;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
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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.
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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
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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
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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
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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
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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
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.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
-------
H
O
H
w
8
w
cu
40
35
30
25
20
. c
15
10
CT)
OO
OPERATION AT 36 PSIG
MICROSCOPE/CAMERA
MAGNIFICATION FACTOR
26.9
MEAN = 86 MICRONS
CO LO
LO ^ CO
^ CD r-H
oo LO
O CD 00 t*»
o oo c^ to
r^ oo o oj
^H r-l CSJ
-------
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
-------
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
-------
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
-------
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
-------
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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