1. NucE431W S2016
FINAL REPORT
Hybrid Cooling System
January 2016 through May 2016
By
Moza Alsalami
Mason Jacoby
Andrea Sinkpon
David Yang
The Pennsylvania State University
Department of Mechanical and Nuclear Engineering
University Park, PA 16802
April 29th
, 2016

2. 1
TABLE OF CONTENTS
Page
LIST OF FIGURES ......................................................................................................... 2
LIST OF TABLES........................................................................................................... 2
NOMENCLATURE ........................................................................................................ 3
ABSTRACT..................................................................................................................... 5
CHAPTER 1.INTRODUCTION..................................................................................... 5
1.1 DRY COOLING SYSTEM .......................................................................... 5
1.2 WET COOLING SYSTEM........................................................................... 6
1.3 HYBRID COOLING SYSTEM .................................................................... 6
CHAPTER 2.ANALYTICAL APPROACH ................................................................... 8
2.1 DETERMINATION OF SYSTEM PARAMETERS .................................. 8
2.2 SYSTEMS ORDER SELECTION .............................................................. 9
2.3 HYBRID OPERATION MODE SELECTION............................................. 12
CHAPTER 3.LAYOUTS................................................................................................. 15
CONCLUSION................................................................................................................ 20
RECOMMENDATIONS FOR FUTURE WORK .......................................................... 20
REFERENCES ................................................................................................................ 20

3. 2
LIST OF FIGURES
1.1 Series Configuration of the Hybrid Cooling System................................................. 7
2.1 Wet and Dry System Cooling Ranges ....................................................................... 12
2.2 Water Consumption Relative to Cooling Systems Operation Modes........................ 12
3.2 Basic Layouts for the Wet Section............................................................................. 15
3.2 Initial Layout Design ................................................................................................. 16
3.3 Circular Configuration with Round Towers .............................................................. 16
3.4 Zigzag Configuration with Round Towers ................................................................ 17
3.5 Back to Back 3D View .............................................................................................. 17
3.6 Round Combined Layout 3D View ........................................................................... 18
3.7 Round Layout top view with Dimensions ................................................................. 18
LIST OF TABLES
2.1 Design Data................................................................................................................ 11
2.2 Results........................................................................................................................ 11
2.3 Full Dry Cooling System Mode Data (wet section fans not running) ....................... 13
2.4 Full Wet Cooling System Mode Data (dry section fans not running) ....................... 13
2.5 Maximum Performance Mode (100% hybrid/dry 100% and wet section 100%) 14
2.6 Maximum Water Conservation Mode ....................................................................... 14
3.1 Comparison of Final Layouts..................................................................................... 19

4. 3
NOMENCLATURE:
The following terms are used in the report:
Name/Symbol Definition
Interference A portion of discharged vapor from one tower contaminating the
ambient intake of a nearby tower
Recirculation A portion of discharged vapor from one tower induced back into the
same tower air inlet
Heat duty The amount of energy the cooling system rejects to the 𝑊
environment from the working fluid.
% Heat duty The percent of total heat duty handled by the specified section
(dry or wet)
A Heat exchanger surface area per cell 𝑚!
C Heat capacity rate
!
!"# !
𝑐! Heat capacity
!
!"∗!
j Water loading (The water flow rate per land area (footprint))
!"
!"#∗!!
𝑚 Mass flow rate
!"
!"#
n Number of cells
N Number of transfer units
𝑄 Heat duty W
R Heat capacity rate ratio
𝑉 Air volumetric flow rate
!!
!"#
U Overall heat transfer coefficient
!
!∗!!
𝜌a Density of air
!"
!!

