THE NATIONAL UNIVERSITY OF

SINGAPORE

Department of Chemical & Biomolecular Engineering

CN4121

Design of Cooling Tower

Name: Zou Changlong U083731A

Data: 19/03/2012

2

Contents

Basic design ....................................................................................5

Computation scheme ......................................................................6

Calculation and results ...................................................................7

Step 1) Driving force and NTU (KaV/L) Calculation .....................7

Step 2) Plot Design NTU Curve .....................................................9

Step 3) Fill Selection ................................................................... 10

Step 4) Optimal L/G value selection............................................. 12

Step 5) Other Calculation............................................................ 17

Appendix ........................................................................................ 21

Reference ........................................................................................ 29

3

Nomenclature

Hot water temperature

Cold water temperature

Wet bulb temperature

Dry bulb temperature

Enthalpy of saturated air, kJ/kg

ℎ Enthalpy of moist air, kJ/kg

Enthalpy of exit air, kJ/kg

Enthalpy of inlet air, kJ/kg

Flowrate,

L Mass flowrate of liquid, kg/h

G Mass flowrate of gas, kg/h

Relative humidity

4

Introduction of cooling towers

The synthesis of ethyl benzene is a very exothermal process. The temperature of raw product is

so high that need to be cooled down to a moderate temperature before it goes to distillation

column or storage. Generally, the excess heat from the synthesis process is transferred to cooling

water. If the temperature is high enough, the heat can also be used to generate steam which can

be used in distillation column or next process. However, most unwanted excess heat has to be

released to the environment without creating ecological hazard and havoc or adding unnecessary

expense by using cooling water as intermedia. Hence, cooling tower is introduced to cool down

the cooling water and recycle it, which not only solve the possible ecological problem caused by

releasing hot water directly to environment but also recycle most water to decrease the

investment of cooling process and do help to the crisis of world’s water supply.

Cooling tower is a thermodynamic artifact combined with a recalculating water system that

serving as a transport medium for heat exchanging between heat source and heat sink. [11]

Cooling towers mainly have two divisions: Nature draft and Mechanical draft.

For Nature draft, the driving force of air flows is attributed by the buoyancy which is cause by

the difference between the densities of warm moist air and dry air. It usually uses very large

concrete chimney which is applied for water flow rates above . [12]

For Mechanical draft, fans are used to force or induce air flow through cooling towers. The

position of fans determines that whether it is forced draft type or induced draft type. The hot

water falls downward over fill surfaces which maximum the contact time between water and air

which maximize heat transfer process.

Cooling towers are also classified into counter flow and cross flow type. However, in theories

and practical, counter flow is more efficiency than cross flow [15]

, because it provides more

contact surface and time.

Cooling tower selection

In Singapore, chemical plan size is limited by the geometry of Singapore which indicates that

small size cooling tower is preferred. The average high temperature and humidity also limit the

5

type of cooling tower. Hence, Nature draft cooling tower is not applicable, because its cooling

efficiency would be very small in high air temperature and humidity, and its size would be very

large in order to fulfill the cooling requirement. For the forced draft type, the back flow of moist

air at top and the big energy request of fans at bottom would be troubles. It can be concluded that

an induced draft counter flow cooling tower is a better choice. The basic structure of this kind of

cooling tower is shown in Figure 1.

Cooling tower design and calculation

Basic design

The designing stream data is according to the Hysys simulating result. The dry air temperature

and relative humidity is according to the literature.[6]

For the determination of cooling water

outlet temperature, the outlet temperature should not excess based on industrial safety

requirement.[12]

Hence, the designing cooling water inlet temperature is set to be after

taking account of 10% safety margin for varying of temperature. With known dry bulb

temperature and relatively humidity, wet bulb temperature of air can be read from Psychrometric

Figure 1, basic structure of cooling tower. a) Fan, b) Water

distribution, c) Fill packing, d) Drift eliminators, e) Cold

water basin, f) Air inlet louver.[1][2][15]

6

figure or calculated by Psychrometric calculator. When dry bulb temperature is , and

relatively humidity is 80%, wet bulb temperature should be . In practical, approach is

seldom closer than . [6][12]

The cooling water outlet temperature is initially set to be

then changed to be based on the calculation of NTUs.

Computation scheme

Step 1: Use the Merkel equation to calculate the

driving force and NTU numbers with an initial guess

L/G ratio.

