HomeMy WebLinkAboutChena Feasibility Study Chena River Thermal Discharge Study 1983 ENA FEASIBILITY STUDY
ER THERMAL DISCHARGE STUDY
Prepared for
Morrison—Knudsen Company, Inc.
By
MARK MILES & DR. ROBERT F. CARLSON
INSTITUTE OF WATER RESOURCES
UNIVERSITY OF AK, FAIRBANKS
July 19, 1983
3443 «. WAL aia
Institute of Water Resources/ IWR 83-2
Engineering Experiment Station
UNIVERSITY OF ALASKA, FAIRBANKS
Fairbanks, Alaska 99701
July 19, 1983 RECE IVED : y
JUL 2 2 i993
Morrison-Knudsen Company, Inc. POWER DESIGN Power Group R :
Attn: Roger J. Landon Ec
One Morrison-Knudson Plaza H -EIVED P.0. Box 7808 rr Boise, ID 83729 ¥ 2 1983
ALAS WE Dear Mr. Landon: XA Power AUTHORITY
Please find the enclosed final draft of the project completion report of
the Chena River thermal discharge study for your review. If you have any questions or comments, please call.
Tom D. Roberts
Director
(907) 474-7775
TDR: 71983
Enclosure
| File Code: 163 102.
| J. Date: ¥.3-.260+ /
CHENA RIVER THERMAL DISCHARGE STUDY
by
Mark Miles
and
Dr. Robert F. Carlson
Institute of Water Resources
University of Alaska
Fairbanks, AK 99701
Prepared for
Morrison-Knudsen Company, Inc.
One Morrison Knudsen Plaza
Box 7808
Boise, Idaho 83729
Contract M-K W.0. No. 4036-03
Supported by
Alaska Power Authority
Completion Report 83-2
INTRODUCTION
Ice fog generally occurs in the subarctic when water vapor is
released to the atmosphere at air temperatures of less than
approximately -20°F (Walker and Brunner, 1982). Mechanisms for the
release of water vapor include automobile emissions, household heating,
and thermal discharge from power generating stations. The thermal
discharge, when released into an ice covered river or cooling pond,
causes an area of open water that is dependent on climatic factors and
the heat input for its size. This open water is a major source of water
vapor transfer to the atmosphere for the formation of ice fog.
This report describes a study of the relationship between thermal
discharges and ice fog formation on the Chena River in Fairbanks,
Alaska, during the 1982-83 winter season. The objective of the research
was to evaluate the response of the production of ice fog to a change in
the amount of thermal discharge from the MUS power plant. To meet this
objective, the response to heat input of the area of open water
downstream of the thermal discharged would be characterized. This
relationship, in turn, would be used in comparing discharge rate and
temperature, to the amount of vapor rejection from the open water
surface. This evaluation was performed using an energy balance
approach, where all heat inputs are balanced with the heat outputs. The
key to this approach is the calculation of a heat transfer coefficient,
which characterizes the rate at which heat is lost from the open water
surface given a temperature differential between the river water and the
air. In order to do this, the amount of heat added by thermal
discharge, the Chena River flow rate, the amount of open water area
downstream of the discharge, and local climate information were
characterized.
Most of the field work was carried out by University of Alaska,
Institute of Water Resources technicians Sara Morely and Cathy Egan.
Data analysis and literature review was performed by a graduate student,
Mark Miles, as a research assistant. The final analysis was supervised
Dr. Robert F. Carlson.
It was found during the course of this study that the area of water
caused by the thermal discharge was directly proportional to the amount
of heat added and inversely proportional to the air-water temperature
differential. The vapor transfer rate was found to be directly
proportional to air-water temperature differential and wind speed while
the total volume of vapor transfer was found to be directly proportional
to the wind speed, the amount of heat added by the thermal discharge,
and independent of the difference in the temperature of the water and
air.
When applied specifically to MUS thermal discharge, these
relationships show that the amount of water vapor transfer to the
atmosphere will be proportional to the amount of heat added, assuming
equal wind speeds. Thus, if the thermal discharge is increased by 50
percent, the amount of vapor transfer will also increase by 50 percent.
