5223
001R77105
NEEDS FOR PLUME ANALYSIS
FOR THERF4AL AND TOXIC
POINT SOURCE DISCHARGES*
By
Mostafa A. Shirazi
Research Mechanical Engineer
U.S. Environmental Protection Agency
Pacific Northwest Environmental Research Laboratory
Corvallis, Oregon 97330
ABSTRACT
In order to satisfy a variety of regulatory needs related to monitoring,
enforcement and setting effluent standards for point source thermal
and toxic discharges, EPA has compiled a series of comprehensive nomograms
describing the physical behavior of thermal plumes that are particularly
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present paper discusses these needs and summarizes the two workbook
volumes containing these nomograms.
*For presentation at the U.S. - Japan Cooperative Science Program
Seminar on Engineering and Environmental Aspects of Waste Heat
Disposal, April 15-19, 1974, Tokyo, Japan.
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•/-TiCH AGENCY
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NEEDS FOR PLUME ANALYSIS FOR THERMAL AND TOXIC
POINT SOURCE DISCHARGES
INTRODUCTION1
In the United States the Environmental Protection Agency (EPA) is responsible
for conducting research, for establishing and enforcing standards, and for
monitoring pollution in the environment. An important responsibility
of EPA is to assist the states and local governments in their own
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EPA's functional and program responsibilities lie in the areas of
air, water, pesticides, solid waste and radiation. In the specific
program area of water, the legal tools necessary to attack the problems
of pollution control are provided in the 1972 Amendments to the
Federal Water Pollution Control Act.
The objective of the Act is to restore and maintain the chemical,
physical and biological integrity of the Nation's waters. The 1972
Amendments changed the thrust of enforcement from water quality
standards, regulating the amount of pollutants in a given body of
water, to effluent limitations, regulating the amount of pollutant
being discharged from a particular point source. Ambient water quality
requirements can still dictate the amount of pollutants permitted
for each discharge.
EPA is directed to establish guidelines for effluent limitations,
identifying the best practicable control technology available for
various discharge categories. These requirements must be met by
appropriate dischargers by 1977. In addition, EPA must identify the best
Regulatory and policy related matters are obtained directly from
Reference 1.
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available technology for preventing and reducing pollution. These
requirements must be met by all dischargers by 1983. The goal (not
necessarily the requirement) of the act is to eliminate all discharges
by 1985.
It is recognized that application of the best practicable or best
available waste treatment technology may not always provide an effluent
of receiving water quality. In order to accommodate the discharge of
water which, at the end of the pipe, will viol ate receiving water
quality sldriudrdb, an area of mixing is specified. The size of this
"mixing zone" is limited to an area which will not cause unacceptable
biological stress. Thus, a "mixing zone" is an area where receiving
water quality standards do not apply and its size is limited by
biological considerations. "Mixing zones" apply to all pollutants
including waste heat.
With respect to thermal discharaes, the 1972 Amendments state that
if the thermal discharger can demonstrate that an EPA limitation is more
stringent than that necessary to protect the propagation of fish, shell
fish and wildlife, then EPA may permit less stringent control, on a case
by case basfs.
Therefore, in all levels of federal and regional EPA activities related
to establishing and enforcing laws, issuing permits or monitoring
point source related discharges, the need for comprehensive understanding
of jet and plume behavior exists in order to determine if "mixing zone"
limitations are being met. Furthermore, the need for such understanding
exists within the state and local government regulatory agencies as
well as by participating private citizens.
The majority of those having the need for understanding the physical
behavior of plumes lack sufficient mathematical and thermodynamic
backgrounds required for direct use of plume models. This necessitates
that the material be presented to them in a non-technical language
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and yet in a concise manner so that the applicability as well as the
limitations of the solutions are clearly understood by such users.
Fortunately this task is facilitated in part by the fact that the
needs do not require exact plume calculations. The ultimate goal
is the protection of water quality based on available biological
criteria with an adequate margin of safety.- Results based on current
methods of analysis for predicting the physical behavior of the
plume can well satisfy the accuracy achievable in the biological prediction
of possible effects in the environment.
PLUME EXAMPLES
Only a few problems of general interest can be readily analyzed
and presented in a comprehensive manner so that a non-specialist
user can feel at ease with. The problem of a deeply submerged
bouyant jet is one such example that is relatively well understood
and ufuviueb dn excellent opportunity for demonstrating certain general
features of a real plume, including the interaction of jet bouyancy
and inertia! forces with the ambient water.
Reference 2, prepared by EPA, presents a comprehensive treatment of
the subject. It is titled "Workbook of Thermal Plume Prediction Volume
I, Submerged Discharges." The workbook contains numerous nomograms
showing plume characteristics such as trajectory, temperature and
width. Data and analyses from numerous sources are presented in
a unified format that is sufficiently simple for a non-specialist user.