Step 2: Vary the L/G ratio and redo step one. The

NTU numbers for different L/G ration can be

obtained to generate a demand curve of cooling

tower. (Design NTU curve)

Step 3: Set L/G ratio to be 0.75 and 1.5 and calculate

the volume transfer coefficient (Ka/L) for different

fill types. Then calculate the packed height for

different fill types and select the one which gives the

lowest packed height.

Step 4: Calculate the air loading, pressure drop, fan

power, dimension of tower and etc. for the selected

fill with different L/G ratio. Compare the results and

find out the optimal L/G ratio.

Step 5: Based on the optimal L/G ratio, calculate the

rest information and data for cooling tower.

7

Calculation and results

Capacity (Q): (including 10% safety margin)

Dry bulb temperature of air ( ):

Wet bulb temperature of air ( ):

Relative humidity ( ): 80%

Cooling water inlet ( ):

Cooling water outlet ( ): (initial design )

Altitude (Z): 0 m.

Approach

Heat load

Step 1) Driving force and NTU (KaV/L) Calculation

According to the Merkel theory, the driving force of heat transfer is proportional to the

differences between the enthalpy of saturated air at the water temperature and the enthalpy of

unsaturated air at the point contacting with water.

Forward finite difference method is applied to solve the integration equation. Divide the

temperature range into n small segments so that the integration part can be replaced by[2]

:

Then, the cooling characteristic KaV/L which is a degree of difficulty to cooling can be

approximately calculated.

8

For most cooling tower, evaporation lost is negligible compared to the total amount of cooling

water.[1][2]

Based on this assumption, heat balance for cooling tower can be simplified into:

Therefore

Hence, an equation representing the air operating line of the cooling tower can be obtained:

By using equation (5), any point lying on the air operating line can be calculated.

Combined with saturation curve in Psychrometric, the driving force can be schematized on

Figure 2.

The area enclosed by saturation curve and air operating line is proportional to the total amount of

driving force which equal to the sum of NTU numbers and KaV/L.

Figure 2, Driving force diagram [6][4]

9

Sample calculation:

According to the industrial design, L/G usually is from 0.75-1.5 for counter flow induced draft

cooling tower. KaV/L is usually from 0.5-2.5.[1][6][4]

For initial design:

hw for all temperature points and are calculated by using Psychrometric calculator.(Appendix

1) Then, the rest ha is calculated by equation (5) for all temperature points. NTU numbers for

each temperature can be calculated using equation (2), which can be summed up to calculate

KaV/L. Results are listed in Appendix 2.

The results show that:

This result is out off the normal range of KaV/L values. Besides, when L/G varies slightly

towards to 1.8, sum of NTU numbers shoot up to around 200 and encounter negative value of

NTU during calculation (Appendix 3). This indicates that the cooling water outlet temperature is

too close to the wet bulb temperature which lead to very small driving force for heat transfer.

When L/G increases, the air operating line is getting too close to the saturation curve, even

crossing it at last. It results in big or negative NTU numbers which is not desirable. Considering

such reasons, the cooling water outlet temperature need to be adjusted littler high to decrease

NTU numbers. After some trials, the cooling water outlet temperature is set to be .

Step 2) Plot Design NTU Curve

Repeat step 1 calculation procedure for L/G varying from 0.4 to 2. Use Matlab to do the loop

calculation for different L/G and plot the sum of NTUs against their L/G values respectively.

Results are presented in Appendix 4 and Figure 3.

10

This curve is also known as design NTU curve. For every L/G value, it has an unique NTU and

KaV/L number, which also indicates that the tower characteristic term KaV/L is only influenced

by L/G.[1][2][4][6][9]

Step 3) Fill Selection

Fill is an important structure in cooling tower, because it provides sufficient contacting surface

for air and water to transfer hear. This step aims to choose a better fill from different types of

fills by comparing their packed height for certain L/G. Generally, 16 different arrangements of

triangular splash bars, flat asbestos sheet, corrugated asbestos sheets, rectangular splash bars,

asbestos louvers and typical cellular constructions are commonly used in industry.[2][3]

The

packed height of the tower is calculated directly using the data of Lowe and Christie.[3]

The

volume transfer coefficient Ka/L is represented by the equation:

where and are coefficients that define the transfer characteristics of this type of packing. For

different types of packing, their coefficients are summarized in Table 1.

