flows downward until the chamber ends
whereupon the water continues to flow in a conically-expanding jet.  This
jet can be given the same velocity, thickness and total area  as the jet


                                10

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emanating from a simple annular nozzle thereby producing the same air
bubble size.  Because the jet dimensions are produced by vortex action,
however, no small passageways are required and the vortex device is,
therefore, markedly less susceptible to clogging.

Note that the vortex flow field within the vortex bubble generator is not
to be confused with the vortices shed from the conical jet sheet.  The
latter is the flow phenomenon associated with a jet sheet from any source
by which small air bubbles are produced. The former is the mechanism  by
which the bubble generator produces a  thin jet sheet with a relatively large
exit nozzle dimension.

Note also that the device shown in Figure 3 shows bubbles being generated
from air entrained with the water.  A low pressure exists in the central core
region of the generator which allows air to be aspirated without the need of
an air pump.  This device also produces  bubbles from air dissolved in the
inlet water as described previously for a simple nozzle generator.

PROGRAM ORGANIZATION

The program reported herein was organized on the basis  of preliminary
development work performed by the contractor on the subject  of bubble-
making.  During this preliminary work, the fundamentals of bubble gene-
ration through both freely-entraining and compressed-air-fed vortex
devices were demonstrated.  This  program extends this prior work  in a
systematic way to develop a vortex bubble-generating device suitable for
reliable, low-cost use in flotation-type waste treatment processes.
Specifically, the goals were to develop a device capable of producing
bubbles having a mean diameter as low as or lower than 100 microns
using a simple vortex device in which no liquid passage had  dimensions
smaller than one-quarter inch. The device was to produce these bubbles
with a  minimal expenditure of total energy considering both liquid-and
air-pumping requirements.

The program was organized into four tasks.  These included analysis,
breadboard design,  evaluation and flotation testing.  Section IV of this
report describes the analytical work and  Section V summarizes design
activities,  including both the  design of the devices tested and the equip-
ment used for  such testing.  Evaluation and flotation testing  are covered
in Sections VI  and VII.
                                11

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                            SECTION IV

                             ANALYSIS
The first requirement of the program was the preliminary optimization of
the vortex device in terms  of bubble size and size distribution. This
requirement was based upon the fact that the devices used for earlier
testing had  been selected on the basis of availability rather than for
reasons of optimal size or  capacity.  Hence, a design analysis was
needed to establish the following:

I.  The number and ranges of design variables appropriate for bread-
    boarding .

2.  The size of breadboard units and their scaling in relation to
    requirements of a probable real application.

Practical analysis of bubble formation in vortex motion is  impossible
because of the large number of complex, coupled phenomena  occurring
simultaneously. Some of these phenomena are discussed below:

1.  Coupling  of axial and  radial velocity gradients renders a vortex
    core hydrodynamically unstable,  i.e., tending to produce breakup,
    which makes the core  a spiral of larger area and reduced angular
    velocity.  The breakup  is abrupt and has been described as analogous
    to the well-known hydraulic jump, but the analogy is in  no way exact
    and the phenomenon is not amenable to analysis.  This instability
    applies to the vortex core and is  applicable only indirectly to free
    (or dissolved) air which may be carried along with the core.

2.  Any air  bubble which is entrained within the vortex undergoes an
    axial acceleration from the region of relatively static entrainment
    to the discharge region of the vortex.  This axial acceleration has a
    destabilizing effect on the bubble and has been observed to produce
    breakup of large bubbles into smaller ones.   The result,  a Taylor
    Instability, can produce repetitive breakup of large bubbles into
    smaller ones.

3.  There may be a sharp velocity discontinuity between the  initially
    stagnant air entrained  within the  vortex and the water which
    surrounds it and which is  swirling with very high velocity.  This
    discontinuity would give rise to a Helmholtz  Instability,  which has
    only been studied for laminar,  planar flow.  The superimposed
                                 13

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    centripetal field, however, may actually tend to stabilize any cylin-
    drical air volumes present.

4.  Rayleigh Instability is present,  due partially to a surface tension
    effect,  producing alternate swelling and contraction of a cylindrical
    fluid  column.  Superimposed  rotational motions serve to enhance
    unstable tendencies  in a manner analogous to the instability of an
    elastic  column under the influence of compression combined with
    torque loading.  The result is a  hollow cylindrical column of air
    having superimposed on it surface waves which travel around this
    column  in a helical fashion at high angular velocities.  Coupling
    between these waves and bubble formation has been observed, but
    the phenomenon has  not been described mathematically.

5.  The presence  of a severe radial  pressure gradient has both a
    stabilizing and a destabilizing effect insofar as bubble formation
    is concerned.  As mentioned  above,  the centripetal field tends to
    stabilize cylindrical air volumes and  may, through centrifuging
    action,  also cause bubbles present to coalesce as they travel
    axially  through the exit tube. On the other hand, the low pressures
    produced at the center by this same rotation tend to precipitate air
    (and water vapor) out of solution at the core center in the form of
    small bubbles.  Comparisons of the same vortex bubble-maker
    operated alternately as its own air entrainment unit, as a back-
    pressure regulator for a dissolved air system and as  a  combined
    air entrainer and regulator show  this ambivalence quite clearly.
    These same comparisons also show the ambivalence  to be related
    partially to the gain of the vortex device (the ratio of chamber to
    exit  hole diameters)  at a given pressure, although the  precise
    relationship cannot be ascertained due to the complexity of the
    total  bubble formation process.

6.  The high velocity swirling motion within the water in the vortex core
    region has a destabilizing influence on bubbles or air volumes
    present in this vicinity.  One of the original explanations for the
    behavior of vortex units as bubble-makers, in fact, was  the high
    local vorticity that has been  observed to be present in the boundary
    layers of wake flows.  Unfortunately, this vorticity has only been
    analyzed for flows at Reynolds Numbers in the vicinity of unity and
    below,  versus the four-to five-orders of magnitude larger Reynolds
    Numbers that  prevail in the flow exiting from the vortex devices
    tested in this  program.

In summary, a consideration of factors like those cited above makes it
                                14

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clear that precise analysis of bubble formation in a high-velocity vortex
field is not practicable except under severely restrictive assumptions.
These assumptions so limit the utility of the analysis that the results
have little, if any, physical meaning.

As a result of literature review and prior testing, it was determined that
the two principal variables were the vortex device gain (the ratio of
vortex chamber to exit hole diameters) and water pressure.  Beyond these
two variables, three other geometric characteristics Appeared practical
to vary.  Accordingly, it was decided to provide breadboard capability to
vary four geometric parameters over a broad range.  These geometric
variables included vortex gain, water inlet impedance,  air inlet impedance
and total flow outlet impedance.  The fifth variable was operating water
pressure.  Due to the desirability of minimizing capital cost requirements
in any treatment plant, the air-entraining capabilities of both the vortex
device and the pressurization pump were investigated.  No pressurized
air was used during vortex device tests.

It was necessary to design test equipment which would yield meaningful
results from testing of the vortex devices.  Some means for comparison
testing was considered necessary involving conventional bubble-making
equipment.  Such equipment would provide a basis for direct comparison
of the conventional and the new mechanisms for bubble-making,  as to
bubble size, size distributions, efficiency (bubbles released per unit
horsepower) and flotation effectiveness.  For this purpose, a pressurized
air flotation process was  selected and test equipment was designed
around a dual-purpose laboratory system.

The major components  of the  system are shown in a block diagram in
Figure 4. The system was originally designed to be operated either as
a pressurized dissolved air system or as a non-pressurized system
using the vortex device as a  combined aspirator and bubble-maker.
Bubbles were to be generated in the  flow issuing from the dissolved air
pressurization tank at the back pressure regulator valve, whence they
would pass into the bubble-making and flotation tank for examination
and test  purposes.  Alternatively, bubbles were formed in the vortex
unit  mounted directly in the same bubble-making and flotation tank.
The venturi was a  later addition which provided the option of air entrain-
ment.

Sizing the vortex  device for breadboarding purposes was in a sense related
to pump selection and to the  provision of  a range of both pressures and
flows over which  the breadboard could be operated during  testing.  Based
on the desire for test work at pressures up to 60 psig and variable flow
                                 15

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        WATER
  PRESSURIZED    Q,
  AIR
CD
  ATMOSPHERIC
  AIR
                                DISSOLVED AIR
                                PRESSURIZATION
                                     TANK
                                                   BACK PRESSURE REGULATOR VALVE
                                          VORTEX UNIT
                                                                     BUBBLE-MAKING AND
                                                                       FLOTATION TANK
                                                                   PUMP
           TO
         DRAIN
VENTURI
                                               FIGURE  4
                                             TEST EQUIPMENT

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rates of less than 20 gpm, a centrifugal pump was indicated. A practical
maximum rating for this pump was 1 horsepower, which would permit the
desired flow variations.  Based upon this  pump capacity, the vortex unit
was then sized to permit operation with full pump output pressure at 1/3
or less of maximum pump  flow.
                               17

-------
                            SECTION V

                             DESIGN
This section describes the design and construction of the basic vortex
device to be tested and the test equipment necessary for evaluation.