Basic assumptions are carefully stated, and the user is reasonably
well guided against misapplication of the information.
Table 1 shows the type of problems addressed in the workbook for
various flow conditions and diffusers. All computed trajectories and
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plume widths(W) are presented in dimension!ess forms using the
jet diameter (D) as a reference. The jet and ambient temperatures are
used to calculate the local center!ine excess temperature ratios.
Corresponding to each entry in Table 1 there are given a group of
nomograms describing the jet behavior for several Froude numbers (F),
angles of discharge (0), stratification numbers ($t), and velocity
ratios. Figure numbers for the nomograms in each group are cross
referenced with the jet characteristics and tabulated for easy use.
For example, Table 2 lists the figure numbers for 35 nomograms for
a discharge into stagnant water at various angles of discharge with
the horizontal and for several specific diffuser configurations.
The nomograms are presented in pairs. For example, Figures 1 and 2
corresponding to Figures A-l and A-2 are presented as one pair in
the workbook. The first Figure contains temperature-trajectory information
and the second, width-trajectory information. The pages containing
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The user is given a physical explanation of the solutions given by
the nomograms. For example, with regards to plume dilution as a
function of Froude number, Figure 1 shows that as Froude number decreases
the plume dilution increases rapidly as indicated by the converging
temperature lines near the vertical axis. This is explained by the
fact that for two identical jet velocities and diameters, the jet
with a low Froude number has a greater total momentum due to bouyancy,
thus causing greater mixing.
Presenting the nomograms for the discharge into a stratified body
of water in a general form was particularly difficult because of
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dependence on the inital discharge level as well as other parameters.
The workbook assumes discharges to take place at various depths z below
the thermocline as shown in Figure 3. An example of the nomograms is
given in Figure 4. It is explained in the workbook that for a very
large stratification number approaching infinity the plume rises
indefinitely. In an environment with a finite stratification the plume
initially entrains cool water and carries it into warmer layers of
water above it. The plume temperature continues to drop while the
temperature of the surrounding water continues to increase with
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bouyancy but continues rising because of its excess momentum even when
its centerline temperature at a point along its trajectory equals
the local ambient temperature. This excess momentum carries the plume
from this point to its terminal height.
Other nomograms for conditions of discharge into an ambient current
and for shallow discharges are also provided in the workbook. Practical
example problems are worked out, not only to show the mechanics of
using the nomograms, but also to direct the attention of the user
to possible pitfalls of misusing the nomograms for problems they
are not intended for.
The second volume of the workbook is devoted to surface discharges (3).
In the preface, the reader is introduced to the subject in this
manner. "The nomograms provide qualitative results describing the
surface plume trajectory, width, temperature, depth, surface area
and time of travel along the plume centerline. The nomograms are
not intended to be used as exclusive design tools for the surface
discharge problem nor for use in a precise prediction of specific
plume conditions. "
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The nomograms are referenced the same way as in the first volume
by providing tables, with figure numbers corresponding to specific
discharge conditions. Tables 3 and 4 show this information as well
as the range of values for which working nomograms are presented.
In addition to what is referred to as "working nomograms" a set of
supplementary nomograms are also provided in the workbook. The working
nomograms are distinguished from the supplementary nomograms in that
the user is not required to specify the program coefficients, such
as the turbulent exchange coefficient, drag coefficient, shear and
entrainment coefficients. The workbook has made this decision for
the user by fitting the program to the mean of a reasonably wide
range of data. The supplementary nomograms are intended for special
applications where the stated coefficients are known to deviate substantially
from those recommended in the workbook.
Figure 5 is an example of a typical temperature, trajectory, width
and depth nomogram showing the effects of ambient current on all
plume characteristics. The plots are presented for constant jet
densimetric Froude number F, channel total width to depth aspect ratio
A, dimensionless heat exchange coefficient K, and angle of discharge TH.
The dashed lines along the trajectories are made proportional to
the local plume depth.
As in the first volume, considerable effort is devoted to familiarize
the user with the physics of the problem so that the user gains an
intuitive understanding of the nomograms. For example, temperature,
trajectory, width and depth plots similar to Figure 5 for variable
ambient current are presented to show the effects of variable jet Froude
number (see Figure 6), jet aspect ratio (see Figure 7) and initial
discharge angle (see Figure 8) on the plume characteristics.
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These figures show that plume penetration across an ambient current is
enhanced by (1) small ambient current, (2) small densimetric Froude
number F, (3) large jet aspect ratio A, and (4) a large angle of
discharge. Furthermore, generally hot and wide plumes are found
under the same four discharge conditions. Neither the ambient
current nor the discharge angle seem to influence the plume depth
greatly. A small discharge Froude number causes a thin plume due to its
tendency to stratification.