Figure 3, relation between L/G and KaV/L (NTUs)

11

The details of structure and shape of these fills are presented in Appendix 5. Considering the

industry L/G range 0.75 to 1.5, volume transfer coefficient Ka/L of each type of packing is

calculated for smallest L/G (0.75) and largest L/G (1.5) respectively. According to the results

obtain in Step 2, KaV/L values for each NTU is already known. Then, the packed height can be

calculated by dividing KaV/L by volume transfer coefficient Ka/L just gotten.

For example, when L/G equals 0.75, for type PN-1:

All other result is shown in Appendix 6.

Table 1, coefficients of different packing type [3]

12

Compared with the capital cost caused by tower’s height, the difference between capital costs of

different packing masteries can be negated, which indicates that the height of packing is the

crucial factor. Hence, the best packing type should give the smallest packed heights compared to

others’ at the same L/G value.[7]

After analyzing the result data, it can be found that the packed height V of type PN-11 is the

smallest one for both L/Gs. It can be concluded that PN-11 packing is the best choice for this

cooling tower design. Packed heights of PN-11for other L/G values are listed in Table 2.

L/G NTU(KaV/L) Ka/L V (m)

0.75 1.509326 1.39287468 1.083605

0.8 1.547576 1.33479044 1.159415

0.85 1.588224 1.28243685 1.238442

0.9 1.631519 1.23495867 1.321112

0.95 1.677749 1.19166696 1.407901

1 1.727243 1.152 1.499343

1.05 1.780386 1.11549478 1.596051

1.1 1.837629 1.08176595 1.698731

1.15 1.899501 1.05048996 1.808205

1.2 1.966632 1.02139295 1.925441

1.25 2.039775 0.99424146 2.051589

1.3 2.11984 0.9688351 2.18803

1.35 2.20794 0.94500083 2.336442

1.4 2.30545 0.92258837 2.498893

1.45 2.41409 0.90146651 2.677958

1.5 2.536048 0.88152016 2.876903

Step 4) Optimal L/G value selection

The type of packing is determined to be PN-11. The next main object is to find the optimal L/G

value for the cooling tower.

In design targeting, the objective is to minimize the total cost which consists of capital and

operational cost.[7][10][13]

The capital cost mainly includes cost of tower, fills, fan and pump. The

Table 2, packed heights of PN-11

13

operational cost is mainly contributed by makeup water, operating of fan and pump which is

related directly to their powers.

Calculation of dimensions

The tower floor area is determined by the equation:

where water loading can be approximately determined from Figure 4.

Figure 4, Sizing char for counter flow induced draft cooling tower[6]

The water concentration is .

Tower floor area is:

Then the overall height of tower can be calculated empirically as[3]

:

ℎ ℎ ℎ

For n number of packing cells,

Referring to the industry, the flow rate per cell should less than [10][11], because too

large flow rate will decrease the performance of packing. Considering a big total flow rate of

, it is better to use 6 cells instead of single cell in order to guarantee a good cooling

performance and avoid too big height.[14][15]

Hence, over height for different L/G values from

0.75 to 1.5 can be calculated.

For example, when L/G equals 0.75,

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ℎ ℎ

Hence the dimensions of cooling tower is , total volume of

tower is:

Other results are listed in Appendix 7.

Operational cost of cooling tower

Calculation of fans’ power

The power of induced fan is determined by the discharge rate Q which represents the amount of

air need to be induced. It can be determined by knowing the total water flow rate through the

tower[3]

.

where TWFR is the total flow rate ( ), is the density of saturated air leaving the tower

( . Then, the horsepower required to drive the fans can be empirically calculated using a

rule of thumb that each 226.5 of air discharged by the fan requires 1 hp, approximately

0.75 kW. The total flow rate is constant. Hence, the power is related to L/G values and saturated

air density at outlet. Assuming the humidity of outlet air is 99%, for different L/G values, the

enthalpy of outlet air is varying, which indicates that temperature is varying according to L/G

values. That leads to different densities for different L/G values. For L/G changes from 0.75 to

1.5 at 0.05 step size, enthalpy of outlet air can be calculated from equation (5) respectively. The

temperature and density can be calculated by trial and error method using Psychrometric

calculator. For example, when L/G equals 0.75

Varying the dry bulb temperature with Psychrometric calculator until the enthalpy is fitted. Then:

15

Hence:

Other results with rest L/G values are listed in Appendix 7&8.