Although there is little firm knowledge of the relationship between
evaporative vapor transfer and the formation of ice fog, it is known
that there is a direct relationship between available water vapor and
ice fog production for a given air temperature. The proportion of water
vapor that forms ice fog also increases with lower air temperatures,
however, for a given set of climatic conditions, the amount of ice fog
resulting from the MUS thermal discharge will be directly proportional
to the amount of heat added by that thermal discharge. Thus, given the
proper air temperature, an increase in thermal discharge by a certain
percentage will increase the amount of ice fog by approximately the same
percentage.
LITERATURE REVIEW
A literature review to gather information from previous studies was
initiated in late November of 1982. Various data bases were computer
searched to aid the literature review. The results of the search
yielded few pertinent documents concerning thermal discharge and ice fog
problems. Most of the literature focused on the meteorological aspects
of ice fog instead of the heat transfer of thermal pollution from a
subarctic stream. Those found to be most informative included:
a3
McFadden, 1974; Michel, 1971; Paily, 1974; and Dingman and Assur, 1969.
All discussed the winter regime thermal response of heated water in more
or less detail, and were used to evaluate methodology and to assess the
accuracy of the results of this study.
McFadden's study (1974) in particular was the most detailed and
helpful. This study took place at the nearby Eielson AFB power plant
cooling ponds. It performed an in depth heat transfer analysis of
thermal discharge and the resulting ice fog, and analyzed several
methods for ice fog suppression on cooling ponds. The paper presents
values for the heat transfer coefficient and also performs an in depth
analysis of evaporative heat loss.
Michel (1971) discusses the heat balance on open water in winter,
focusing on the convective, evaporative and radiative heat losses, as
well as a brief discussion on mass transfer.
Paily (1974), in his Ph.D. thesis for the University of Iowa,
discusses the temperature distribution downstream from a thermal
discharge, and the length of the reach that will be kept ice free by the
heat input. This study also developed a complex heat loss model
applicable to both field and laboratory situations and presents
experimentally developed heat loss coefficients.
Dingman and Assur (1969) present a method for calculating the heat
loss from a river below a source of thermal pollution and the length of
ice free reach that can be maintained by such a source. The paper
describes a simplified approach where the heat loss is calculated by
applying a heat transfer coefficient to the temperature differential
between the water and the atmosphere.
DATA COLLECTION
In order to update the existing data and to properly characterize
the thermal discharge and the winter thermal regime of the Chena River
adjacent to the MUS power plant, a monitoring program was initiated in
late November of 1982, and continued through mid-March of 1983. Five
major parameters were monitored: (1) thermal discharge flow rate, (2)
thermal discharge temperature, (3) open water area, (4) Chena River flow
rate, and (5) local climate information.
Thermal Discharge Flow Rate
Thermal discharge flow rate was monitored continuously using a
Leopold and Stevens Type F water level recorder with a gage scale of
1:5. The gage was installed in the outfall structure of the MUS power
plant. The installation included a small stilling well immediately
upstream of the 10 foot wide weir in the outfall structure, topped by a
platform which housed the water level recorder. Water levels recorded
on the strip charts were very constant, showing only one or two minor
vaiations in a week's time. These water levels were evaluated for
average weekly values using an HP-9845 computer and digitizer by
measuring the area under the recorded trace and then dividing by the
time length. A standard uncontracted weir formula (Albertson et al.,
1960) was used to compute discharge from the average weekly stage.
Q = 3.33Lh2/2 (1)
where
Q discharge in Ft?/sec
length of weir crest in feet
head of water on weir in feet.
Average weekly thermal discharge flow rates are presented in Table 1.
Table 1. Average weekly thermal discharge flow rate in #t?/sec.