VORTEX UNIT DESIGN

Design drawings of the basic vortex unit are illustrated in Figures 5
through 10.  The basic design comprises six elements other than O-rings,
hoses, pipe fittings and bolts, screws, nuts and washers.  These
elements are detailed as follows:

1.  Top Vortex Chamber End Cover - Figure 5 -- This is the cover member
    through which air and water are introduced into the device.  It is a
    flat piece of material, 6-inch square by 1/2-inch thick, containing
    eight bolt holes,  two 3/8-inch pipe taps for water admission, one
    3/8-inch pipe tap for a pressure gage, two locating pin holes and
    one 1/4-inch pipe tap through which air may be entrained.

2.  Bottom Vortex  Chamber End Cover - Figure 6 — This is the second
    cover plate and also has overall dimensions of 6-inch by 6-inch by
    1/2-inch, with eight bolt holes and two locating pins. At its center,
    however,  is a 1 1/16-inch diameter through hole to  accommodate
    replaceable exit tubes.

3.  Vortex Chamber Housing  - Figure 7 — The housing is a 6-inch by
    6-inch by 3/4-inch member which, with its 4 3/4-inch diameter
    central  through hole,  is clamped between the end covers where  it
    serves as a high-pressure liquid manifold. The housing contains
    8 bolt holes and two locating pins, and is equipped with an O-ring
    groove on both sides.

4.  Vortex Chamber Spacers - Figure 8 — These spacers,  of which twelve
    were manufactured, were designed with two geometric variables.  The
    variables included overall diameter, both inner and  outer,  and the
    diameter of four tangential holes which were used as high-pressure
    inlets for liquid supplied from the manifold chamber of the vortex
    chamber housing.  The overall diameter changes permitted modifi-
    cations  in vortex gain.  Variations in inlet hole geometry permitted
    independent changes in inlet impedance.   Nominal thickness of the
    spacers was three-fourths of an inch and each was equipped with a
                                19

-------
                             NOTES:
                             1.  REMOVE BURRS AND SHARP-EDGES
                             2.  MATERIAL-.  ACRYLIC SHEET
                             3 .  SPIRAL PINS TO BE LOCATED WITH OPPOSITE
                                 VORTEX CHAMBER END COVER AND VORTEX
                                 CHAMBER HOUSING MATED TO THIS PIECE.
                             4.  DIMENSIONS IN INCHES
             FIGURE 5
TOP VORTEX CHAMBER END COVER

-------
                                                         .266 DIA.
      1.062PIA.
      + .002
      -.000
PEEP.
1.43 4 PIA. BOLT QIRQLE
(FROM OPPOSITE §IP1)  ~~"
(DO NOT PRILL THROUGH)
1/4 DIA. SPIRAL PIN
(SEE NOTE 3).
2 PLACES
                                                         NOTES;
                                                                                          1/2

                                                                                         —.00£
                                                                                        777
                                                                                                     s
                                                                                                     Q
                                                                                                     o
                                                                                                     CM
                                                                                                      si
                                                                                         L*-.016

                                                                                          -.023
                                                         1 .  REMOVE BURRS AND SHARP EDGES
                                                         2.  MATERIAL:  ACRYLIC SHEET
                                                         3 .  SPIRAL PINS TO BE LOCATED WITH
                                                             OPPOSITE VORTEX CHAMBER END
                                                             COVER AND VORTEX CHAMBER HOUSING
                                                             MATED TO THIS PIECE .
                                                         4.  DIMENSIONS IN INCHES
                                                FIGURE 6

                               BOTTOM VORTEX CHAMBER END COVER

-------
                                                                               DRILL.
t\J
                     REAMED HOLE
                     FOR 1/4 DIA.
                     SPIRAL PIN
                     (SEE NOTE » 3)
                     2 PLACES
                                                                                             SECTION A-A

                                                                         NOTES.

                                                                         1. RIMOVl BURRS AND SHARP EDGES
                                                                         a. MATERIAL:  ACRYLIC SHEET
                                                                         3 . SPIRAL PINS TO BE LOCATED WITH VORTEX
                                                                              CHAMBER END COVERS MATES TO THIS PIECE.
                                                                         4.  DIMENSIONS IN INCHES
                                                              FIGURE 7
                                                  VORTEX CHAMBER HOUSING

-------
ITEM
L-l
L-2
L-3
L-4
M-l
M-2
DIA 'A1
3.000
3.000
3.000
3.000
2.500
2.500
DIA 'B1
3.500
3.500
3.500
3.500
3.000
3.000
DIA 'C'
.277
.250
.228
.1935
.277
.250
DIA'D1
3.087
3 .'087
3.087
3.087
2.587
2.587
DIA '£'
3.387
3.387
3.387
3.387
2.887
2.887
DIM'F1
.790
.790
.790
.790
.775
.775
ITEM
M-3
M-4
3-1
3-2
3-3
S-4
DIA 'A'
2.500
2.500
2.000
2.000
2.000
2.000
DIA 'B'
3.000
3.000
2.500
2.500
2.500
2.500
DIA'C'
.228
.1935
.277
.250
.228
.1935
DIA 'D'
2.587
2.587
2.087
2.087
2.087
2.087
DIA'E1
2.887
2.887
2.387
2.387
2.387
2.387
DIM'F1
.775
.775
.760
.760
.760
.760
IS3
GO
                                            DIA.'C'
                                            4 PLACES
                                                   .110
                                                   .114
                                                           375
                                                         SECTION A-A
.110
.114
                                                                             NOTES:

                                                                             1.  REMOVE BURRS AND SHARP EDGES
                                                                             2.  MATERIAL: CAST ACRYLIC TUBE
                                                                             3.  DIAS. 'A1 and 'B' TO BE TOLERANCED
                                                                                  AS RECEIVED.
                                                                             4.  DIMENSIONS IN INCHES
                                                            FIGURE 8
                                                  VORTEX CHAMBER SPACERS

-------
                                                        .177 DIA.. 3 PLACES
                                                        EQUALLY SPACED ON
                                                        1.434 DIA. BOLT CIRCLE
(S3
                                                                       _L
                                                                       32
                   No. 10-24UNC-2B TAP/««
                   3 PLACES EQUALLY SPACED
                   ON 2.125 DIA. BOLT CIRCLE
1. REMOVE BURRS AND SHARP EDGES.
2. MATERIAL: ACRYLIC TUBE/ROD.
3 . DIMENSIONS IN INCHES
                                                                                                      No. 8-32UNC-2BTAP
                                                            FIGURE  9
                                                    VORTEX EXIT ADAPTER

-------
ITEM
A
B
C
D
E
F
DIM'L1
1.50
1.50
2.50
3.50
3.50
6,00
DIA.'A'
.50
.75
.71
.SO
.75
,10
ITEM
G
H
I
J
DIM'L'
6.00
12.00
12.00
1.50
DIA.'A1
.75
.50
.75
.25
                                                                 •(-.005
to
01
                                                                                     •DIA. 'B'
                                                                                       I	DIA. 'C'
                                                                           NOTES;
                                                                           1
                                                                           2
                                                                           3
                                                                           4
REMOVE BURRS AND SHARP EDGES
MATERIAL: CAST ACRYLIC TUBE/ROD
OD TO BE TOLERANCED AS RECEIVED
DIAS.'B1  & 'C' CONCENTRIC WITHIN
                                                                           5.
  .005 TIR
DIMENSIONS IN INCHES
                                                            FIGURE  10

                                                        VORTEX EXIT TUBES

-------
    pair of O-rings for clamping and sealing between the vortex end
    covers.

5.  Vortex Exit Adapter - Figure 9 — The adapter is a single transition
    member used to hold the vortex exit tube securely in a central hole
    within the bottom end cover.

6.  Vortex Exit Tubes - Figure 10 — Ten exit tubes of different sizes
    were designed and fabricated.  This array permitted relatively in-
    dependent variation of vortex gain  (dependent upon exit hole
    diameter) and outlet  impedance (dependent upon exit hole diameter
    and length).  As shown in Figure 10, each exit tube contains an O-
    ring groove used to seal it in position within the vortex device. A
    set screw in the adapter is  employed to assure that the tube remains
    stably seated.

Figures 11 and 12 Illustrate twelve vortex chamber spacers and a closeup
view of one  design (L-2), respectively.  Figure 13 is a photograph of the
vortex exit adapter together with one of the exit tubes.  The complete
array  of exit tubes is shown in Figure 14.

Figure 15 is a photograph of the vortex bubble-maker set up as an exploded
                              FIGURE 11

                       VORTEX CHAMBER SPACERS

                                26

-------
         FIGURE 12
     SPACER NUMBER L-2
         FIGURE 13
ADAPTER AND SINGLE EXIT TUBE
             27

-------
              FIGURE 14
     ARRAY OF VORTEX EXIT TUBES
              FIGURE 15
VORTEX BUBBLE-MAKER EXPLODED VIEW
                 28

-------
view.  At the left, the top end cover (see Figure 5)  is shown with high-
pressure liquid lines and a pressure gage attached.  Also attached to
the top end cover is the housing (see Figure 6), which is held in position
in this photograph by friction at the locating pins.  The right side of the
figure  shows one of the large (L-series) chamber spacers followed by the
bottom cover plate, the adapter, and the D-coded (3-1/2-inch long by
1/2-inch ID) exit tube. Also shown is the hardware used to assemble the
device. Although not readily apparent in the photograph, all O-rings are
in place  on this unit.  Most of the material selected for construction was
acrylic plastic. The reason for this selection was to permit observation
of the  flow internal to the unit.  All of the test tanks were also constructed
of this material to permit easy visualization and photography.