Calculation of Pump’s power

For a counter flow type cooling tower with spray nozzles, the pumping head equals to static lift

plus nozzle pressure drop. The static lift equals to the overall height of tower, which is related to

L/G values will influence pump’s power. The nozzle pressure drop for induced draft tower is

around 0.02MPa to 0.05MPa in industry[8]

, which equals to 2 to 5m water height. Hence, the

nozzle pressure drop for this paper is taken to be 3m water height. Then, the pump’s power can

be calculated as[6]

:

Generally, the efficiency of pump is around 0.5 to 0.65. Then, the pump’s power with respect to

each L/G values can be calculated. For example, when L/G equals 0.75

Other results are listed in Appendix 7&8.

Capital cost of cooling tower

The capital cost of cooling tower includes the capital cost of tower, fill, fan and pump.

According to Turton, these capital cost can be calculated empirically. At ambient operating

pressure and using carbon steel construction, the purchased cost of the equipment can be

calculated from equation (12)[4]

:

where A is the capacity or size parameter of the equipment. The coefficients, maximum and

minimum values used in the correlation are given in that Turton’s book.[4]

For those equipments

16

whose capacity excess maximum values, the costs are calculated based on the maximum capacity

and multiplied by as compensation[4]

.

However, for different working pressures, materials and years, this cost will vary. Hence, in

order to estimate the cost exactly, Pressure factors, Material factor and Bare module factor

should be taken in consideration as an compensation. Then, the capital cost can be expressed as[4]

:

For tower and pumps:

For Fans with electric drives:

For tower packing:

For pressure factors:

The values of the constant , and are given in the book for different materials and type of

tower and pumps. is known for different types of fans and packing. The pressure factors

for all equipments are calculated to be 1, because the operation pressure is not very high which

leads to 0 values of all constant C.[4]

For different L/G values, capacities of different equipments

will be different that will influence the capital costs.

For example, when L/G equals 0.75, the volume of tower is which excess the

maximum values of capacity. Then the capital cost of tower is calculated as:

17

Considering the construction material for cooling tower should has a good resistance to rustiness

and corrosion at highly moist environment, referring to the industrial material of cooling tower,

stainless steel is chosen for this design though it has a higher price than carbon steel. Then:

Other capital costs of equipments are list in Appendix 8.

Total cost of cooling tower

Assuming 10 year and 8000 hours per year operation time, the total cost of overall cooling tower

can be estimated with respect to L/G values from 0.75 to 1.5. Data is listed in Appendix 8. The

relation between L/G values and total cost is represented on Figure 5.

It can be found that the lowest cost appear when L/G equals 1.2. Then, it can be determined that

the optimal design L/G is 1.2.

Step 5) Other Calculation

When L/G is 1.2, other details can be calculated easily.

For makeup water, the amount can be calculated by a empirical equations:[1][6]

Figure 5, L/G vs. total cost

18

where is makeup water, is circulation water, is evaporation loss, is drift loss and

is blown down. For this design of cooling tower, Newater is used as cooling water, because

Newater contains less amount of chlorate and salts which contributes to less corrosion and larger

cycles’ number (about 10). Besides, Newater is recommended by Singapore government for the

purpose of saving water resources. Then, makeup water is calculated as:

For pressure drop across the packing: [3][13]

For PN-11 type,

19

Details of Cooling Tower

Capacity 5400

Range 13 Relative

outlet

humidity

99% Air Flow

rate

1184.68

Density of

water

998.1

Approach 4.2 L/G 1.2 Pressure

Drop across

fill

66.4 Pa

Dry bulb

temperature

of air (inlet)

Effectiveness 75.58% KaV/L 1.967 Enthalpy of

air (inlet)

92.9

kJ/kg

Wet bulb

temperature

of air (inlet)

Cell width 11.54m Floor area 799.68 Enthalpy of

air (outlet)

158.20

kJ/kg

Relative

inlet

humidity:

80% No. of cells 6 Volume 15387.76 Fan power 235.37

kW

Cooling

water inlet

( ):

Tower Width 23.09m Water

Loading

6739.89

Pump power 502.07

kW

Cooling

water outlet

( ):

Tower Length 34.63m Air velocity

across

packing

1.42

Capital cost

Altitude (Z): 0 m Tower Height 19.24 m Density of

air at Fan

1.05

Operational

cost(10 year)

Heat load

Packed height 1.925m Dry bulb

temperature

of air

(outlet)