Week Average Depth Average Disgharge, No. Date to water (ft) Head tet)! (ft~/sec)
1 12/1-12/7 -- -- (17.5)
2 12/8-12/14 -- -- (17.5)
3 12/15-12/21 -- -- (17.5)
4 12/22-12/28 13.92 0.62 16.3
5 12/29-1/4 13.76 0.78 22.9
6 1/5-1/11 13.91 0.63 16.7
7 1/12-1/18 13.90 0.64 17.0
8 1/19-1/25 13.90 0.64 17.0
9 1/26-2/1 13.81 0.73 20.8
10 2/2-2/8 13.93 0.61 15.9
11 2/9-2/15 13185) 0.69 19.1
12 2/16-2/22 13.90 0.64 1720
13 2/23-3/1 13.89 0.65 17.5
14 3/2-3/8 13.96 0.58 14.7
15 3/9-3/15 13.96 0.58 14.7
Average: 17/35)
1 Depth to weir = 14.54 ft. from measuring point.
Values in parentheses indicate where the average value was used in
place of missing values for general calculations.
Thermal Discharge Temperature
Thermal discharge temperature was monitored continuously using a
Russtrack thermistor probe recorder mounted on the stilling well
platform in the MUS power plant outfall structure. Strip charts of the
recorded temperature were evaluated for average weekly values using an
HP-9845 computer and digitizer in a similar manner as the average stage
was evaluated. Average weekly discharge temperatures are presented in
Table 2.
It was found that the Russtrack recorder was affected by the high
humidity environment of the outfall structure. Portions of each week's
record were found to be unreliable as they showed unaccountably extreme
and rapid fluctuations in temperature. Only those portions of the
record that showed fairly constant and verifiable temperature were used
for the average weekly value computations. These values were verified
by hand measurements. An average thermal discharge of 149 million
Btu/hr was calculated using these values and the discharge flow rate
values. The average, which is somewhat less than the maximum, compares
favorably with the heat rejection capacity of the MUS power plant rated
at 204 million Btu/hr (Landon, 1983).
Table 2. Average weekly thermal discharge temperature
Thermal Discharge Temperature
Week No. Date °¢ of!
1 12/1-12/7 -- (69.9)
2 12/8-12/14 -- (69.9)
3 12/15-12/21 -- (69.9)
4 12/22-12/28 -- (69.9)
5 12/29-1/4 -- (69.9)
6 1/5-1/11 20.9 69.6
7 1/12-1/18 20.6 69.1
8 1/19-1/25 20.6 69.1
9 1/26-2/1 21.8 71.2
10 2/2-2/8 (Alay 70.2
11 2/9-2/15 lee 70.2
12 2/16-2/22 <8 64.0
13 2/23-3/1 22e7 7239
14 3/2-3/8 22-0 7126
15 3/9-3/15 21.9 71.4
Average: 69.9
1 Values in parentheses indicate where the average value was used in
place of missing values for general calculations.
aps
FAIRBANKS M.U.S. POWER PLANT AND
OUTFALL
CHENA RIVER
Figure 1. Approximate survey station locations. Anproximate scale: 1" = 889 ft.
Open Water Area
The area of open water on the Chena River downstream of the MUS
outfall structure was measured weekly using an abney level and leveling
rod. A survey grid of 17 stations over a river reach of approximately
one mile was constructed based on previous years' observations of the
extent of open water (Figure 1). Surveyed widths were transferred to 1"
= 200' mylar overlays and the areas planimetered using the HP-9845 and
digitizer. Due to warmer than anticipated air temperatures, open water
areas progressed further downstream than survey stations allowed for
Measurement. Visual observations of the downstream extent of open water
were made and included on the mylars and planimetered. Table 3 presents
these measured and estimated total areas of open water and the change in
the area for the time periods between observations.
Table 3. Open water areas.
Open water area Open water area AA, change in ice
Week No. Date measured (#t2x10°) estimated (#t2x10°) area (#t2/dayx10°)
1 12/7 §.5212 5.7212 --
2 12/16 6.2644 11.1360 0.7734
3 12/21 5.9092 10.4400 -0.0991
4 12/28 5.5024 9.2700 -0.1671
5 1/4 3.0576 3.0576* -0.8875
6 1/13 2.3003 2.3003* -0.1082
7 1/18 5.5086 8.0800 0.8257
8 1/25 4.9108 5.1508 -0.4185
9 2/2 5.3144 9.6050 0.6363
10 2/9 5.2754 9.2600 -0.0493
11 2/15 4.2566 6.2640 -0.4280
12 2/22 4.8896 6.5120 0.0354
13 3/1 4.7440 8.1900 0.2397
14 3/11 5.5804 9.5400 0.1929
15 3/18 5.4124 8.1900 -0.1929
* Limit of open water adjacent to Station 1. Estimate not required.