5. 4
Subscripts
a Air
cell Per cooling cell
dry Dry section
in Inlet
max Maximum value
min Minimum value
out Outlet
w Water
wet Wet section

6. 5
ABSTRACT:
The main objective of the project is to design a hybrid cooling system for a steam condenser in a
nuclear power plant. The hybrid system will be in a series configuration with dry section leading
a wet section. This report attempts to compute cooling system parameters, to validate the order
of the cooling systems, to select ideal operation mode with least water consumption and to
develop feasible layouts for the hybrid system. Using the typical water loading of 20 (t/m2
h) and
humidity ratio of 2.7, this report verifies that 36 cells are needed for the wet section to handle the
processing of 155000 (t/h) water flow rate and 443 (kg/s) is the required air flow rate in each
cell. The required number of dry cells was determined from the given heat duty handled by the
dry section of 30%. Using water flow rates the number of dry cells required was determined to
be 72. Also, using NTU method, this report demonstrates the advantage of the series hybrid
system with the dry section leading compared to the system with the wet section leading. It was
found that having the dry section coming first would allow more heat duty to be removed by the
dry section. Hence, water consumption in the wet system would be reduced. After selecting
number of cells and computing the performance of wet and dry cooling systems, hybrid
operation mode of 73% heat duty handled by wet section versus 27% heat duty handled by dry
section was selected as the maximum water conservation mode. Finally, the layouts presented in
this report are designed with considerations of their required construction area and airflow
restrictions
CHAPTER 1 INTRODUCTION
The focus of this chapter is to explore aspects of wet, dry and hybrid cooling systems. This
studying of the various cooling systems would enlarge the knowledge on each system’s
performance and would provide ideas on available layouts which can be used as basis in
developing the hybrid cooling system.
1.1 DRY COOLING SYSTEM:
Dry cooling system uses indirect cooling via a forced air draft to cool the working fluid which
passes through tubes. In the dry cooling system, heat is rejected from the working fluid to air that
is forced across metal tubes by a fan. This system does not bring the working fluid in contact
with the environment. In other words, no mass exchange occurs and no water is lost. Therefore,
the dry cooling system sees most use in regions of low water resources to reduce cooling system
water consumption. However, the dry system struggles in high ambient air temperatures as the
heat transfer is entirely dependent on the temperature difference between the working fluid and
the air. Also, the dry system performance is inversely proportional to the interference. In order to
minimize the incidence of interference between each dry cooling unit, these towers will be
positioned right next to each other, into one large air-cooled heat exchanger (Bechtel Power
Corporation, 2012).

7. 6
1.2 WET/EVAPORATIVE COOLING SYSTEM:
In the wet cooling system, heat is rejected to the environment through evaporation. This heat
transfer approach is achieved when the water flowing into the cooling tower gets into direct
contact with air. At the water-air interface, evaporation occurs following the principle of
diffusion from high vapor concentration region to the region with lower vapor concentration
(Kröger, 2004). Heat transfer enhancement in wet cooling towers is accomplished by the use of
fills to break the water into smaller droplets leading to an increase in both surface area of water
exposed to the air and its time of exposure (Bechtel Power Corporation, 2012).
According to Hensley (1983), the wet cooling tower performance is affected by factors such as
wet bulb temperature, interference and recirculation. The ambient air wet bulb temperature is
considered the main factor in governing the tower performance. Theoretically, the lowest
possible temperature of the cold water leaving the tower is the wet bulb temperature. Achieving
the wet bulb temperature requires very large and expensive towers (Bechtel Power Corporation,
2012). Also, the thermal performance of the cooling tower can be affected by interference and
recirculation (Hensley, 1983). To minimize the impact of interference and recirculation some
aspects of cooling towers such as draft type selection, cooling towers spacing and layout should
be considered. For this project, the draft was specified by the sponsor to be forced mechanical
draft, air is forced inside the cooling tower by fans. Groups of cooling towers should be at least
one group size apart to minimize the effect of interference (Bechtel Power Corporation, 2012).
Finally, layout selection is to be determined based on the required construction area, air
restriction and vulnerability to interference and recirculation.
There are two common wet system layouts that are available in wet cooling system industries:
rectangular and round. The rectangular layout can consist of one line or back-to-back cooling
towers. The round layout, on the other hand, can have the towers arranged in a circular or
octagonal configuration. After a careful studying of both layouts, it was concluded that round
layout is better than the linear layout for it is less vulnerable to recirculation, unaffected by wind
direction and able to handle more heat loads with less area impact compared to the linear layout
(Hensley, 1983). Thus, the round mechanical draft will be selected as the wet system layout for
this project if no other compatible layout is developed.
1.3 HYBRID COOLING SYSTEM:
Hybrid cooling systems consist of both wet and dry components. The technology chosen in this
paper is a combination of wet and dry cooling towers. The primary emphasis in this report is on a
closed-cycle cooling mechanism. In a closed loop system, cooling water is reused in a second
cycle instead of being discharged directly to the original water source. A closed loop system has
cooling towers that exposes water to the ambient air. While some of the water evaporates, the
rest of it goes back to the condenser in the power plant.
This closed-cycle system will be used as a normal power heat sink for the nuclear power plant
steam condenser. The system will consist of indirect mechanical draft air cooled heat exchangers
and mechanical draft evaporative cooling towers. The combination of these two systems will