39.2 Total cost

20

Cell 11.54 m

Width 23.09 m

Length 34.63 m

Height 19.24 m

Height 19.24 m

Appendix

Appendix 1

For saturated air

Temperature( ) Hw(kJ/kg

30 99.6709

30.5 102.3102

31 105.0097

31.5 107.7712

32 110.5962

32.5 113.4866

33 116.444

33.5 119.4703

34 122.5674

34.5 125.7371

35 128.9816

35.5 132.3028

36 135.7028

36.5 139.1839

37 142.7482

37.5 146.3981

38 150.1359

38.5 153.9642

39 157.8854

39.5 161.9021

40 166.0171

40.5 170.2332

41 174.5532

41.5 178.9801

42 183.517

42.5 188.167

43 192.9335

43.5 197.8198

44 202.8295

44.5 207.9662

45 213.2337

Length 34.63m

Height 19.24m

Height 19.24m

Length 34.63m

Height 19.24m

Height 19.24m

Width 23.09m

22

Appendix 2

Temperature ( ) Ha (kJ/kg) Hw (kJ/kg) Hw-Ha (kJ/kg) 1/(Hw-Ha) (kg/kJ) NTU

30 92.9 99.6709 6.770901 0.147691

30.5 96.0395 102.3102 6.27066 0.159473 0.321447

31 99.179 105.0097 5.830707 0.171506 0.346369

31.5 102.3185 107.7712 5.452666 0.183397 0.371405

32 105.458 110.5962 5.138209 0.19462 0.395595

32.5 108.5975 113.4866 4.889054 0.204539 0.417720

33 111.737 116.444 4.706972 0.212451 0.436379

33.5 114.8765 119.4703 4.593782 0.217686 0.450138

34 118.016 122.5674 4.551361 0.219714 0.457739

34.5 121.1555 125.7371 4.581639 0.218263 0.458343

35 124.295 128.9816 4.686602 0.213374 0.451708

35.5 127.4345 132.3028 4.86830 0.205411 0.438258

36 130.574 135.7028 5.128841 0.194976 0.419004

36.5 133.7135 139.1839 5.470399 0.182802 0.395345

37 136.853 142.7482 5.895216 0.169629 0.368819

37.5 139.9925 146.3981 6.405602 0.156113 0.340889

38 143.132 150.1359 7.003938 0.142777 0.312789

38.5 146.2715 153.9642 7.692683 0.129994 0.285454

39 149.411 157.8854 8.474372 0.118003 0.259528

39.5 152.5505 161.9021 9.351621 0.106933 0.235396

40 155.69 166.0171 10.32713 0.096832 0.213241

40.5 158.8295 170.2332 11.40369 0.087691 0.193104

41 161.969 174.5532 12.58418 0.079465 0.174928

41.5 165.1085 178.9801 13.87158 0.07209 0.158602

42 168.248 183.517 15.26896 0.065492 0.143980

42.5 171.3875 188.167 16.7795 0.059597 0.130906

43 174.527 192.9335 18.40649 0.054329 0.119223

43.5 177.6665 197.8198 20.15332 0.04962 0.108782

44 180.806 202.8295 22.02352 0.045406 0.099444

44.5 183.9455 207.9662 24.02073 0.041631 0.091084

45 187.085 213.2337 26.14871 0.038243 0.083588

8.679205

23

Appendix 3

Temperature ( ) Ha (kJ/kg) Hw (kJ/kg) Hw-Ha (kJ/kg) 1/(Hw-Ha) (kg/kJ) NTU

30 92.9 99.6709 6.770901 0.147691

30.5 96.6674 102.3102 5.64276 0.177218 0.340017

31 100.4348 105.0097 4.574907 0.218584 0.414207

31.5 104.2022 107.7712 3.568966 0.280193 0.52197

32 107.9696 110.5962 2.626609 0.380719 0.691645

32.5 111.737 113.4866 1.749554 0.571574 0.996575

33 115.5044 116.444 0.939572 1.064315 1.711958

33.5 119.2718 119.4703 0.198482 5.03823 6.386313

34 123.0392 122.5674 -0.47184 -2.11937 3.054588

34.5 126.8066 125.7371 -1.06946 -0.93505 -3.19645

35 130.574 128.9816 -1.5924 -0.62798 -1.63572

35.5 134.3414 132.3028 -2.0386 -0.49053 -1.17053

36 138.1088 135.7028 -2.40596 -0.41563 -0.9483