Chena River Flow Rate
Daily Chena River flow data were obtained from the U.S. Geological
Survey office in Fairbanks, Alaska. These data are estimates from
monthly flow measurements and are subject to revision at a later date.
They are, however, accurate enough for the purposes of this study
(Vaill, 1983). Weekly averages were calculated from this information
and are presented in Table 4.
Table 4. Chena River flow rates.
Week No. Date Flow (#t3/sec)
1 12/1-12/7 367
2 12/8-12/14 360
3 12/15-12/21 358
4 12/22-12/28 350
5 12/29-1/4 347
6 1/5-1/11 310
7 1/12-1/18 250
8 1/19-1/25 223
9 1/26-2/1 211
10 2/2-2/8 210
11 2/9-2/15 210
12 2/16-2/22 200
13 2/23-3/1 200
14 3/2-3/8 200
15 3/9-3/15 200
Local Climate Information
Daily values of local climate data were obtained from the Fairbanks
office of the National Weather Service. Information of particular
interest for the evaluation of heat transfer from a water surface are
=10=
air temperature and wind speed. These data were evaluated for weekly
averages and are presented in Table 5.
Table 5. Local climate data.
Air temperature Wind Speed
Week No. Date (°F) (ft/sec)
1 12/1-12/7 -11.0 4.82
2 12/8-12/14 8.0 8.44
3 12/15-12/21 Sal, 6.60
4 12/22-12/28 -2.0 5.20
5 12/29-1/4 11.4 7.98
6 1/5-1/11 -36.6 4.04
7 1/12-1/18 -16.7 Saal
8 1/19-1/25 -3.6 6.20
9 1/26-2/1 10.4 7.06
10 2/2-2/8 12.9 6.81
LL 2/9-2/15 -4.0 byt5
12 2/16-2/22 -8.0 5.20
13 2/23-3/1 11.6 10.16
14 3/2-3/8 Se) 3.94
15 3/9-3/15 6.9 11.13
STUDY RESULTS
Heat transfer from the open water area of the Chena River below the
MUS power plant was evaluated using an energy balance approach. This
approach balances the amount of heat input by the thermal discharge, the
Chena River inflow, and the heat released by ice growth, with the heat
loss from the open water surface, and the outflow of the Chena River.
The use of this method allows for the calculation of the heat transfer
coefficient, which then may be used in predicting the effects of future
thermal discharges from the power plant, including vapor transfer rates
and volumes. Vapor transfer rates and volumes can then be used in
-ll-
assessing the relative magnitude of increase or decrease of ice fog
production. A relationship derived for thermal discharge versus vapor
transfer was established and is presented in this section.
Heat Balance of Open Water Area
The heat balance of the open water caused by the thermal discharge
from the MUS power plant can be summarized by the equation
Qag * 9% +94 = Qo * Qcur* Asur (2)
where
Q,; = heat advected in by the Chena River flow (Btu/day)
% = heat input from thermal discharge (Btu/day)
Q; = heat released or absorbed for ice growth or melting (Btu/day)
0rO = heat advected out by the Chena River at the downstream limit
of open water (Btu/day)
Qour = heat loss from open water surface to atmosphere (Btu/ft-day)
Rea = area of open water caused by thermal discharge (#2)
The heat advected into the system can be defined as
Qaq = 0% O* Vag* Ty (3)
where
p = density of water (62.4 1b/ft?)