In addition to the basic design outlined above,  one other objective also
required evaluation work and necessitated special design.  This objective
was an exploration of the possibility for doubling the bubble-making
capacity of the fundamental device by permitting air to be entrained both
at the  "inside" and "outside"  of the device.  The terms "inside" and
"outside" refer to the conical  sheet of high-velocity swirling fluid which
exits from an operating vortex bubble-maker. This  sheet has an inside
surface and an outside surface. The hardware shown in Figure 15 per-
mitted air entrainment  and distribution only to the inside surface of the
cone.  Additional hardware was needed to permit entrainment at  the outside
surface simultaneously.

Figures 16 through 19 are detailed drawings of the two basic devices used
to evaluate this concept.  As shown in Figure 19, an adaptation of the
fundamental vortex exit tube design was necessary. The modification
comprises a necking down of the portion of the tube which protrudes from
the vortex exit adapter.  This  necked-down portion  fits  within the central
holes of  the adapters  shown in Figures  16 and 17.   These designs gave
the option of operating with the outside of the vortex cone either vented
or non-vented to the atmosphere.  Both entrainment adapters were fitted
with holes which permitted them to be stabilized with any degree of  axial
insertion of the exit tube from full to zero.  Figure  20 illustrates the modi-
fied exit tube,  together with adapter number one and its associated seal
plate.  As shown in the figure, the adapter is equipped with a fitting
through which air can be admitted.

TEST EQUIPMENT DESIGN

Three fundamental types of test equipment were required for this program.
Two of these types involved plumbing and tanks for bubble-making evaluation
and flotation testing.  The third involved photographic equipment and lighting
suitable  for high-definition photomicrographs of the bubbles formed.

                                 29

-------
                                      1-3/4-16 UN
-2B 0
1/4 DIA. EMD
MILLX
1/8 (MAX}
DEEP
3 PLACES
                                                             -.201 DIA. THROUGH
                                                               3 PLACES
                                                         MO.HI1I-24-UMC-2B TAP.
                                                         3 PLACES EQUALLY SPACED
                                              3.
                                              4.
  MATERIAL:  ACRYLIC
  DIAS. CONCENTRIC WIT]
   EXCEPT THOSE WITH
   CONCENTRIC WITHIN
  BREAK EDGES .010 R MAX.
  DIMENSIONS IN INCHES
                                                                        .010 TIR
                                                                        , TO BE
                                                                      12 TIR.
                                     FIGURE 16
                    OUTSIDE ENTRMNMENT ADAPTER NUMBER ONE
                                          30

-------
1-3/4-16UN-2B
O-RING   _
GROOVE,
.054 ± .002
DEEPX .094
WIDE  >V)
  rm o
  o o
  oo
  + I
   CM
 (7)  .500


      1/4
                                                    ©
                                                              ..201 DIA. THROUGH,
                                                              3 PLACES
                                                          No. 10-24 UNC-2B TAP.
                                                          3 PLACES EQUALLY SPACED
                                          1. MATERIAL: ACRYLIC
                                          2. D1AS. CONCENTRIC WITHM .010) TO EXCEPT
                                               THOSE WITH f*j , TO BE CQWCENTRIC

                                          3 . BRE9SC EDGES . OHIO R WffiiK.
                                       FIGURE  17

                     OUTSIDE ENTRAINMENT  ADAPTER NUMBER TWO
                                            31

-------
                      1/4.

                                         1-3/4-16 UN-2A
                   (MAX.)
             1-1/16
             DLA.
                       — A —
         .375
         DIA.

                                               1-3/8 DIA.
                                             1/8 DRILL x 1/16 DEEP,
                                             2 PLACES 180° APART
11A .002 TIR
                                    .126+ .002
NOTES:

1. MAKE:  2
2. MATERIAL: ACRYLIC
3. DIAS. CONCENTRIC WITHIN .010 TIR
4. BREAK EDGES  .010 R MAX.
5. DIMENSIONS  IN INCHES
                          FIGURE 18

             OUTSIDE ENTRAINMENT SEAL PLATE
                            31821
                              32

-------
00
CO
                                                                	 .500
                                                                        DIA 'C'
                                                                             1/4 DIA. THROUGH
                                                   NOTES;
                                                   1.  REMOVE BURRS AND SHARP EDGES
                                                   2.  MATERIAL:  ACRYLIC TUBE/ROD, 1-1/4 OD
                                                   3 .  OD TO BE TOLERANCED AS RECEIVED
                                                   4.  BURNISH FOR O-RING SEAL
                                                   5.  DIAS.'A1, -B1, and 'C1 CONCENTRIC WITHIN
                                                        .005 TIR
                                                   6.  DIMENSIONS IN INCHES
                                               FIGURE 19

                                  OUTSIDE ENTRAINING VORTEX EXIT TUBE
                                                                                         31822

-------
                            FIGURE 20

                MODIFIED EXIT TUBE HARDWARE FOR
                       OUTSIDE ENTRAINMENT
Photographic Equipment

After some experimentation,  a Nikon binocular microscope was found to
be suitable as the basic image-formation device.  Coupled with Nikon
Microflex photographic equipment and a Polaroid sheet film adapter, the
microscope was capable of linear photographic magnifications of 26.9X
(with  10X eyepieces) and 53.8X (with 20X eyepieces).  The microscope's
focal  point was situated roughly 1-1/2 inches from the objective lens,
which permitted easy focusing on locations well inside any of the test
tanks.

One of the major photographic problems which had to be solved was  in
the area  of lighting. Using continuous lighting, very fast shutter speeds
were necessary to "stop" the moving bubbles.  At such speeds, no position
of the lights was  possible which would provide both a visible image of the
bubbles and yield enough illumination to give a visible record of that image
on film,  in spite of  the fact that Type 57 Polaroid film having a speed of
3000  (ASA equivalent) was used.

Accordingly, emphasis was transferred to a flash lighting technique


                                34

-------
utilizing very intense lighting with a duration of a small fraction of a
second.  Various light sources,  ranging from a  Braun Hobby 200 minia-
ture photoflash unit to an EG&G  Model 502 Multiple Microflash unit,
were tested.  The former had an  excessive exposure duration (approxi-
mately 100 microseconds).  The  latter unit permits control of the time
intervals between successive flashes from 40 milliseconds to 10 micro-
seconds .  The unit is equippped with a high intensity flash  lamp whose
power pulse has a duration of 1 microsecond.  Unfortunately,  this
appeared to be too short for effective exposure.

The ideal flash lighting source was found to be a portable stroboscopic
unit, the Strobonar, produced by the Heiland Division of Honeywell.
The strobe  flash has a reasonably  short duration, with an intensity
adequate for proper illumination  of the bubbles. Appropriate lighting
positions were developed to yield  effective microphotographs .  At 53.8X
magnifications,  bubbles having a diameter less than 5 microns could
easily be seen and sized in the photographs. Assuming that a bubble
photograph as small as 0.010 inch in diameter could be easily resolved,
a magnification of SOX would yield the capability of discerning bubbles
as small as 5 microns  in diameter.

Since 10-micron resolution was subsequently found to be adequate for
the actual sizes of bubbles present, 25X magnification was  used.  This
had the advantage that each photograph showed four times as many
bubbles, thus giving a much more  adequate representation of bubble size
distribution than was  possible with the higher magnification. With an
actual magnification factor of 26.9X, each 3-1/2-inch by 4-l/2~inch
photograph had a total field of view of 0.130 x  0.167  inches .  Measure-
ment resolution to 0.01 inches (approximately 9.5 microns)  on these
photographs was achieved with a 1:100 inch scale.

The Nikon and Honeywell equipment in position is shown in Figure 21.
As indicated in the figure, reflected lighting  against a black back-drop
(the small rectangular object partially hidden behind the Strobonar unit)
was used.

Bubble-Making and Flotation Test  Equipment

The initial  testing concept visualized for the program called for dual-
purpose test equipment. As outlined in the block diagram of Figure 4,
the original system was to have  two different bubble sources, either of
which would discharge into the bubble-making and flotation tank.  A
description  of the original system  is as  follows:
                                 35

-------
                            FIGURE 21

                PHOTOMICROGRAPHIC EQUIPMENT


1.  The dissolved-alr pressurization tank was an acrylic cylinder
    (10-Inch ID, 11-Inch OD and 53  inches in length) sealed at both
    ends, with internal baffling to permit efficient gas transfer.  The
    tank was equipped with a short drain line to a one-inch gate valve
    that served as a back pressure regulator.

2.  The bubble-making and flotation tank was an acrylic cylinder
    (9.75-inch ID, 10-inch OD and 53 inches in length) sealed at one
    end, with an inlet from the dissolved air pressurization tank via
    the back pressure regulator valve and a water outlet via a 1-1/4-
    inch pipe and gate valve.

3.  The pump was  a Sears, Roebuck Deluxe Convertible Deep Well Jet
    Pump with a shallow well jet attachment, Model 390.25931, with
    a 1-horsepower drive motor.

4.  The piping and valves consisted of one-inch pressure lines, 1-1/4-
    inch suction lines, flexible PVC pipe and bronze gate valves.

