COOLING TOWER MODELLING IN EES

Theses Presentation

DT 022/4

SHIYAS BASHEER Supervisor: ANTHONY REYNOLDS

Objectives

Study on Cooling TowersRecent developmentsCreate a mathematical modelImplement it on EES (Engineering Equation Solver)Verify the resultsCreate a user interfaceSensitivity analysis

Implementation

Mathematical modelling (governing equations)

Input· variables· fixed

parameters

ResultsDatabase of

thermodynamic properties

Write the code

Run the program

Engineering Equation Solver

Equation solving programUseful in thermodynamic and heat transfer problemsEquations entered in any orderHigh accuracyGraphical Input/outputNo real programming

Cooling Tower

Extract heat Reduce temperatureEmit to atmosphere

Schematic diagram of a cooling tower(Energy, 2011)

Types of Cooling Towers

Wet Cooling towerOnce through cooling towerDirect dry coolingIndirect dry coolingWet dry cooling tower

Hilton H892

Theory

Assumptions

Steady stateRelative Humidity – 100%Negligible Kinetic and potential energyFully saturated Ambient temperature of air going in

Control Volume

Control Volume

Mathematical Model

Mass Balance∑𝒊𝒏

�̇�=¿∑𝒐𝒖𝒕

�̇�¿

Conservation of mass for water:

Conservation of mass for air:

Mathematical Model

Energy Balance�̇� 𝒊𝒏=�̇�𝒐𝒖𝒕

At the water side:

On the moist air side :

Mathematical Model

Mass Balance

∑𝒊𝒏

�̇�=¿∑𝒐𝒖𝒕

�̇�¿

Conservation of mass principle

Mathematical Model

At the mixing point:

Energy Balance

�̇� 𝒊𝒏=�̇�𝒐𝒖𝒕

Implementation in EES

35 Equations

ResultsExperimental Modelled

TEST No. Units 1 2 3 4 1 2 3 4

Air inlet Dry Bulb (t1) oC 19 19 19.4 19.7 19 19 19.4 19.7

Air inlet Wet Bulb (t2) oC 15.6 15.4 15.8 16.5 15.34 15.34 15.7 15.97

Air Outlet Dry Bulb (t3) oC 16.8 18.4 20.5 23 16.02 18.72 21.44 23.81

Air Outlet Wet Bulb (t4) oC 16 18 20.4 23 15.85 18.54 21.24 23.6

Water Inlet Temperature (t5) oC 17 21.6 27.2 32.7 16.84 21.47 27.09 33.34

Water Outlet Temperature (t6) oC 16.4 18.6 21.3 23.9 16.28 18.7 21.5 24.0

Cooling Load (Q) kW 0 0.5 1 1.5 0 0.5 1 1.5

Make-up Quantity (me) kg 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25

Time Interval (y) s 600 600 600 600 600 600 600 600

Water Flow Rate (Mw) g/s 40 40 40 40 40 40 40 40

CALCULATIONS  

Air Flow Rate (ma) kg/s 0.05728 0.05728 0.05728 0.05728 0.05728 0.05728 0.05728 0.05728

Evaporation Rate kg/s 0.00049 0.00049 0.00049 0.00049 0.00049 0.00049 0.00049 0.00049

Make-up Rate kg/s 9.6E-07 9.6E-07 9.6E-07 9.6E-07 9.6E-07 9.6E-07 9.6E-07 9.6E-07

   

Rate of Make-up Quantity (mE) kg/s 0.00042 0.00042 0.00042 0.00042 0.00042 0.00042 0.00042 0.00042