c = heat capacity of water (1 Btu/1b-°F)
ris volume rate of flow of the Chena River directly above outfall
structure (Ft3/sec)
Te = temperature of water flow (=32°F)
The heat added by the thermal discharge can be defined in a similar
manner, where
= * * * Q, = o* Co* VO* Th (4)
-12-
where
V = volume rate of flow of thermal discharge (#t9/day)
T = temperature of thermal discharge (°F)
The heat released or absorbed due to ice growth or melting is
defined as
Ry = pq” 4" be (5)
where
oi = density of ice (57.2 1b/ft°)
V; = volume rate of ice growth (#t3/day)
Le = heat of fusion (144 Btu/1b)
The heat advected out of the system, where the ice cover resumes
downstream is defined as
Qao = O* c,* Veo" Tw (6)
where
vO = volume rate of flow of the Chena River out of the system
(Ft3/day)
i = temperature of water (=32°F)
The heat loss from the open water surface to the air generally takes
the form (Carlson, 1982)
Onn = Kl + K2* (Ty - T,) (7)
where
Kl = heat input from solar radiation (Btu/ft2-day)
K2 = heat transfer coefficient (Btu/ft?-day-°F)
T, = air temperature (°F)
The heat input from solar radiation can generally be neglected for
an area at the latitude of Fairbanks during the winter months as the
values are small compared to the amount of heat loss. The heat transfer
=13-
coefficient (K2), however, is a significant factor in determining the
amount of heat lost to the air from the open water surface. This
coefficient is a function of radiative, conductive and evaporative heat
loss, which are in turn functions of air temperature, wind speed, and
humidity. However, McFadden's (1974) findings indicate that the heat
transfer coefficient remains fairly constant throughout the range of
winter climatic conditions. The heat transfer coefficient may then be
evaluated empirically given the air temperature and heat inputs by
combining equations 2 through 7.
p* c.* (Ve Tat Vb Tp aN oe i) + Q; = k2* To - 1) (8)
and since va = ved - Yo
Ko = 0 Sy Vp (Ty = Ty) +5 (9)
Acuy My - Ta)
assuming an ice growth rate of 0.4 ft/week, we get
xo = 02.4 V (T. - 32) + 470.7* AA (10)
Raye (32 - i)
Calculation of Heat Transfer Coefficient
The heat transfer coefficient for the heat loss from the open water
surface to the air below the MUS power plant can be calculated using the
data collected during the 1982-83 winter season. These values are
presented in Table 6. A 90% confidence interval of the calculated heat
transfer coefficient using these data is 157 + 23.1 Btu/ft?-day°F.
The outlier value for week 5 was not included in this calculation.
This value is anomalous and does not accurately reflect the conditions
during that week. The temperature range was 61°F, from 35°F to -26°F as
the week progressed. This had the effect of giving a high average
weekly temperature and a low open water area, thus inflating the
calculated heat transfer coefficient.
-14-
Table 6. Calculated heat transfer coefficient (K2).
Week No. Date K2 (Btu/ft@day°F)
1 12/1-12/7 --
2 12/8-12/14 138552
3 12/15-12/21 118.4
4 12/22-12/28 105.4
5 12/29-1/4 (736.3)
6 1/5-1/11 214.2
7 1/12-1/18 87.4
8 1/19-1/25 183.9
9 1/26-2/1 21333
10 2/2-2/8 185.0
Hell 2/9-2/15 L335)
12 2/16-2/22 112.7
13 2/23-3/1 231.6
14 3/2-3/8 125.4
15 3/9-3/15 15155
Average Ko = 157 + 23.1 (90% confidence)
Vapor Transfer from Open Water Surface
In order to assess the amount of vapor transferred from the open
water surface, and thus the amount of ice fog caused by the thermal
discharge, an analysis of the evaporative heat loss over a water surface
must be performed. It has been estimated that heat loss due to
evaporation from an open water surface during the winter months accounts
for a major proportion of the total heat loss; on the order of 25
percent (McFadden, 1974).
Michel (1971) indicates that the evaporative heat loss over a water
surface can be related to the mass of evaporated water by
ve = m* L (11)
-15-
where
heat loss due to evaporation (Btu/ft2-day) ve 7
L = latent heat of vaporization (1,073 Btu/1b)
m = rate of vapor transfer (1b/ft2-day)
The evaporative heat loss can also be described by the equation as
indicated by Carlson (1982)
pee He Ty -T ) (12) a
where He is the evaporative heat transfer coefficient, which is
defined
as
H, =H (13)
where g is the Bowen's number, which is defined as
B= Coa” oa* RFT, (14)
L
where
Coa = heat capacity of air (0.24 Btu/1b-°F) o, = density of air (0.076 1b/ft®)
R = universal gas constant (85.75 ft/°F)
TG = temperature of the water surface (=32°F)
L = latent heat of vaporization (1,073 Btu/1b)
He is the convective heat transfer coefficient in
Btu/ft2-day-°F, which is given as
c a “pa *86,400 [sec/day] (15)
-16-
where
K = Von Karman's universal constant, usually 0.4
U = wind speed (ft/sec)
zy = surface roughness coefficient
Z = height at which wind speed is measured.