5.  The air pressure regulator was a Falrchild-Hiller Kendall Model 30
    pressure regulator.
                                36

-------
6.   The aspirator was a specially-designed venturi unit for entrainment
     of atmospheric air at the suction side of the pump, as  shown in
     Figure 22.
                             FIGURE 22

                              VENTURI

In the initial testing of the vortex device as a bubble-maker, this test
equipment proved entirely adequate.  However, the bubble-making tank
lacked sufficient volume for a demonstration of the dispersion character-
istics of bubbles formed by any of the bubble-makers.  Moreover,  success-
ful use of the same relatively small tank for both floe generation and bubble-
making during flotation tests was not possible.  Hence, the test equipment
as originally designed was modified to the configuration shown in the block
diagram of Figure 23.  In an effort to overcome the flotation problem, the
floe generation function was  separated from those  of bubble formation and
flotation. Specifically, the test equipment now  included a separate new
bubble-making and flotation tank that was nominally eight feet long by
four feet high by 2/3-foot wide. The tank was designed so that inputs
from any of three bubble sources (vortex, tank-pressurized water,  and
tankless pressurized water) might be introduced  at one end.  Also at this
end, floe mixtures from a  separate mixing and flocculation tank could be
introduced at variable flow rates up to 10 gpm.  At its opposite end,  the
tank was equipped with a  high weir for draining of floated material and
with a low drain from which effluent could be removed by pumping.  The
                                37

-------
CO
00
      Water
       Pressurized
       Air   o	
   Atmospheric
   Air      °-
    Water
                  <>•&-
                           Pressurization
                                Tank
A12(SOJ3
 Solution
      Mixing and
   Flocculating Tank
   Bubble-making and
     Flotation Tank
                                                                                             Turbidity
                                                                                             Test
                                                                                             ^To Drain
                                                FIGURE 23

                                        MODIFIED TEST EQUIPMENT
                                                                                                31823

-------
 new tank and some of the photomicrographic equipment are shown in
 Figure 24.
                             FIGURE 24

     NEW FLOTATION TANK AND PHOTOMICROGRAPHIC EQUIPMENT


The original flotation tank was converted to a mixing and flocculation
tank.  The water, after dosing with bentonite and alum, was stirred
with a variable speed apparatus capable of rotation at rates as low as
20 rpm.  The flocculated tapwater could then be introduced to the bubble
making and flotation tank at variable rates that were not dependent upon
any pumping action.

Jar tests were performed to determine the optimum dose of aluminum
sulfate solution for clarification of the tapwater seeded with 50mg/l
of bentonite.  Because local water is quite soft,  a dose of 25 milligrams
of aluminum sulfate per liter was found to be optimum.

It was determined that turbidity measurements would provide the best
means for assessing the relative effectiveness of the flotation tests.
                               39

-------
For this purpose, a Hach Model 2100A Laboratory Turbidimeter,capable
of measurements from O-to-1000 Jackson Turbidity Units  (ITU), was
purchased to permit quantitative determination of flotation efficiency.
                               40

-------
                           SECTION VI

                           EVALUATION
The evaluation of the vortex devices as bubble generators was performed
in three stages. Each vortex configuration was operated over a range of
water pressures  and air flow rates.  Those configurations exhibiting maxi-
mum performance in terms of numbers of bubbles produced in a given size
range per unit horsepower were then selected for further evaluation. Such
further evaluation was designed to study the effects of chamber geometry
and operation at various chamber depths.

INITIAL TEST STAGE

During initial testing,  emphasis was placed on the relative operability of
the various devices.  At this  early stage, sixty vortex geometric combi-
nations, shown in Table 2, were available. The first objective, therefore,
was to reduce this  large quantity to a lesser number, more suitable for
detailed testing. In this first test, each configuration was pressurized
to 10  psig and 20 psig, successively, and a determination was made as
to two characteristics:

              1. Atmospheric air entrainment capability.

              2. Minimum bubble size produced.

First, all sixty configurations developed  vacuum in their vortex cores
sufficient to  entrain atmospheric air without the need for a separate
compressed air line.  Prior to program startup, certain other vortex
devices had required positive pressurization in order to develop any
bubbles.

Second,  there was an easily observed gradation in the minimum sizes of
bubbles produced.  The gradation varied with pressure, i.e. , minimum
bubble sizes  generally appeared at maximum pressure.  The major effect
of pressure,  however,  was in the quantity of bubbles produced in any
given size range:  More bubbles were generally produced at higher
operating pressures.  This is consistent with the fundamental concept
of how bubbles are  formed in the vortex discharge flow. An even more
important part of this second observation, however, was the fact that
maximum performance at any given pressure appeared to be related to
geometry.  Smaller  bubbles, and more of them,  tended to be produced
by configurations having larger vortex diameters (L-units) and  smaller
exit tube ID'S (-A and -D  units) .

                                41

-------
             TABLE 2

VORTEX CONFIGURATIONS AVAILABLE
       FOR INITIAL TESTING
DESIG-
NATION
L-l-A
L-l-B
L-l-C
L-l-D
L-l-E
L-2-A
L-2-B
L-2-C
L-2-D
L-2-E
L-3-A
L-3-B
L-3-C
L-3-D
L-3-E
L-4-A
L-4-B
L-4-C
L-4-D
L-4-E
M-l-A
M-l-B
M-l-C
M-l-D
M-l-E
M-2-A
M-2-B
M-2-C
M-2-D
M-2-E
CHAMBER
OD
INCHES
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
CHAMBER INLET
HOLE DIAMETER
INCHES
0.277
0.277
0.277
0.277
0.277
0.250
0.250
0.250
0.250
0.250
0.228
0.228
0.228
0.228
0.228
0.1935
0.1935
0.1935
0.1935
0.1935
0.277
0.277
0.277
0.277
0.277
0.250
0.250
0.250
0.250
0.250
EXIT TUBE
INNER
DIAMETER
INCHES
0.50
0.75
0.75
0.50
0.75
0.50
0.75
0.75
0.50
0.75
0.50
0.75
0.75
0.50
0.75
0.50
0.75
0.75
0.50
0.75
0.50
0.75
0.75
0.50
0.75
0.50
0.75
0.75
0.50
0.75
EXIT TUBE
LENGTH, INCHES
1.5
1.5
2.5
3.5
3.5
1.5
1.5
2.5
3.5
3.5
1.5
1.5
2.5
3.5
3.5
1.5
1.5
2.5
3.5
3.5
1.5
1.5
2.5
3.5
3.5
1.5
1.5
2.5
3.5
3.5
              42

-------
TABLE 2  (CONTINUED)
DESIG-
NATION
M-3-A
M-3-B
M-3-C
M-3-D
M-3-E
M-4-A
M-4-B
M-4-C
M-4-D
M-4-E
S-l-A
S-l-B
S-l-C
S-l-D
S-l-E
S-2-A
S-2-B
S-2-C
S-2-D
S-2-E
S-3-A
S-3-R
S-3-C
S-3-D
S-3-E
S-4-A
S-4-B
S-4-C
S-4-D
S-4-E
CHAMBER
OD
INCHES
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
CHAMBER INLET
HOLE DIAMETER
INCHES
0.228
0.228
0.228
0.228
0.228
0.1935
0.1935
0.1935
0.1935
0.1935
0.277
0.277
0.277
0.277
0.277
0.250
0.250
0.250
0.250
0.250
0.228
0.228
0.228
0.228
0.228
0.1935
0.1935
0.1935
0.1935
0.1935
EXIT TUBE
INNER
DIAMETER
INCHES
0.50
0.75
0.75
0.50
0.75
0.50
0.75
0.75
0.50
0.75
0.50
0.75
0.75
0.50
0.75
0.50
0.75
0.75
0.50
0.75
0.50
0.75
0.75
0.50
0.75
0.50
0.75
0.75
0.50
0.75
EXIT TUBE
LENGTH, INCHES
1.5
1.5
2.5
3.5
3.5
1.5
1.5
2.5
3.5
3.5
1.5
1.5
2.5
3.5
3.5
1.5
1.5
2.5
3.5
3.5
1.5
1.5
2.5
3.5
3.5
1.5
1.5
2.5
3.5
3.5
       43

-------
SECONDARY TEST STAGE

It should be noted that these tests were in the nature of a coarse
screening.  Photography was concurrently attempted, but without
successful high-resolution results.  Moreover, the limited flow
capacity of the pumps at high pressure made it impossible to obtain
comparable data for all  configurations at all conditions of operation.
For example, data for the relatively high-impedance configurations
could be obtained at operating liquid pressures as high as 28 psig.
For the lower-impedance units such as S-l-B  and S-l-D,  however,
testing was  limited to pressures of 20 psig and below.  Accordingly,
the evaluation up to this point was somewhat  subjective.

The initial tests were all performed with pumps of limited capacity and
without the availability of a useful photographic technique.  As a  re-
sult,  while it was obvious that no advantage lay in retention of mid-
range sizes  of vortex configurations  (e.g. , M- units  and -C units) ,
there  was sufficient question  as to the relative importance of vortex
gain versus  vortex inlet and outlet impedance to warrant continuing
the relative  evaluation of L- and S- units  at higher  operating pressures.
Accordingly, some sixteen of  the configurations listed in Table 2 were
selected for such continued  testing.  These sixteen are listed in Table 3.