36.5 141.8762 139.1839 -2.6923 -0.37143 -0.82366

37 145.6436 142.7482 -2.89538 -0.34538 -0.75014

37.5 149.411 146.3981 -3.0129 -0.33191 -0.70878

38 153.1784 150.1359 -3.04246 -0.32868 -0.6913

38.5 156.9458 153.9642 -2.98162 -0.33539 -0.69495

39 160.7132 157.8854 -2.82783 -0.35363 -0.72106

39.5 164.4806 161.9021 -2.57848 -0.38783 -0.77593

40 168.248 166.0171 -2.23087 -0.44826 -0.87496

40.5 172.0154 170.2332 -1.78221 -0.5611 -1.05629

41 175.7828 174.5532 -1.22962 -0.81326 -1.43827

41.5 179.5502 178.9801 -0.57012 -1.75402 -2.68666

42 183.3176 183.517 0.199361 5.016023 3.413685

42.5 187.085 188.167 1.082001 0.924213 6.216458

43 190.8524 192.9335 2.081089 0.480518 1.470051

43.5 194.6198 197.8198 3.200024 0.312498 0.829891

44 198.3872 202.8295 4.442324 0.225107 0.562604

44.5 202.1546 207.9662 5.81163 0.172069 0.415645

45 205.922 213.2337 7.311712 0.136767 0.323196

9.1758

24

Appendix 4

L/G NTU

0.4 1.293297

0.45 1.319627

0.5 1.347266

0.55 1.376323

0.6 1.406915

0.65 1.439176

0.7 1.473257

0.75 1.509326

0.8 1.547576

0.85 1.588224

0.9 1.631519

0.95 1.677749

1 1.727243

1.05 1.780386

1.1 1.837629

1.15 1.899501

1.2 1.966632

1.25 2.039775

1.3 2.11984

1.35 2.20794

1.4 2.30545

1.45 2.41409

1.5 2.536048

1.55 2.67415

1.6 2.832122

1.65 3.014988

1.7 3.22971

1.75 3.486246

1.8 3.799422

1.85 4.19243

1.9 4.70394

1.95 5.404212

2 6.437482

25

Appendix 5

26

Appendix 6

Type L/G m Ka/L NTU V

PN-1 1.5 0.295 0.5 0.240866 2.536048 10.52885

PN-2 1.5 0.236 0.47 0.195051 2.536048 13.00194

PN-3 1.5 0.288 0.7 0.216835 2.536048 11.69577

PN-4 1.5 0.459 0.73 0.341402 2.536048 7.428332

PN-5 1.5 0.276 0.49 0.226269 2.536048 11.20813

PN-6 1.5 0.689 0.69 0.520854 2.536048 4.869015

PN-7 1.5 0.36 0.66 0.275475 2.536048 9.206088

PN-8 1.5 0.558 0.58 0.441064 2.536048 5.749845

PN-9 1.5 0.243 0.52 0.196806 2.536048 12.88601

PN-10 1.5 0.666 0.7 0.50143 2.536048 5.05763

PN-11 1.5 1.152 0.66 0.88152 2.536048 2.876903

PN-12 1.5 0.331 0.63 0.256384 2.536048 9.891608

PN-13 1.5 0.282 0.52 0.228392 2.536048 11.10391

PN-14 1.5 1.01 0.8 0.730211 2.536048 3.473034

PN-15 1.5 0.814 0.79 0.590898 2.536048 4.291855

PN-16 1.5 0.99 0.45 0.824886 2.536048 3.074421

PN-1 0.75 0.295 0.5 0.340637 1.509326 4.430898

PN-2 0.75 0.236 0.47 0.270168 1.509326 5.586631

PN-3 0.75 0.288 0.7 0.352249 1.509326 4.28483

PN-4 0.75 0.459 0.73 0.566263 1.509326 2.665417

PN-5 0.75 0.276 0.49 0.317782 1.509326 4.749568

PN-6 0.75 0.689 0.69 0.840286 1.509326 1.796206

PN-7 0.75 0.36 0.66 0.435273 1.509326 3.467537

PN-8 0.75 0.558 0.58 0.659324 1.509326 2.289204

PN-9 0.75 0.243 0.52 0.282211 1.509326 5.348214

PN-10 0.75 0.666 0.7 0.814576 1.509326 1.852899

PN-11 0.75 1.152 0.66 1.392875 1.509326 1.083605

PN-12 0.75 0.331 0.63 0.396771 1.509326 3.804029

PN-13 0.75 0.282 0.52 0.327504 1.509326 4.608567

PN-14 0.75 1.01 0.8 1.271371 1.509326 1.187164

PN-15 0.75 0.814 0.79 1.021706 1.509326 1.477261

PN-16 0.75 0.99 0.45 1.126828 1.509326 1.339447

27

Appendix 7

L/G KaV/L

Packed

Height (m)