A is the slope of saturation vapor pressure versus air temperature
curve at a given air temperature. For the purposes of this study, it is
considered constant at 0.3 1b/ft2-°F as it does not vary significantly
at the air temperatures considered.
Combining equations 11 through 15 and simplifying, yields the
relationships
= 0.0247* U* AT - uy, (16)
Vem BAe (17)
p
where
m = rate of vapor transfer (1b/#t2-day)
V = total volume of vapor transfer (#t9/day)
Computed mass transfer rates and volumes are presented in Table 7.
These values illustrate the relative magnitude of vapor transfer given
air temperature, wind speed, and open water area. As discussed in the
following sections, the total volume of vapor transfer will increase
proportionally with an increase in thermal discharge.
a1]
Table 7. Vapor transfer from open water.
Week No. Date m_(1b/ft2day) Volume (ft?/dayx10*) 1 12/1-12/7 5.12 4.69 2 12/8-12/14 5.00 8.92 3 12/15-12/21 4.71 7.88 4 12/22-12/28 4.37 6.49 5 12/29-1/4 4.06 1.99 6 1/5-1/11 6.85 2.53 7 1/12-1/18 6.15 7.96 8 1/19-1/25 5.45 4.50 9 1/26-2/1 3.77 5.80 10 2/2-2/8 3.21 4.76 ll 2/9-2/15 4.58 4.60 12 2/16-2/22 5.14 5.36 13 2/23-3/1 5.12 6.72 14 3/2-3/8 2.56 3.91 15 3/9-3/15 6.90 7.20
4.87 1b/ftday
or 0.903 in/day
Vapor Transfer Versus Thermal Discharge Relationship
In order to assess the effect of increasing or decreasing the
amount of thermal discharge from the MUS power plant on the production
of ice fog, a relationship characterizing the amount of vapor transfer
caused by the thermal discharge must be examined. This general
relationship can be derived by combining equations 9 and 17. By using
the calculated average heat transfer coefficient, and by neglecting the
heat input or output due to ice formation or melting, an estimation of
the open water area can be applied to the mass transfer rate equation to
yield an estimate of the total volume of water vapor (V) released to the
air, given air temperature (T,)> wind speed (U), a thermal discharge
temperature (T,). and flow rate (V,). The heat of fusion absorbed
S19
or released due to ice formation or melting can be neglected at this
point since the amount of heat released (or absorbed) is approximately
three orders of magnitude less than that of the thermal discharge. The
resulting equation can be written as
_ 0.0247* U* V - 1) .
Vv p Tp (Ft3/day) (18)
K2
This relationship can also be written as
V= 0.0095* u* Qp (19)
K2
where
u = wind speed (ft/sec)
Qp = thermal discharge (Btu/hr)
K2 = heat transfer coefficient (Btu/ft?-day-°F)
Equations 16 through 19 show that, while the rate of vapor transfer
is directly proportional to the air-water temperature difference and the
wind speed, the total volume of vapor transfer is independent of air
temperature and is a function of thermal discharge and wind speed, only.
It should be noted that equations 18 and 19 will underestimate the
amount of vapor transfer at very low wind speeds where convective air
circulation adds to the transfer process. However, these equations are
sufficient to illustrate the relative magnitude of vapor transfer with
respect to thermal discharges.
SUMMARY AND CONCLUSIONS
The open water on the Chena River caused by the thermal discharge
from the MUS power plant is the source of a large proportion of ice fog
occurring in the Fairbanks area. Benson (1965) indicates that greater
than half of the ice fog occurring in the area is caused by the open
water surfaces of the Fort Wainwright and MUS power plants. To evaluate
=195
the effect of thermal discharges on ice fog production, an estimation of
the amount of open water caused by the discharge, and the amount of heat
transfer occurring from that open water must be performed in order to
estimate the total volume of vapor rejected due to the heat input of the
discharge.