8. 7
give rise to the hybrid cooling system.
Water evaporation plays a significant role in the design of cooling systems. In a closed cycle
cooling system, the cooling water flows into a cooling tower. These systems withdraw less water
than once-through cooling systems. In a once-through cooling system, water is taken from
nearby sources such as rivers, lakes or the ocean. The water is circulated through pipes to absorb
heat from the steam present in condensers. The warm water is discharged to a local water source.
Once-through cooling systems are simple, inexpensive and can be implemented in power plants
located near abundant water sources. However, once-through cooling systems cause disruptions
to the ecosystems because of the large amounts of water needed to run power plants.
However, closed cycle wet cooling systems consume large amounts of water through
evaporation. Therefore, a limitation exists on the amount of water that evaporates through the
hybrid cooling system. Hybrid cooling systems have the ability to reduce the water evaporated
by as much as 70 to 80 percent as opposed to full wet cooling systems depending on
environmental conditions. The specifications related to hybrid cooling systems are intended for
sites where water availability is scarce. In order to mitigate the large losses in steam cycle
capacity and plant efficiency associated with all- dry operation, the amount of water used during
the hottest periods of the year is limited. These systems can achieve substantial efficiency and
capacity advantages during the peak load periods of hot weather, as compared to an all-dry
system. Reducing water consumption and improving performance are crucial goals associated
with hybrid cooling systems.
Designing hybrid cooling systems requires making decisions about the configurations of the dry
and wet sections of the cooling towers. A large variety of arrangements exist for hybrid cooling
systems. Numerous tower options are available. They include the following:
● Single-structure combined tower or separate wet and dry towers
● Series or parallel airflow paths through the wet and dry systems
● Series or parallel connected cooling water circuits
A conceptual design of an indirect hybrid cooling system is represented in the figure 1.1. The
figure shows a series configuration for the hybrid system.
Figure 1.1: Series Configuration of the Hybrid Cooling System
The dry section has been selected to lead the wet section in series. Calculations to validate this
decision are discussed in section 2.2.