Secondary testing utilized the test setup described  in Figure 4.  Also,
development of the final photographic technique and lighting arrangements
had progressed so that a quantitatively recorded evaluation could  be made.

The secondary evaluation phase of testing comprised  operation over a
range of pressures with photography of the bubbles  formed at each of the
operating  pressures.  Each of the configurations listed in Table 3 was
operated at pressures of 10, 20 and 30 psig, and some of them were
operated at pressures as high as 40 psig.  At  each of these pressures,
photographic calibration of bubble output was made, with photographs
like the one shown in Figure 25.  Several  photographs were taken  for
each configuration at each operating condition.  Each photograph was
then examined and the diameters of all bubbles in focus were individually
measured  to a resolution of 0.01 inch on the  photograph, which was
adjudged adequate for the bubble sizes actually present.

At this time,  it had become apparent that there was actually a choice of
operating  methods for the  basic vortex device. The device could be
operated as  its own air entrainer or aspirator, or it  could be operated as a
back pressure regulation device with air being supplied via the pump.   The
basic technique for the  latter  method has been worked out with a crude
aspiration device on the earlier pumps.

                                44

-------
                               TABLE 3

                  VORTEX CONFIGURATIONS SELECTED
                       FOR SECONDARY TESTING
DESIG-
NATION
L-2-A
L-2-B
L-2-D
L-2-E
L-4-A
L-4-B
L-4-D
L-4-E
S-2-A
S-2-B
S-2-D
S-2-E
S-4-A
S-4-B
S-4-D
S-4-E
CHAMBER
OD
INCHES
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
CHAMBER INLET
HOLE DIAMETER
INCHES
0.250
0.250
0.250
0.250
0.1935
0.1935
0.1935
0.1935
0.250
0.250
0.250
0.250
0.1935
0.1935
0.1935
0.1935
EXIT TUBE
INNER
DIAMETER
INCHES
0.50
0.75
0.50
0.75
0.50
0.75
0.50
0.75
0.50
0.75
0.50
0.75
0.50
0.75
0.50
0.75
EXIT TUBE
LENGTH, INCHES
1.5
1.5
3.5
3.5
1.5
1.5
3.5
3.5
1.5
1.5
3.5
3.5
1.5
1.5
3.5
3.5
For this round of testing the venturi shown in Figure 22 was designed and
built.  A direct comparison with operation of each vortex configuration in
each of these two modes clearly showed the superiority of air entrainment
and pressurization via the pump over air entrainment in the vortex itself.
This is understandable inasmuch as the amount of air in solution at the high
output pressure of the pump is considerably greater than that entrained at
the reduced pressure in the vortex core.  The margin of superiority in terms
of numbers of bubbles of a given size range per photograph averaged approxi-
mately two-to-one for pump entrainment over vortex entrainment.  Hence,
from this point forward, all further vortex  measurements were made with the
"inside" air supplied by the venturi located at the  suction side of the pump.

Results for the second-round tests are summarized in Table 4.  The more
promising performance levels are  underlined.  Considering the ranges of
                                 45

-------
                           FIGURE 25

              TYPICAL BUBBLE PHOTOMICROGRAPH
          UNIT L-2-D AT 26.9X MAGNIFICATION,  36 PSIG

parameters over which tests were conducted, the results in terms of both
bubble sizes and number of bubbles produced"per unit volume were quite
flat, with mean bubble size varying over a range from approximately
85)ji to 120 |i .  Not surprising  was the superiority of the larger vortex
units (Code  L) over the smaller ones (Code S) in producing small bubbles,
but the margin of superiority was lower than anticipated and data were
scattered. Likewise, smaller bubbles were usually obtained at higher
operating  pressures,  but again data showed scatter.  The scatter in the
data was due to the fact that local  bubble velocity  in some photographs
was  clearly  higher than in others, making accurate  measurements more
difficult.

In general, the better combination of vortex geometry and pressures
yielded very similar results in terms of small bubble size (around 85
microns diameter). In terms of the number of bubbles produced per unit
volume of water in the bubble-making tank, the number of countable
bubbles shows a considerable spread.  The spread  amounts to more than
3 to  1 between the maximum and mean numbers for the approximately 100
photographs taken.  However, for those photographs exhibiting a mean
bubble diameter of 90 microns or less,  the mean bubble count is roughly
20%  higher than that  of the entire array. Data  in the  form of a histogram
for the best  configuration are  given in Figure 26.

                               46

-------
                                  TABLE 4
                          SECONDARY TEST RESULTS
VORTEX
DESIG-
NATION
L-2-A
L-2-B
L-2-D
L-2-E
L-4-A
L-4-B
L-4-D
L-4-E
S-2-A
S-2-B
S-2-D
S-2-E
S-4-A
S-4-B
S-4-D
S-4-E
20 PSIG
MEAN
BUBBLE
DIAMETER
MICRONS
118
97
94
89
90
*
100
91
85
*
*
110
*
9£
*
99
BUBBLES/
HORSE-
POWER
.616,
432
381
342
854
*
644
230
685
*
*
376
*
360
*
632
30 PSIG
MEAN
BUBBLE
DIAMETER
MICRONS
112
*
103
*
84
104
86.
110
106
*
*
88.
iL
*
*
105
BUBBLES/
HORSE-
POWER
510
*
389
*
447
432
461
369
565
*
*
166
534
*
*
320
40 PSIG
MEAN
BUBBLE
DIAMETER
MICRONS
***
***
86 **
***
84
94
96
103
***
***
***
***
***
***
***
***
BUBBLES/
HORSE-
POWER
***
***
758 **
***
616
288
566
187
***
***
***
***
***
***
***
***
* Unsatisfactory bubble size or concentration
** 36 PSIG
*** Inoperable or unsatisfactory bubble concentration.
                                   47

-------
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   40
   35
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   25
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     CT)

     OO
                        OPERATION AT 36 PSIG
                        MICROSCOPE/CAMERA
                        MAGNIFICATION FACTOR
                          26.9
                        MEAN = 86 MICRONS
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-------
In order to get comparative data between the performance of the vortex
device and a more conventional system,  the pressurization fixture was
operated and produced the histogram shown in Figure 27.  The data are
not significantly different from that of Figure 26. The main point is,
however,  that the  data tend to confirm the relationship between minimum
bubble size and pressure:  Mean bubble size from this  entirely different
process was roughly 80 microns and the histogram shows a scatter similar
to that of Figure 26.  In terms of a subjective evaluation, both aerated
containers of water were milky but that of Figure 27 was considerably
milkier than that of Figure 26 .  The bubble count for Figure 27 was ,
however,  only 35% higher than that for Figure 26.

Based upon the scatter in the data shown in Table 4, some of the tests
required repetition under conditions more favorable for  the necessary
photographic work. As observed previously, local bubble velocities in
certain of the photographs were higher than in others, sometimes making
accurate measurements impossible.  A considerable portion of the prob-
lem lay in the fixturization: Specifically, in the combined bubble-making
and flotation tank. This tank was too small for many of the tests, as
demonstrated by the relatively high turbulent velocities with which bubbles
would intermittently swirl through the camera field of view.  In addition,
this tank was too small for measurements of the  dispersion of bubbles
formed by any of the techniques and devices available. Hence,  the test
equipment modifications  described in Section Vwere introduced for all
further testing.

TERTIARY TEST STAGE

The first requirement  in the third stage of testing was to determine whether
further improvement in vortex bubble generator performance (i.e., that
aspect of performance relating quantity of bubbles  produced per unit of
water pumped) might be obtained by increasing the output impedance
of the device alone or whether a change in vortex gain  (i.e., the ratio
of inlet to outlet diameters)  was the primary factor. For this purpose,
four additional vortex exit tubes (-F, -G, -H and -I in Figure 10) were
built and tested, each one consisting of  a hollow cylinder designed to be
inserted into the basic vortex device.  Each cylinder had an inner diameter
of either 1/2 or 3/4-inch and was identical to the existing outlets except
for overall length.  Values for this dimension of  6 and  12 inches  were
used, versus the 1-1/2- and 3-1/2-inch values  selected previously.
Selection  of length alone as the means of modifying impedance was
based upon the fact that  a change in the  diameter of the outlet hole
would change both impedance  and gain.  A change in length  alone was,
therefore, the easiest means for checking the  effect of impedance in-
dependent of gain.