The heat transfer from the open water area was investigated in this
study using an energy balance approach to evaluate the heat transfer
coefficient. The heat transfer coefficient, calculated empirically to
be on the order of 157 Btu/ft?-day-°F, agrees fairly well with values
found in current literature. Calculations performed by Paily (1974)
resulted in an average heat transfer coefficient from a water surface
equal to 142 Btu/ft?-day-°F, while Dingman and Assur (1969)
calculations indicate a heat transfer coefficient of 119
Btu/ft?-day-°F. McFadden's (1974) findings were somewhat lower,
giving an average heat transfer coefficient of about 70
Btu/ft?-day-°F. However, the conditions of that study were somewhat
different in that all observations were made in power plant cooling
ponds, and not on a river.
The findings of this study indicate that it is possible to estimate
the area of open water caused by thermal discharge on the Chena River in
a general fashion using the calculated heat transfer coefficient,
thermal input, and the average winter air temperature in equation 10 to
evaluate the effects of various thermal discharges.
Concurrently, the thermal discharge can be related to the amount of
possible vapor rejection, which, if the air temperatures are less than
approximately -20°F (Walker and Brunner, 1982), may cause ice fog. This
study found that an average of 0.9 inches/day of water vapor was
rejected from the open water surface of the Chena River. This value is
similar to McFadden's (1974) findings of vapor rejection of 0.2
inches/day from the cooling ponds. Thus, an estimation of future
thermal discharge effects on ice fog production may be performed.
Equation 16 can be used to estimate the vapor rejection rate, given the
average winter wind velocity and the surface temperature - air
temperature difference. The total volume of vapor rejection given a
thermal discharge amount and the heat transfer coefficient, as well as
the wind speed, can be estimated using equation 18 or 19. For example,
=20=
the data collected during the 1982-83 winter season indicated the
average thermal discharge was about 149 x 10° Btu/hr. The maximum
projected additional waste heat supplied by Chena 7 is on the order of
152 million Btu/hr. With maximum extraction for district heating, this
amount could approach 40 million Btu/hr. However, it is likely that the
amount of heat to be rejected will fall somewhere between the two
extremes (Landon, 1983). If once through cooling is utilized rather
than a dry condensor system, this additional heat effectively increases
the thermal discharge from 25 to 100 percent. Equation 19 indicates
that the amount of vapor transfer, and thus, ice fog, will increase by
the same factor.
LITERATURE CITED
Albertson, M.L., J.R. Barton, and D.B. Simons. 1960. Fluid mechanics
for engineers. Prentice-Hall Civil Engineering and Engineering
Mechanics Series.
Benson, C.S. 1965. Ice fog: low temperature air pollution.
University of Alaska Publication, Geophysical Institute UAG 173.
Carlson, R.F. 1982. Class notes. Arctic Hydrology and Hydraulic
Engineering, CE 683, University of Alaska, Fairbanks, AK.
Dingman, S.L. and A. Assur. 1969. The effects of thermal pollution on
river ice conditions. U.S. Army Cold Regions Research and
Engineering Laboratories, Hanover, N.H.
Landon, R.J. 1983. Personal communication. Morrison-Knudsen Company,
Inc., Power Group. Boise, ID.
Michel, B. 1971. Winter regime of rivers and lakes. Cold Regions
Science and Engineering, Monograph III-Bla. U.S. Army Corps of
Engineers Cold Regions Research and Engineering Laboratory,
Hanover, N.H.
=O1—
Paily, P. 1974. Winter regime thermal response of heated streams.
Ph.D. Thesis, Dept. of Mechanics and Hydraulics, University of
Iowa, Iowa City, IA.
Vaill, J.E. 1983. Personal communication. U.S. Geological Survey,
Water Resources Division, Fairbanks, AK.
Walker, K.E., and W. Brunner. 1982. Suppression of ice fog from the
Fort Wainwright, Alaska, cooling pond. Special Report 82-22, U.S.
Army Cold Regions Research and Engineering Laboratory, Hanover,
N.H.
-22-