9. 8
CHAPTER 2 ANALYTICAL APPROACH
In this chapter, parameters pertaining to the wet section of the hybrid system are calculated,
systems order is selected and different operation modes of the hybrid system were examined.
Using water loading equation, water flow rates in the dry section and humidity ratio, the total
number of cells needed for the wet and dry cooling systems are obtained and required air flow
rate per wet cell is determined, respectively. The efficiency of the hybrid system using different
systems order is analyzed. The goal of these computations is to confirm that having the dry
section coming before the wet section is more efficient than having wet section first. Finally,
different operation modes are discussed. Variable definitions are in the nomenclature section on
page 4.
2.1 DETERMINATION OF SYSTEM PARAMETERS
The dry section of the hybrid-cooling tower consists of mechanical draft evaporative cooling
towers. Each dry cell consists of 12 heat exchanger bundles with the water flow rate of 598 kg/s.
the total recirculation flow rate of the water is 155,000t/h (43055.56 kg/s), the total number of
dry cells can be calculated as following:
𝑛 =
𝑚!
𝑚!"##.!
𝑛 =
43055.56(
𝑘𝑔
𝑠 )
598(
𝑘𝑔
𝑠 )
𝒏𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒅𝒓𝒚 𝒄𝒆𝒍𝒍𝒔 ≅ 𝟕𝟐 Cells
The wet section of the hybrid-cooling tower consists of mechanical draft evaporative cooling
towers. Given water flow rate of 155000 t/h, water loading of 20 t/m2
h and single cell area of
14.8 m x 14.8 m, the required overall dimensions and total number of wet cells can be calculated
as follows:
𝑤𝑎𝑡𝑒𝑟 𝑙𝑜𝑎𝑑𝑖𝑛𝑔 =
!"#$% !"#$!#%&'($)* !"#$% !"#$ !"#$
!""#$%& !"#$% !"#$ !"#! [!!]
=
!![
!
!
]
!"#$%& !" !"##$ ∗ !"#! !" !"#$%& !"## [!!]
𝑗 =
𝑚!
𝑛 ∗ 𝑎
𝑛 =
𝑚!
𝑗 ∗ 𝑎
=
155,000(
𝑡
ℎ)
20(
𝑡
𝑚!ℎ
) (14.8 ∗ 14.8)𝑚!

10. 9
𝒏𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒘𝒆𝒕 𝒄𝒆𝒍𝒍𝒔 = 𝟑𝟓. 𝟑𝟖 𝒄𝒆𝒍𝒍𝒔
The number of cells that will be needed for the wet section is 36 cells. This number was rounded
to 36 in order to facilitate layout design; it is more easily divisible by whole numbers than 35,
allowing for more layout options.
Given the humidity ratio of 2.7, the airflow rate per cell can be calculated with the following
equations:
𝑚!"##,! =
!! [
!
!
]
!"#$%& !" !"# !"##$
!.!""""# [
!"
!
]
! [
!
!
]
! [!" !" !"# !"#]
!.! [!" !" !"#$%]
1 ton (metric) / hour = 0.277778 kilogram/ second
𝑉!"##,! =
!!"##,!
!!
𝑚!"##,! =
!"" !!! [
!
!
]
!" !"# !"##$
!.!""""# [
!"
!
]
! [
!
!
]
! [!" !" !"# !"#]
!.! [!! !" !"#$%]
Mass flow rate of air per wet cell = 443 (
𝒌𝒈
𝒔
)
𝑉!"##,! =
!!" [
!"
!
]
!.!"#$ [
!"
!!]
Air volumetric flow rate per wet cell = 367.87 (
𝒎 𝟑
𝒔
)
2.2 SYSTEMS ORDER SELECTION:
The NTU/Effectiveness method was used to determine which section should lead in series; dry
or wet. Heat capacity must be determined for both cases in order to decide which is more
efficient for the system overall. The case where the dry section has a higher % heat duty should
be selected.
The effectiveness method uses different relations with effectiveness and the variables N (number
of transfer units) and R (heat capacity rate ratio).
𝐶!"#$% is shown below, 𝐶!"#is calculated similarly
𝐶!"#$% = 𝑐!,!"#$% ∗ 𝑚!"#$%

11. 10
The cross flow relation will be used as cross flow best represents the type of heat exchanger in
use.
Effectiveness can now be calculated from above. Effectiveness is related to heat transfer rate as
shown below:
Where
Combining the above equations and solving for Twater,out gives the equation below. This allows
calculation of heat duty given the temperature difference. Subscript ‘hot’ below represents the
working fluid (water).
Where
For dry section last in series, solve above for Twater,in