                                49

-------
H
O
0
w
   40
  35
  30
   25
   20
w  . _
a,  15
   10
OPERATION AT 40 PSIG
MICROSCOPE/CAMERA
MAGNIFICATION FACTOR
  26.9
MEAN = 79 MICRONS
         CO
             BUBBLE DIAMETER,  MICRONS
             FIGURE 27

      HISTOGRAM OF BUBBLE SIZES
        FOR PRESSURIZED WATER
           SYSTEM WITH TANK
                                           31825
                50

-------
The vortex unit, equipped with these new outlets, was restested, and
results were compared with those obtained from earlier tests.  With the
longer exit tubes, the small changes in performance noted previously
between, for example, L-4-A and L-4-D became much more evident.  A
visibly greater number of bubbles was produced per unit volume of water
using the shorter outlet  nozzles.  Also, cross-comparison of performance
between long and short outlet nozzles of the two inside diameters shows
that performance is definitely improved with smaller nozzle ID. This,
coupled with earlier observations of better performance in terms of bubble
size with large values of the vortex diameter, indicates that vortex gain
is a major factor in establishing total performance of the vortex device.
To confirm  this finding,  a comparative test was made between  some of the
original vortex units and similar units incorporating modified gains. For
this purpose,  a new exit tube arrangement (-J in Figure 10) was designed,
built, and tested.  This arrangement provided a reduced ID  (1/4-inch)
exit for the vortex flow, while length was maintained at 1-1/2  inches.
Tests  were run with the two nozzles using the same four vortex rings
that had been  subjected to previous tests.  The tests were performed in
the new flotation tank, and four photographs were taken for each of the
configurations. Water flow rate and delivery pressure were also recorded
for each.  Data are given in Table 5.  Photographs for the best two
combinations are shown in Figures 28  through 35.

                           TABLE 5

                    TERTIARY TEST RESULTS



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                               51

-------
                  FIGURE 28
PHOTOMICROGRAPH, L-2-J @ 40 PSIG and 0.48 SCIS
                  FIGURE 29
PHOTOMICROGRAPH, L-2-J @ 40 PSIG and 0.48 SCIS
                     52

-------
                   FIGURE 30
PHOTOMICROGRAPH, L-2-J @ 40 PSIG and 0.48 SCIS
                                     '-"  100ML
                  FIGURE 31
PHOTOMICROGRAPH, L-2-J @ 40 PSIG and 0.48 SCIS
                      53

-------
                  FIGURE 32
PHOTOMICROGRAPH, L-4-J @ 42.5 PSIG and 0.47 SCIS
                  FIGURE 33
PHOTOMICROGRAPH, L-4-J @ 42.5 PSIG and 0.47 SCIS

                     54

-------
                  FIGURE 34
PHOTOMICROGRAPH, L-4-J @ 42.5 PSIG and 0.47 SCIS
                  FIGURE 35
PHOTOMICROGRAPH, L-4-J @ 42.5 PSIG and 0.47 SCIS
                     55

-------
Small bubble diameters ,  high numbers of bubbles photographed and high
values of bubbles  photographed per input horsepower were the evaluation
parameters.  The better data are underlined in the table.  From the table,
bubble sizes are roughly the same for the large and small group of vortex
units, with an increase in bubble diameter occurring as one goes from a
low to a high input impedance device (e.g. , L-2-A  to L-4-A or S-2-J  to
S-4-J) .   In terms of bubble size alone, there is relatively little to choose
between units having a mean output of 80 and  90  microns.  The major
point of comparison is,  therefore, the number  of bubbles produced and the
power expended in producing them.  The L-units , with.their high gain, are
generally superior to the S-units and, within each size category, the high-
gain-J units are generally superior to the -A units.

The L-2-J configuration operating at  40 psi is  judged to have the best per-
formance.  It is the only configuration which yielded a high relative bubble
count, had a relatively high bubble-per-horsepower gain, and produced
bubbles with a  mean diameter less than 90 microns.

It is noted that the L-4-J configuration had a somewhat higher gain  (bubbles-
per-horsepower) than the L-2-J unit although the bubble count at about the
same supply  pressure was lower.  This is because the L-4-J unit required
less pump power due to a lower flow resulting  from  the smaller vortex
chamber inlet diameter of the L-4 units compared  to the L-2  units, 0.1935
and 0.250 inches, respectively (see Table 2).

DISPERSON PATTERNS

For those vortex configurations producing  an adequate supply of bubbles in
the tank, the pattern of bubble dispersion was startlingly uniform. Shown
in the line drawing of Figure 36, this pattern comprised (for the vortex
device position shown) a relatively invariable  distribution in which the
thirty-inch wide region to the right contained what relatively small turbu-
lence was present  due to the vortex outflow.  The region to the left was a
relatively quiet zone having a uniformly high concentration of bubbles
with an average size slightly smaller than those on  the right.

The dimensions and location of the clear zone  remained relatively un-
changed for both vortex units and pressurization testing  (inlet shown  in
the lower, right-hand corner of Figure 36).

When the vortex device was moved to the right, no  significant change in
pattern  occurred.  When  it was  moved to the left, the clear zone narrowed
by almost exactly  as much as the vortex device was moved.  For leftward
movements of the vortex unit beyond about six inches, a clear zone began
to appear on  the right as well as on the left.  This indicates that the  zone

                                 56

-------
                                                     12
                                 VORTEX INFLOW     INCHES
    45
   INCHES
Cn
                                                  777
                                              30 INCHES
                                  100 INCHES
                                                                 FLOG MIXTURE
                                                              /INLET
y
                                                              fORTEX DEVICE
                                                                  L
      12 INCHES
               PRESSURI-
           ZATION SYSTEM
           INLETS
                                       FIGURE 36

                              TYPICAL BUBBLE DISPERSION PATTERN
                                                                           31826

-------
of total influence of the most effective vortex devices is a circle of
approximately 30 to 36 inches in diameter.  No significant change in
pattern occurred as the depth of the vortex unit within the tank was
changed as much as 1-1/2 feet.

"OUTSIDE" AIR ENTRAINMENT

The question of air entrainment on the outside of the conical sheet of
swirling fluid exiting from a vortex device was introduced previously.
Figures 16 through  20 describe the equipment used to evaluate the
concept.  As pointed out in Section V, two devices were actually
involved, one of them permitting the outside cone of the vortex to be
vented to ambient pressure and the other one inhibiting this venting.

Initially, the non-venting device was tested and was found to have
substantially only one axial position  in which it would entrain atmo-
spheric air.  All other positions resulted in the device blowing water
out of the aspiration tube. At the point where aspiration was possible,
so little air was entrained that a negligible quantity of bubbles were
produced in comparision with those generated  by "inside" aspiration.

When the vented device was substituted,  it was found to be operable as
an entrainer of atmospheric air over its whole  range of axial positions.
Moreover, a valve was required to throttle inlet air flow to the point
where only small bubbles  would be produced at all operating conditions.
Accordingly, the vortex unit with this device was operated over a range
of liquid pressures  and at various depths to determine whether any one
or more combinations of axial  position,  depth  and pressure would result
in a  significant quantity of small bubbles  being generated.

Unfortunately, no such combination was found which would in any way
compare with bubbles produced by "inside"  aspiration for the vented
unit.  Measurements of the air intake flow were of the order of 0.01 to
0.03 SCIS, or well  under the entrainment levels of the "inside" aspiration.
This comparison becomes  moot in light of  the superior performance demon-
strated by aspiration on the suction side of the pump over "inside" aspi-
ration.

PRESSURIZATION PROCESSES

During the course of the program, an opportunity presented  itself to
evaluate a form of the pressurization process which excludes a retention
tank in its design.  This  process was essentially identical to that which
was  used for final evaluation of the vortex device, except that the back

                                 58

-------
pressure regulator replaces the vortex unit. In essence, the process
makes use of air aspirated on the suction side of the pump; the air
passes through the pump where it is dissolved; the resulting pressurized
solution goes directly to a gate valve (back pressure regulator) and
thence to the bubble-making  tank.  If wastewater had been used instead
of tapwater, the solids could have clogged the gate valve, necessitating
the use of a more sophisticated back pressure regulator.  Subsequent
information supplied by EPA revealed that a similar system in South Africa
is employed in  a wastewater  renovation plant.  It was decided to determine
whether the process was effective, and how it compared in bubble-making
efficiency with both the tank pressurization process and the vortex bubble-
makers .

Although equipment for the tank process existed, the only work done
during initial testing to compare tank and tankless processes directly
involved two different bubble-making tanks and valve-piping arrangements.
As a result, photography was not attempted, and the two processes could
only be qualitatively judged as "comparable".  The modified test equip-
ment built for final test purposes had comparable valving and a common
inlet from both  processes to the bubble-making and flotation tank.
During the only test of the tank system with this modified equipment,
the pressurization tank ruptured before photographs could  be taken.
Therefore, no further work with the tank process was attempted and sub-
sequent evaluation consisted solely of a comparison between the tankless
process and the various vortex bubble-makers.

The tankless pressurizatio'n process was tested at various operating
water pressures and input air flow rates.  A gate valve was used to
simulate a conventional bubble-making nozzle.  As anticipated, best
performance was attained at maximum available water pressure with
maximum air flow short of that which caused pump binding.  Using the
same photographic site employed in the tertiary tests of the vortex
devices, 9900 bubbles per input horsepower were recorded at a water
pressure of 40.5 PSIG and an air flow of 0.60 SCIS.  The mean bubble
size was 67 microns in diameter.  Photomicrographs of bubbles formed
by this  process are shown in  Figures 37 through  40.  The test was run
continuously for 1-1/2 hours  without need for any readjusting or trimming
of the gate valve once the correct setting had been made.