Approach to Wet Bulb oC 0.8 3.2 5.5 7.4 0.88 3.36 5.8 7.7

Cooling Range oC 0.6 3 5.9 8.8 0.56 2.77 5.59 9.34

Verification of Results

15 16 17 18 19 20 21 22 23 24 2515

16

17

18

19

20

21

22

23

24

25

f(x) = 1.02917321596982 x − 0.514922980194907R² = 0.99917774027959

Comparison of Water outlet temperature 0C

Experimental

Mod

elle

d

Verification of Results

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10

f(x) = 1.0631342791158 x − 0.298839326954802R² = 0.993255380489199

Comparison of Cooling Range 0C

Experimental

Mod

elle

d

Overall Difference

1 2 3 4

-20.00%

-10.00%

0.00%

10.00%

20.00%

30.00%

40.00%

-0.74%

0.53% 0.93% 0.42%

9.09%

4.76% 5.17%3.90%

-7.14% -8.30%-5.55%

5.78%

-0.95% -0.61% -0.41%

1.92%

-0.95%

2.91% 3.95%2.54%

Difference Plot

Water Outlet Temperature Approach to Wet bulb Temperature Cooling RangeWater Inlet Temperature Air Outlet Wet-bulb Temperature

Dif

fere

nce

Bet

wee

n E

xper

imen

tal a

nd

Mod

elle

d D

ata

Overall Difference

1 2 3 4 5

-30%

-20%

-10%

0%

10%

20%

30%

40%

-5% -6%-4% -4% -4%

20%

7%

32%

-2% -2%-2%

7%

-5%-3%

36%

-14%

-7%

-23% -23%

4%

-4%-1%

-4% -3%

1%

Difference Plot

Water outlet temperature Approach to wet bulb Cooling Range Air outlet wet bulb Water inlet temperature

Dif

fere

nce

bet

wee

n e

xper

imen

tal a

nd

mod

elle

d d

ata

Sensitivity Analysis

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60

5

10

15

20

25

30

35

40

Relationship between cooling load and water inlet temperature

EES Results Linear (EES Results)Actual Results Linear (Actual Results)

Cooling Load kW

Out

let w

ater

tem

pera

ture

0C

Sensitivity Analysis

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60

5

10

15

20

25

30

35

40

Relationship between cooling load and range

EES Water outlet temperature Linear (EES Water outlet temperature) EES Water inlet temperatureLinear (EES Water inlet temperature) EES Wet bulb temperature Linear (EES Wet bulb temperature)Actual water outlet temp Linear (Actual water outlet temp) Actual water inlet temperatureLinear (Actual water inlet temperature) Actual wet bulb temperature Linear (Actual wet bulb temperature)

Cooling Load kW

Tem

pera

ture

0C Cooling Range

Sensitivity Analysis

0 0.5 1 1.5 2 2.5 30

2

4

6

8

10

12

14

16

18

Relationship between Air velocity and approach

EES ResultsActual Results

Air Velocity m/s

Ap

pro

ach

to

wet

bu

lb t

emp

erat

ure

0C

User Interface

Conclusion and Future Work

All objectives metLow simulation timeHigh accuracyInvestigate more into the errorsInvestigate the equationsAdd Merkel’s Theory of evaporation

Thank you

Reference 2013a. ACHE [Online]. Available: http://www.thermopedia.com/content/663/.

2013b. EES: Engineering Equation Solver | F-Chart Software : Engineering Software [Online]. Available: http://www.fchart.com/ees/.

2013c. Natural Draft Cooling Towers | Hamon Group [Online]. Available: http://www.hamon.com/en/cooling-systems/wet-cooling-systems/natural-draft-cooling-towers/natural-draft/.

BURGER, R. 1994. Cooling Tower Technology. Maintenance, Upgrading and Rebuilding. United States of America: The Fairmont Press, Inc. .

ENERGY, U. S. D. O. 2011. Cooling Towers: Understanding Key Components of Cooling Towers and How to Improve Water Efficiency. In: ENERGY (ed.).

HEATING, A. I. O. A. C. R. A. 2009. Types of Cooling Towers In: Selecting a Cooling Tower Level 1 – Participant Guide Version 1.0.

TAWNEY, R., KHAN, Z. & ZACHARY, J. 2005. Economic and performance evauation of heat sink Options in combined cycle applications. Journal of engineering for Gas Turbine and Power, 127, 397-403.

Cooling Tower Technical Site of Daeil Aqua Co., L. (n.d.). Cooling Tower Thermal Design Manual. Retrieved from http://myhome.hanafos.com/~criok/english/publication/thermal/thermal12eng.htmlLtd, P. H. (2003, February). Experimental operating and maintanence manual.