12. 11
Using given values below, heat duty can be calculated from determining 𝑇!"#$%,!"#,!"#for dry
section leading and 𝑇!"#$%,!",!"#for dry section trailing. These temperatures are the hybrid
system interface temperature.
𝐻𝑒𝑎𝑡 𝐷𝑢𝑡𝑦 = 𝑄 = 𝐶!"#$% ∗ (𝑇!"#$%,!",!"# − 𝑇!"#$%,!"#,!"#)
Where 𝑇!"#$%,!",!"#for dry section leading is 54.0°C and
𝑇!"#$%,!"#,!"# for dry section trailing is 37.8°C. Given values and results are shown below.
Table 2.1: Design Data
Results:
Table 2.2: Results
It can be seen that the dry section leading is significantly more efficient due to the higher
temperature difference and thus higher heat duty. The dry section benefits leading due to the
ambient temperature difference with the working fluid temperature.
Additionally, plots (Figure 2.3) were made to observe dry and wet section performance as a
function of the water interface temperature. The water interface temperature is the temperature of
the water at the point between the dry and wet sections in series. The dry section shows no water
temperature difference at the design point ambient temperature of 35°C. Temperature ranges
below 0°C are due to ambient temperature being higher than the working fluid temperature
which cause the working fluid to be heated. The wet section is capable of cooling water below

13. 12
the design point ambient temperature as is seen on the plot (~27°C). This plot shows that as the
interface water temperature increases, performance of both sections increases. This also shows
that the evaporation will increase as interface water temperature increases, so a balance is
required.
Figure 2.1: Wet and Dry Section Cooling Ranges
2.3 HYBRID OPERATION MODE SELECTION:
After analyzing the performance of wet and dry cooling systems, the next objective is to
determine the operation mode under which the hybrid system results in a maximum reduction in
water consumption compared to fully wet cooling system. To arrive at the maximum water
conservation mode, Figure 2.2 suggests that the dry system should operate at its maximum
capacity under the given ambient conditions (it is assumed that the percent heat duty removed by
the dry section is equal to the percent water conservation). In this section, the maximum capacity
of the dry section is examined and is used to set the maximum water conservation mode of the
hybrid system. Then, the aspects of water conservation and cold water temperature outputs
resulting from the maximum water conservation, maximum performance and full wet operation
modes are compared.
Figure 2.2: Water Consumption Relative to Cooling Systems Operation Modes
y = 0.2957x - 10.349
y = 0.7155x - 19.35
-5
0
5
10
15
20
20 25 30 35 40 45 50 55
DTwater
(°C)
Twater,interface
(°C)

14. 13
Using the equations obtained in section 2.2,
𝑇!"#$%,!"#,!"# = 1 − 𝐶! 𝐸 ×𝑇!"#$%,!",!"# + [(𝐶! 𝐸×𝑇!"#,!",!"#]
𝐻𝑒𝑎𝑡 𝐷𝑢𝑡𝑦 = 𝑄 = (𝑚 ×𝑐!×∆𝑇)!"#$%
the dry section is demonstrated to handle maximum heat duty of 780 MW as shown in Table 2.3.
Table 2.3: Fully Dry Cooling System Mode Data (wet section fans not running)
As the dry section can only cool down the water to 45.33o
C, wet system should be operated to
continue cooling down water to the required cold water temperature of 37.8 o
C .However, before
specifying the heat duty that should be removed by the wet system to get to the required cold
water temperature, it is important to examine its maximum capacity. Thus, using the equations
obtained from section 2.2,
∆𝑇!"# = [(0.7155×𝑇!"#$%,!",!"#) − 19.35]
𝐻𝑒𝑎𝑡 𝐷𝑢𝑡𝑦 = 𝑄 = (𝑚 ×𝑐!×∆𝑇)!"#$%
the wet section is demonstrated to have a capacity of handling 3470 MW of the condenser
required heat duty of 2900MW as shown in Table 2.4.
Table 2.4: Fully Wet Cooling System Mode Data (dry section fans not running)
As can be seen in Table 2.4, having the cooling system operating at 100% wet cooling system
mode would cool down the water temperature to 34.71o
C which is below the specified water
temperature of 37.8 o
C. Consequently, fully wet cooling system is a possible operation mode.
The next operation mode that was tested is the maximum performance mode, having the dry and
wet section operating at their maximum capacity. By the maximum performance mode, the
resulting heat duty was computed to be 3692MW as shown in Table 2.5.
Input Dry Section Data Wet Section Data Output
Hot Water
Temperature(⁰C)
T-
interface(⁰C)
Range Heat
Duty
(MW)
%Heat
Duty
T-
interface(⁰C)
Range Heat
Duty
(MW)
%Heat
Duty
Cold Water
Temperature(⁰C)
54 49.66 4.33 780.30 100 49.66 0 0 0 45.33
Dry Section Data Wet Section Data Output
T-interface =
Hot water
Temperature
((⁰C)
Range Heat
Duty
(MW)
%Heat
Duty
T-interface =
Hot water
Temperature
(⁰C)
Range Heat
Duty
(MW)
%Heat
Duty
Cold Water
Temperature(⁰C)
% Water
Conservation
Water
Conservation
(m^3/h)
54 0 0 0 54 19.29 3470.29 100 34.71 ~ 0 0