The set-up for this tankless pressurization test included several branch
lines  off of the  pump line feeding the gate valve.  These had been in the
system for other test purposes.  It was recognized that these lines pro-
vided a volume  which might be functioning as a pressurization tank. If
so, the test would not be a true representation of a tankless pressurization
process.  Therefore, the  piping was rearranged to provide a close-coupled

                                 59

-------
                           FIGURE 37
PHOTOMICROGRAPH, TANKLESS PRESSURIZATION @ 40.5 PSIG & 0.60 SCIS
                          FIGURE 38
PHOTOMICROGRAPH, TANKLESS PRESSURIZATION @ 40.5 PSIG & 0.60 SCIS
                              60

-------
                          FIGURE 39
PHOTOMICROGRAPH, TANKLESS PRESSURIZATION @ 40.5 PSIG & 0.60 SCIS
                          FIGURE 40
PHOTOMICROGRAPH, TANKLESS PRESSURIZATION @ 40.5 PSIG & 0.60 SCIS
                              61

-------
direct line from the pump to the gate valve.  With this arrangement,
the system was operated for more than an hour, again without break-
down or the  need for readjusting or trimming once the correct valve
setting had been made.  A detailed analysis of the bubble formation of
this second  run was not made.  However, no apparent differences were
noted in either the general  bubble formation or photomicrographs of this
run. From these tests,  it is concluded that the tankless  pressurization
approach for dissolving  air in water can be  used in dissolved gas bubble-
making processes.
                                62

-------
                           SECTION VII

                       FLOTATION TESTING
Flotation screening tests were desired as part of the final evaluation of
vortex devices being developed under this program.  Such tests were
regarded as a suitable climax to the evaluation which made up the
major share of planned program work.  The testing was to be performed
under procedures supplied by the EPA,  using at least three mean bubble
sizes (50,  100 and 200 microns diameter). The main objective of these
tests was to be the determination of optimum bubble size for clarification.
Measurements of air flow and of water pressure and flow were also to be
taken to assist in the evaluation.

Using the concentrations of bentonite and aluminum sulfate described in
Section V,  a mixture was prepared and placed  in the initial,  cylindrical
flotation tank.  Initially, the mixture was stirred by circulation through
the pump. This was found to be unsuccessful, however, as any floe
which tended to  form was broken up by the impeller of the centrifugal
pump and subsequent attempts to float this floe were unsuccessful.
After this,  the mixture was stirred by hand, using  paddles, followed
then by another attempt at flotation. This second  attempt was at least
partially successful in that  a small amount of  relatively stable foam was
rapidly formed in the first two minutes.

Accordingly, the test system was modified as  described in Section V of
this report. When tested as a bubble-making  site, the new bubble-making
and flotation tank arrangement was highly successful, as outlined in
Section VI.  When tested as a flotation tank, however, no float was gene-
rated „   Neither the vortex device nor the pressurized process produced a
float when the various floe mixtures were introduced into the new flotation
tank.  The problem was due to the fact that the flotation tank was roughly
nine times  larger than the flocculation tank, which was  capable of only
batch operation.  Conversion of this latter tank to a continuous system
would have constituted the major portion of the solution to the problem.
Unfortunately, these extensive modifications to the flocculation and
mixing system were not possible within the time and funds remaining on
the program. Since the flotation testing actually represented a small
portion of the program, further work toward flotation testing was abandoned.
                                63

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                           SECTION VIII

                           DISCUSSION
GENERAL APPLICABILITY

The experimental results of this study verified that the vortex bubble
generator can produce small gas bubbles of less than 100 microns in
diameter.  It should be possible to use  these devices in any process
which requires bubbles of this size for its  operation.

The same vortex units can generate bubbles larger than 100 microns if
needed  for any of these processes.  By  increasing the air flow, larger
bubbles , up to 1/4-inch in diameter, can be formed.  The ability to
conveniently change bubble size over a wide range without mechanically
adjusting numerous units in an installation may be another advantage
over some of the conventional generators.

These devices should also be able to find application in aeration pro-
cesses  where gas  is bubbles through liquid for the purpose of dissolving
a portion or all of the gas into the liquid.  Air bubbles, for example,
can be used to oxygenate water in this manner.

OPERATING METHOD

The vortex bubble  generator has two possible methods of operation. In
both methods water under pressure enters the unit tangentially which
sets up the vortex motion within the unit.  In one of  the possible oper-
ating methods atmospheric  air is aspirated  into the center of the unit
through a separate inlet tube.  No air pump is needed because sufficient
vacuum exists to draw the air in.  In the second method of operation the
air enters the device dissolved in the pumped water.  No separate  air
tube is  needed.  Also, no air pump is needed if the air is added at the
inlet to the pump.

This second method proved to be more efficient than  the first in terms of
producing more bubbles per pumping horsepower.  In addition to this
advantage, it has  important installation advantages.  Most  obvious of
these is that only  one  supply pipe is needed.  The first operating method
would require an additional inlet pipe for each unit.  It is likely that an
air valve adjustment would be needed on each unit, particularly if the
quantity of air or if bubble  size were to be  changed.  Therefore, the
second  method is preferred for operating the vortex bubble generator.  It

                                65

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provides a dissolved gas bubble-making technique using devices which
need no adjusting when first installed or after long periods of operation
and are virtually free from clogging.

COST ESTIMATES

The vortex bubble generator is quite simple in its basic design and there-
fore can be produced at a relatively low cost. It can be made in two
pieces and bolted together with an O-ring or gasket providing a static
seal.  No moving parts are used.  In quantities of 20 to 100, the cost
per unit is estimated at $50 to $70. In higher production quantities the
cost could be reduced to under $20.

It is expected that a hardware cost comparison of conventinal dissolved
gas bubble generators and vortex generators will not reveal a significant
difference in initial cost.  The more important differences are expected to
be revealed in a maintenance and operating cbst comparison.

Tests conducted in this study show that a modified conventional pressuri-
zation system produces more bubbles per water pump power than the vortex
generator.  Further development  may improve  the vortex performance in this
regard but at this point it must be viewed  as a potential disadvantage when
comparing operating costs with those of conventional devices.  On the other
hand, the vortex unit has a potentially lower  maintenance cost advantage.
No situation can be foreseen which would require replacing, adjusting or
cleaning these devices.

The result of a cost trade-off probably depends to some extent on the
particular application.   In some  processes it  may be convenient  to conduct
routine maintenance at very little cost.  In other cases it may be very
important for production reasons  to run for a long period without  disruption.
For these reasons it would be appropriate to conduct a  pilot cost evaluation
program on an actual process.
                                66

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                           SECTION DC

                      ACKNOWLEDGMENTS
The program was performed during  1970 and 1971 by the Bowles Fluidics
Corporation of Silver Spring, Maryland.  Bowles personnel participating
in the program included L. W. Pearson, Project Manager;  R. J. Range
and R. F. Turek, Principal Engineers; L.  R. Moore and V.  F.  Neradka,
Senior Engineers; and J.  S.  Sims, Jr., Vice President.   Special thanks
are due to Mr. T. O'Farrell  of the EPA facility at the Blue  Plains Treat-
ment Plant of the District of Columbia.  The assistance of Mr. J. F.
Kreissl,  Project Officer, Environmental Protection Agency, Advanced
Waste Treatment Laboratory, Cincinnati, Ohio, is  gratefully acknow-
ledged.
                                67

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                             SECTION X

                            REFERENCES
 1.     "Formation of Gas Bubbles from Orifices," Jackson, Industrial
        Chemist, V.28, n. 331,332, August 1952, p. 1157-61.

 2.     "Experimental Study of Bubbles Moving in Liquids," Haberman and
        Morton, American Society of Civil Engineers — Proceedings, V.80,
        Separate n. 387, January  1954, 25 p.

 3.     "Formation of Gas Bubbles at Horizontal Orifices," Davidson,
        Amick, American Institute of Chemical Engineer Journal, V.2, n.3,
        September 1956, p.337-42.

 4.     "Formation of Bubbles  at Simple Orifices," Hughes, Handles, Evans,
        Maycock,  Chemical Engineering Progress, V.51, n.12, December
        1955, p.557-63.

 5.     "Air Bubbles in Water," Liebermann, Journal of Applied Physics,
        V.28, n.2, February 1957, p. 205-11.

 6.     "On the Instability of Small Gas Bubbles  Moving Uniformly in
        Various Liquids," Hartunian, Sears, Journal  of Fluid Mechanics,
        V.3,  Pt.l, October 1957, p. 27-47.

 7,8,9.  "Behavior of Small Permanent Gas Bubbles in Liquid," Zwich,
        Journal of Mathematics &  Physics. V.37, n.3,4, October 1958,
        p.246-68;  January 1959, p.339-53. p.354-70.

10.     "Formation of Gas Bubbles at Submerged  Orifices," Mayes, Hardy,
        Holland, American Institute of Chemical Engineer Journal, V.5, n.3,
        September 1959, p. 319-24.

11.     "Change of Size of Air Bubbles in Water Containing Small Dissolved
        Air Content," Manley,  British Journal of Applied Physics , V.  ll,n.l,
        January 1960, p.38-42.

12.     "Bubble Formation at Orifice in Viscous Liquid," Davidson, Schueler,
        Instn. Chemical Engineers, Transactions, V.38,  n.3,  1960,  p. 144-54,

13.     "Bubble Formation at Orifice in Inviscid Liquid," Davidson, Schueler,
        Instn. Chemical Engineers, Transactions, V.38,  n.6,  1960,  p.335-42,
                                 69

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14.     "Bubble Formation at Orifices in a Fluidized Bed," Harrison, Leung,
        Instn. Chemical Engineers, Transactions, V.39,  n.6,  1961,
        p.409-14.