The workbook contains nomograms for the surface plume areas influenced
by given isotherms. An example of this type is given in Figure 9.
Additional plume information directly useful for ecological studies
is the time of travel along the plume centerline. An example of this
type of information is given in Figure 10.
CLOSURE
The foregoing examples of plume analysis demonstrate the way EPA has
attempted to present a very complex technical problem to benefit those
within government agencies in their decision making processes as
well as to invite a wider participation of non-government groups to
understand and to mount an integrated attack on pollution. It is an
attempt to narrow the gap between "what the scientist knows and what
the citizen understands." A gap which must be narrowed to
enable the "citizen...to make intelligent, effective decisions about
the patterns and problems of growth...1
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REFERENCES
1. Ruckelshaus, William D. "The Challenge of the Environment: A
Primer on EPA's Statutory Authority" U.S. Environmental Protection
Agency, Dec. 1972.
2. Shirazi, M. A. and Davis, L. R. "Workbook of Thermal Plume
Prediction, Volume I Submerged Discharges." Environmental Protection
Technology Series EPA-R2-005a, August 1972.
3. Shirazi, M. A. and Davis, L. R. "Workbook of Thermal Plume Prediction
Volume II, Surface Discharges" Environmental Protection Agency,
March 1974.
4. Russell E. Train, From an address to the American Association for the
Advancement of Science in San Francisco, Feb. 25, 1974.
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TABLE 1**
Summary of Subjects for Submerged Heated
Jet Discharge Presented
in Reference (2)
Diffuser
Configuration
Single
Round
Port
A Row of
Multiple
Round Ports
Condition of Ambient Water
Non-Stratified
No Current
RNN
MNN
Moving
RCN
MCN*
Stratified
No Current
RNS
MNS
Moving
RCS
MCS*
*Nomograms not presented for these cases.
**A three-letter code is used for convenient reference. First letter
designates type of diffuser; second letter, the type of current; third
letter, the degree of stratification.
10
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TABLE 2
Figure Numbers Corresponding to Plume Behavior
From Submerged Diffusers Discharging into
Stagnant, Non-Stratified Water
from Reference (2)
Diffuser
RNN
C -i vt n 1 f\
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Jet
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D. to
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CM
II
Q
1
CD
CO
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Discharge Angle
0°
A-l ,2
A-8,9
A-l 5, 16
A-22,23
A-29,30
30°
A- 3 4
A-10,11
A-17,18
A-24,25
A-31,32
60°
A- 5, 6
A-12,13
A-19,20
A-26,27
A-33,34
90°
A-7
A-14
A-21
A-28
A-35
11
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TABLE 3
.Figure Numbers for (TTWD) Working
Nomograms for 0- = 90° and K = lO"5
from Reference (3)
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1
5
10
15
2
Al
A5
A9
A13
4
A2
A6
A10
A14
6
A3
A7
All
A15
10
A4
A8
A12
A16
TABLE 4
Summary cf Figure Numbers for (TTWD)
Working Nomograms
from Reference (3)
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io-5
io-4
io-6
90°
Al -Al 6
A49-A64 *
A97-A112
60°
A17-A32
A65-A80
A113-A128
120°
A33-A48
A81 -A96
A128-A144
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20 40 60 80 100 120 140 160 180 200
LONGITUDINAL DISTANCE X/H0
FIG( 5 ) TEMPERATURE,TRAJECTORY,WIDTH, AND DEPTH
(TTWD)-PLOTS FOR SURFACE JET DISCHARGE
SHOWING EFFECTS OF AMBIENT CURRENT
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300
280
260
240
220
200
180
160
140
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60
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20 40 60 80 100 120 140 160 180 200
LONGITUDINAL DISTANCE X/H0
FIG( 6 ) TEMPERATURE,TRAJECTORY,WIDTH,AND DEPTH
(TTWD)-PLOTS FOR SURFACE JET DISCHARGE
SHOWING EFFECTS OF OENSIMETRIC FROUDE
NUMBER
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20 40 60 80 100 120 140 160 180 200
LONGITUDINAL DISTANCE X/H0
FIG( 7 ) TEMPERATURE,TRAJECTORY, WIDTH, AND DEPTH
(TTWD)-PLOTS FOR SURFACE JET DISCHARGE
SHOWING EFFECTS OF JET ASPECT RATIO
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300
280
260
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LONGITUDINAL DISTANCE X/H0
FIG( 8 ) TEMPERATURE,TRAJECTORY,WIDTH, AND DEPTH
(TTWD)-PLOTS FOR SURFACE JET DISCHARGE
SHOWING EFFECTS OF DISCHARGE ANGLE
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