15. 14
Table 2.5: Maximum Performance Mode (100% hybrid/dry section at 100% and wet section at
100%)
Since the maximum performance mode outputs cold water temperature of 33.48 o
C, it is
considered to be a feasible mode of operation. Finally, the hybrid system was modeled to operate
at maximum water conservation mode by setting the dry section to operate at its maximum
capacity of 26.91% heat duty and wet section to handle 73.1% heat duty of the required
2900MWas shown in Table 2.6.
Table 2.6: Maximum Water Conservation Mode Data (100 % dry + minimum capacity wet to
meet cold water temp limit)
Dry Section Data Wet Section Data Output
T-
interface(⁰C)
Range Heat
Duty
(MW)
%Heat
Duty
T-
interface(⁰C)
Range Heat
Duty
(MW)
%Heat
Duty
Cold Water
Temperature(⁰C)
% Water
Conservation
Water
Conservation
(m^3/h)
49.66 4.34 780.30 26.91 49.66 11.78 2119.70 73.09 37.88 ~ 26.91 1076.28
Although the fully wet system and the maximum conservation mode of the hybrid system would
result in lower than 37.8 cold water temperature, which would had lower backdrop pressure and
thus higher turbine output power than the maximum water conservation mode of operation, water
conservation would be zero. On the other hand, the hybrid system maximum conservation mode
shows the advantage of the hybrid system in saving 26.91% of water consumed in fully wet
system and at the same time meeting the cold water temperature of 37.8 o
C.
Dry Section Data Wet Section Data Output
T-interface =
Hot water
Temperature
((⁰C)
Range Heat
Duty
(MW)
%Heat
Duty
T-interface =
Hot water
Temperature
(⁰C)
Range Heat
Duty
(MW)
%Heat
Duty
Cold Water
Temperature(⁰C)
% Water
Conservation
Water
Conservation
(m^3/h)
49.66 4.34 780.30 21.13 49.66 16.18 2912.11 78.88 33.48 ~ 0 0

16. 15
CHAPTER 3 LAYOUTS
To come up with hybrid system layouts, guidelines such as construction area utilization,
sufficient supply of fresh ambient air to cooling towers, interference and recirculation should be
considered. Using the above criteria along with the basic layouts, as shown in Figure 2.1, other
layouts were developed.
Various layouts were brainstormed in order to come up with appropriate configurations for the
36 wet towers. One of those initial layouts is demonstrated in Figure 3.2. Those layouts did not
work because they caused issues in terms of airflow in between towers. The air flow was not
equally distributed to every tower. From a managerial perspective, purchasing towers of different
sizes to accommodate changes in the air flow was not practical.
Thus far, two layouts are to be considered: round and zigzag as discussed below.
Figure 3.1: Basic Layouts for the Wet Section