15.     " Some Qualitative Observations of Bubble Behavior Resulting from
        Photographic and  Schlieren Studies," Rennie,  Chemical Engineering
        Science, V.18, n.9, September 1963,  p.641.

16.     "Similarity Rules  for Isothermal Bubble Growth,"  Langlois, Journal
        of Fluid Mechanics,  V.15, Pt. 1, January 1963, p.111-18.

17.     "Initial Motion of Gas Bubbles Formed in Inviscid Liquid," Walters ,
        Davidson, Journal of Fluid Mechanics. V.17,  Pt. 3, November 1963,
        p.321-36.

18.     "Formation of  Moderate Sized Bubbles," Mahoney, Wenzel, American
        Institute of Chemical Engineers Journal,  V.9,  n.5, September 1963,
        p.641-5.

19.     "Collapse and Rebound of Spherical Bubble in Water,"  Mickling,
        Plesset, Physics  of Fluids, V.7, n.l,  January 1964, p.7-14.

20.     "Asymptotic Growth of Bubbles in Liquid  with Uniform Initial
        Superheat," Bankoff, Applied Science Research, Section 2, V.12,
        n.3, 1963-64, p.267-81.

21.     "Formation of Air  Bubbles at Orifices Submerged Beneath Liquids,"
        Sullivan, Hardy,  Holland, American Institute of Chemical Engineers
        Journal, V.10, n.6, November 1964, p. 848-54.

22.     "Entrained Particle Trajectories in Swirling Flow," Hirschkron, Ehrich,
        ASME Paper No. 64-WA/FE-30.

23 .     " Gas Bubble Entrainment by Plunging Laminar  Liquid Jets , " Lin,
        Donnelly, American Institute of Chemical Engineers Journal, V.12,
        n.3, May 1966, P.563-71.

24.     " Behavior of Bubbles in Gas-Solid  Fluidized-Beds , " Toei,  Matsuno,
        Kojima, Nagai, Nakagawa, Yu, Kyoto  University  Faculty Engineering
        Memoirs, V.27, Pt. 4, October 1965,  p. 475-81.

25.     "Cavitation Bubble Collapse Observations in Venturis ," Ivany,
        Hammed, Mitchell, ASME Paper No. 6T-WA/FE-20.
                                  70

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26.     "Effect of Increase in Pressure on Collapsing Bubble Causing
        Cavitation," Mathew, Indian Journal of Technology, V.4, n.110,
        October 1966.  p.315-16.

27.     " Behavior of Air Bubbles in Dilute Aqueous Solutions ," Zieminski,
        Caron, Blackmore, Indus.  andEng. Chem. -Fundamentals, V.6,
        n.2, May 1967, p. 233-42.

28.     "Entrainment of Air into Liquid Spray," Briffa, Dombrowski, American
        Institute of Chemical Engineers Journal, V.24, n.4, July 1966,
        p.708-17.

29.     "Determination of Mass Transfer Coefficients and Interfacial Areas
        in Gas-Liquid  Contacting Systems," Dillon, Harris, Canadian
        Journal of Chemical Engineering,  V. 44, n. 6, December 1966,
        p.307-12.

30.     "On Growth of  Small Cavitation Bubbles by Convective Diffusion,"
        vanWijngaarden,  Int. J. Heat and Mass Transfer, V.10, n.2,
        February 1967, p. 127-39.

31.     "Formation of Bubbles," Krishnamurtmi, Kumar, Kuloor, Chemical
        Progress Engineering, V.49, n.l, January 1968,  P.91-7.

32.     "Experimental Study of Behavior of Single Bubbles," Zieminski,
        Raymond, Chemical Engineering Science, V. 23, n.l, January  1968,
        p. 17-28.

33.     "Coalescence  of Gas Bubbles in Aqueous Solutions of Inorganic
        Electrolytes,"  Marrucci, Nicodemo, Chemical Engineering Science,
        V.22, n.9, September 1967, p.1257-65.

34.     "Bubble Trajectories and Equilibrium Levels  in Vibrated Liquid
        Columns," Foster, Botts, Barbin, Vachon, ASME Paper No. 68-FE-l.

35.     "Behavior of Small Gas Bubbles in Accelerated Liquids," Gutti,
        American Society of Chemical Engineers —Proceedings, V.94,
        (J. Hydraulics Dev.) n.HY4, July 1968,  Paper 6047, p. 1073-82.

36.     "Analytical Description of Waiting Period Between Successive
        Vapor Bubbles  Formed During Nucleate  Boiling," Dzakowic, Frost,
        Heat Transfer and Fluid Mechanics Inst.— Proceedings, June  17,
        18,  1968, p. 98-115.
                                  71

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37.     "Babine Lake Bubbler System," Smith, Engineering Journal, V.51, n.3,
        March  1968, p.39-45.

38.     "Fluid Dynamics," Gill, Cole, Estrin, Nunge, Littman, Industrial
        and Engineering Chemistry, V.49,  n.12, December 1967,  p.69-105.

39.     "Bubble Drives Fluid Circulations , " DeNevers ,  American Institute
        of Chemical Engineers Journal, V.14, n.2, March 1968, p.222-6.

40.     "Investigation of Entrainment of Water by Stream of Successive Air
        Bubbles," Marks, Shreeve, ASME Paper No.  68-WA/FE-40.

41.     "Rise Velocity of  Bubbles in Tubes and Rectangular Channels as
        Predicted by Wave Theory," Maneri, Mendleson,  Chemical Engi -
        neering Progress Symposium, V.64, n.82,  1968, p.70-80.

42.     "Elements of Water Supply and Waste-Water Disposal, " Fair and
        Geyer, John Wiley and Sons, Inc. , New York, 1958.

43 .     "Marks' Mechanical Engineers' Handbook," Seventh Edition,  T.
        Baumeister, Editor, McGraw-Hill Book Company,  Inc., New York,
        1967.

44.     "Formulas for Stress and Strain, " Third Edition,  Roark, McGraw-Hill
        Book Company, Inc., New York, 1958.

45.     "Handbook of Physics, " Condon and Odishaw, Editors, McGraw-Hill
        Book Company, Inc. , New York 1958.

46.     "Water and Wastewater Engineering, "Volume 2,  'Water Purification
        and Wastewater Treatment, " Fair, Feyer, and Okun, John Wiley and
        Sons, Inc., New York,  1968.

47.     "Handbook of Fluid Dynamics," 1st Edition, V.L.  Streeter, Editor-in-
        Chief,  McGraw-Hill Book Company, Inc., New  York ,  1961.

48.     "Machinery's Handbook," 16th Edition, Oberg and Jones, The
        Industrial Press, New York, 1962.
                                   72

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                          SECTION XI

                   PUBLICATIONS AND PATENTS
No publications, patents or pending publications or patents have been
produced as a result of this project.
                                73

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Term






GPM




PSIG




SCIS




 V




 d




 f
Definition
SECTION XII




 GLOSSARY







      Units
Water flow rate




Pressure




Air flow rate




micron




Diameter




Frequency




Velocity
      gallons per minute




      pounds  per square inch gage




      standard cubic inches per second




      10~6 meters




      inch




      hertz




      feet per second
                               75

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   SELECTED WATER
   RESOURCES ABSTRACTS
   INPUT TRANSACTION FORM
                      1. Report No.
               2.
                         3. Accession No.
                                           w
  4.  Title
     FLUIDIC VORTEX BUBBLE GENERATOR
   7.  Author(s)
  9. Organization
    Bowles Fluidics  Corporation
    9347 Eraser Avenue
    Silver Spring, Maryland  20910

  12. Sponsoring Organization

  15. Supplementary Notes
                                           5. Report Data
                                           6,
                                           8. Performing Organizmtioa
                                             Report If 9.

                                           10. Project No.

                                             17030 FEB	
                                           11.  Contract/Grant No.

                                             14-12-863
                                           13.  Type of Report »Jtd
                                              Period Covered
  16. Abstract


    This  report contains the results of a detailed engineering investigation and
    evaluation of vortex devices  as  bubble-makers for use in  the removal of
    suspended solids  from wastewaters by flotation.  The specific objective  of
    the program was  the development  and test of  bubble-makers useful for generat-
    ing bubbles having mean diameters of about 100 microns with vortex devices
    having minimum liquid passageways of 1/4-inch or greater.  The overall concept
    of the program involved testing  the feasibility of improved methods for  reducing
    the cost of generating bubbles for the flotation of solids from wastewaters.
  17a. Descriptors
                *Waste Treatment,  *Flotation,  *Separation Techniques
  / 7b. Identifiers
                *Bubble Generation, *Vortex  Devices, Bubble Sizes, Bubble  Densities
  17c.CO WRR Field & Group  05 D
  18. Availability
19. Security Class.
   (Report)
                           20. Security Class.
                              (Page)
21. No. of
   Pages

22. Price
Send To:
                              WATER RESOURCES SCIENTIFIC INFORMATION CENTER
                              U.S. DEPARTMENT OF THE INTERIOR
                              WASHINGTON. D. C. 20240
  Abstractor James F. Kreissl
              /nst/*utionEPA-NERC,  Cincinnati,  Ohio 45268
WRSIC 102 (REV JUNE 1971)
                                                                                    GPO

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