Packed

Volume( )

Total

Height (m)

Total

Volume

Width of

cell (m)

0.75 1.5093 1.0836 866.5354 18.4006 14714.5778 11.5447

0.80 1.5476 1.1594 927.1587 18.4764 14775.2011 11.5447

0.85 1.5882 1.2384 990.3550 18.5555 14838.3974 11.5447

0.90 1.6315 1.3211 1056.4646 18.6381 14904.5070 11.5447

0.95 1.6777 1.4079 1125.8672 18.7249 14973.9096 11.5447

1.00 1.7272 1.4993 1198.9914 18.8164 15047.0338 11.5447

1.05 1.7804 1.5961 1276.3268 18.9131 15124.3692 11.5447

1.10 1.8376 1.6987 1358.4378 19.0158 15206.4802 11.5447

1.15 1.8995 1.8082 1445.9820 19.1252 15294.0244 11.5447

1.20 1.9666 1.9254 1539.7330 19.2425 15387.7754 11.5447

1.25 2.0398 2.0516 1640.6105 19.3686 15488.6529 11.5447

1.30 2.1198 2.1880 1749.7192 19.5051 15597.7616 11.5447

1.35 2.2079 2.3364 1868.4017 19.6535 15716.4441 11.5447

1.40 2.3054 2.4989 1998.3099 19.8159 15846.3523 11.5447

1.45 2.4141 2.6780 2141.5046 19.9950 15989.5470 11.5447

1.50 2.5360 2.8769 2300.5958 20.1939 16148.6382 11.5447

L/G G (kg/h) G ( ) ( ) ( (kJ/kg) velocity(m/s)

0.75 7186320.0000 1852.4381 1.0776 35.8600 133.7135 2.2693

0.80 6737175.0000 1741.3860 1.0747 36.2700 136.4344 2.1275

0.85 6340870.5882 1643.2349 1.0719 36.6600 139.1553 2.0023

0.90 5988600.0000 1555.8283 1.0692 37.0300 141.8762 1.8911

0.95 5673410.5263 1477.8689 1.0664 37.4200 144.5971 1.7916

1.00 5389740.0000 1407.3629 1.0638 37.7700 147.3180 1.7020

1.05 5133085.7143 1343.9839 1.0609 38.1600 150.0389 1.6209

1.10 4899763.6364 1285.9578 1.0584 38.5000 152.7598 1.5473

1.15 4686730.4348 1233.1860 1.0557 38.8600 155.4807 1.4800

1.20 4491450.0000 1184.6782 1.0531 39.2000 158.2016 1.4183

1.25 4311792.0000 1140.0825 1.0506 39.5400 160.9225 1.3616

1.30 4145953.8462 1098.9487 1.0480 39.8800 163.6434 1.3092

1.35 3992400.0000 1061.0487 1.0452 40.2400 166.3643 1.2607

1.40 3849814.2857 1025.3551 1.0429 40.5300 169.0852 1.2157

1.45 3717062.0690 992.3678 1.0405 40.8500 171.8061 1.1738

1.50 3593160.0000 961.5328 1.0380 41.1600 174.5270 1.1347

28

Appendix 8

L/G Tower Capital($)

Packing

Capital($) Fan Capital($)

Pump

Capital($)

Fan

Power(kW)

Pump

Power(kW)