17. 16
Figure 3.2: Initial Layout Design
The first layout to be discussed, as shown in Figure 3.3 is related to the round
arrangement of 36 wet cells. For land area purposes, the cells were not arranged in a back to back
configuration. In this first configuration, 9 wet cells are arranged around a circle of 71.7 m
(235ft) outer diameter. In order to evenly distribute the 36 cells, a total number of 4 circles are
needed. Each of the cells is separated by a distance of 14.7m (48.195ft). The land space occupied
by 9 towers is equal to 16152m² (173859ft²). The total area for 36 cells is equal to 46, 225m².
Figure 3.3: Circular Configuration with Round Towers
The second layout to be discussed is the zigzag configuration. The zigzag configuration
was separated into two units of equal length (119m). The two units contain 18 cells respectively.
The zigzag configuration is a unique design with a total land area of 7378m²(79416ft²). This
configuration is economical in terms of land usage. Further analysis would need to be completed
to determine the feasibility of this system.

18. 17
Figure 3.4: Zigzag Configuration with Round Towers
Combined layouts were also considered. The main focus was on the back to back and combined
round layouts discussed below. 3D models were developed of the back-to-back configuration
(Figure 3.5) and round combined configuration (3.6). This allows simple calculation of land area
usage and is a good visualization tool.
Figure 3.5: Back to Back 3D view

19. 18
Figure 3.6: Round Layout 3D view
Figure 3.7: Round Layout top view with dimensions
Figure 3.6 and 3.7 show the combined round layout. This layout consists of a circle of 9 wet cells
surrounded on the perimeter by 18 dry cells. Four blocks of these round systems are combined to

20. 19
make the total of 72 dry and 36 wet cells. The two layouts above (back to back and round
combined) were chosen to be compared and are represented in table 3.1 below.
Table 3.1: Comparison of final layouts
Area, airflow, recirculation and fan deck height were all considered in the comparison. The back
to back configuration is best at conserving area compared to the combined round layout. The
round layout is better in the other aspects versus the back to back layout. Dry section fan deck
height was considered as a way of comparing water pumping costs. The lower deck height of the
round system will save pumping head to lift water into the dry section versus the back to back
layout. There are other factors such as cost and total area allowed that would need to be
considered to move forward with the comparison.

21. 20
CONCLUSION:
After understanding the mechanism that each cooling system works upon, an emphasis was put
on computing wet and dry cooling system parameters, on selecting the order of the dry and wet
cooling systems in the series configuration, on selecting the ideal hybrid operation mode and on
developing hybrid system layouts. As was demonstrated in the report, it was found that having
the hot water flowing into the dry section first and then the wet section would result in the dry
section handling 27% of heat load as compared to handling 5% of heat load if it comes after the
wet section. In addition, it was found that to process the given water flow rate of 155,000 t/h, 36
cells and 443 kg/s of dry air per cell are needed for the wet section and 72 cells are needed for
the dry section. Also, it was found that having the dry section handling 27% heat duty and the
wet section handling 73% heat duty would result in 27% water conservation. Finally, three
layouts, round and zigzag, for the hybrid system were developed. The preferred layouts are either
back to back or combined round configuration. More analysis is required such as air flow
determination and cost analysis before a final decision could be made.
RECOMMENDATIONS FOR FUTURE WORK:
Future work on this project could be improved in a few areas. Cost analysis could be used to
determine the most economical operation mode as a function of water cost, fan operation costs
and power generated. More detailed land area information could facilitate more unique hybrid
system layouts. Additional performance calculations would allow for a more quantifiable
selection of hybrid system layouts although it may be beyond the scope of the course.
References:
1- Kröger, D. G. (2004). Air-cooled heat exchangers and cooling towers. Tulsa, Okl:
Penwell Corp.
2- Hensley, J. C. (Ed.). (1983). Cooling tower fundamentals. Marley Cooling Tower
Company.
3- Bechtel Power Corporation (2012). Alternative Cooling Technologies or Modifications
to the Existing Once-Through Cooling System for San Onofre Nuclear Generating
Station.