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In this Thesis I will try to understand the concept associated with cooling towers and model a laboratory sized cooling tower in a software package called Engineering Equation Solver (EES). An example of system modelling is presented in this progress report, along with the comparison of a set of results with an experimental data from P.A Hilton Model H892 Bench top cooling tower with a maximum of 9% error. A user interface is also modelled to simulate off-design performance rather than conducting experiments. It also allows you to do additional scenarios that cannot be practically being done in lab, like Relative humidity, etc.
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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.