0.75 28061904.12 338495.46 1850898.75 280916.84 368.03 483.06

0.80 28131215.21 362135.59 1783501.44 281513.49 345.97 484.78

0.85 28203347.07 386784.43 1722488.06 282134.56 326.47 486.56

0.90 28278672.76 412575.59 1666914.95 282783.30 309.10 488.42

0.95 28357606.82 439658.16 1616285.15 283463.28 293.62 490.38

1.00 28440615.53 468200.59 1569567.86 284178.55 279.61 492.45

1.05 28528229.23 498395.23 1526767.42 284933.71 267.02 494.63

1.10 28621057.34 530464.03 1486868.14 285734.05 255.49 496.95

1.15 28719807.20 564665.62 1449951.90 286585.70 245.00 499.42

1.20 28825308.02 601304.44 1415456.96 287495.86 235.37 502.07

1.25 28938541.66 640742.47 1383242.11 288473.07 226.51 504.91

1.30 29060683.18 683414.82 1353078.18 289527.54 218.33 507.99

1.35 29193154.66 729850.45 1324883.28 290671.63 210.80 511.34

1.40 29337698.29 780700.55 1297959.15 291920.51 203.71 515.01

1.45 29496477.08 836777.83 1272740.96 293293.00 197.16 519.05

1.50 29672216.95 899112.28 1248863.25 294812.85 191.03 523.54

L/G Capital Cost(S$)

Operational

Cost(S$) Total Cost(S$)

0.75 38394260.57 17164942.95 55559203.53

0.80 38427144.90 16754481.16 55181626.06

0.85 38472903.32 16397177.00 54870080.32

0.90 38530990.34 16084583.73 54615574.07

0.95 38601494.36 15811718.56 54413212.92

1.00 38683922.38 15570837.13 54254759.51

1.05 38779194.43 15360910.19 54140104.62

1.10 38887085.37 15175149.91 54062235.27

1.15 39008920.61 15013536.72 54022457.33

1.20 39145428.34 14872541.74 54017970.07

1.25 39298131.63 14751279.32 54049410.95

1.30 39468779.91 14648574.26 54117354.17

1.35 39659739.23 14564276.65 54224015.87

1.40 39873160.20 14495210.80 54368371.00

1.45 40113355.75 14444551.84 54557907.59

1.50 40384619.20 14411566.90 54796186.11

29

Reference

[1] Jonny Goyal, Effective Thermal Design of Cooling Towers, Feb 2012, Chemical Engineering,

www.che.com.

[2] A.K.M Mohiuddin, K. Kant, Knowledge base for the systematic design of wet cooling towers.

Part 1:Selection and tower characteristics. Int J,Refrig.Vol 19.No. 1,pp 43-61,1996.

[3] A.K.M Mohiuddin, K. Kant, Knowledge base for the systematic design of wet cooling towers.

Part 11:Fill and other design parameters. Int J,Refrig.Vol 19.No. 1,pp 52-61,1996

[4] Richard Turton, Analysis, synthesis, and design of chemical processes, Chapter7&8, Upper

Saddle River, N.J. : Prentice Hall, c2009. 3rd ed.

[5] M.H.Panjeshali, A. Ataei, Application of an environmentally optimum cooling water system

design in water and energy conservation, Int. J. Environ. Sci. Tech., 5 (2), 251-262, Spring

2008, ISSN: 1735-1472

[6] Charles G. Moyers, Glenn W. Baldwin, Chemical Engineering Handbook, Section 12

Psychrometry, Evaporative Cooling, and Solids Drying,2009.

[7] Cooling towers, In: Energy Efficiency in Electrical Utilities. Chapter 7, pg 135 -

151. 2004, Bureau of Energy Efficiency, Ministry of Power, India.

[8] S.C Krane, Optimal spray patterns for counter flow cooling towers with structured packing,

Science Direct, Applied Mathematical Modeling 31 (2007) 676–686.

[9] JEAN-PIERRE LIBERT, EVAPTECH, INC. DESIGN AND OPERATION OF A

COUNTERFLOW FILL AND NOZZLE TEST CELL: CHALLENGES AND SOLUTIONS,

Presented at the 2007 Cooling Technology Institute Annual Conference Corpus Christi, TX -

February 4-7, 2007.CTI

[10] R.V. Rao,V.K. Patel, Optimization of mechanical draft counter flow wet-cooling tower

using artificial bee colony algorithm, Energy Conversion and Management 52 (2011) 2611–2622

30

[11] Lu Lu, Research Associate, A UNIVERSAL ENGINEERING MODEL FOR COOLING

TOWERS,2009.

[12] ASHRAE, ASHRAE Handbook—HVAC Systems and Equipment, American Society of

Heating, Refrigerating, and Air-Conditioning Engineers Inc., 1996.

[13]Cooling Tower Thermal Design Manual, Daeil Aqua Co. Ltd,2003.

[14]Optimizing Cooling Tower Performance, Energy Service, 1998.

[15] Robert Burger, Cooling Tower Technology, Burger Associate, Inc., Dalla,Texas, 75 234,US.