IPASJ International Journal of Mechanical Engineering (IIJME)
Web Site: http://www.ipasj.org/IIJME/IIJME.htm
Email: [email protected]
ISSN 2321-6441
A Publisher for Research Motivation........
Volume 3, Issue 1, January 2015
Thermal Performance Analysis of Natural
Draft Cooling Tower Simulation using CFX
Priyank V.Dave
Parul Institute of Technology, Limda, Vadodara-391760, Gujarat, India
ABSTRACT
Cooling tower plays a crucial role in process and power plants. The present work is focused on thermal calculations, analysis
and performance of natural draft cooling tower (NDCT) .The optimum design of cooling tower is a basic necessity in the
improvement of the overall efficiency of plant. The numerical modelling and performance investigation is done in detail to
study several aspects like consideration of design and operating conditions .The performance investigation is done with a
simplified numerical analysis techniques using Computational Fluid Dynamics (CFD) Here in cooling Tower throat height is
considered in numerical analysis for various thermal operating parameters (Range, Approach, Cooling Efficiency, losses,
effectiveness).For that varying throat height in CFD and considering their effects, ANSYS-CFX is considered for whole
numerical analyzing part and optimum throat height is investigated. The realistic performance of the system is possible to
predict with proper boundary conditions by using CFD tools.
Keywords:- Cooling Tower, Thermal Approach, Range, Model Simulation
1. INTRODUCTION
In Natural Draft Cooling Tower, there are no mechanical equipments such like fans & blowers. So, there is less
vibration and less noise as compared to Mechanical Draft Cooling Tower. Also as there are no mechanical parts, the
maintenance cost is low. In Cooling Towers, the warm water is cooled by means of evaporation. The water which flows
from the spray nozzles come in direct contact of air causing some of the water droplets to evaporate. The evaporating
water absorbs the latent heat of evaporation from the remaining water and the air takes away the sensible heat of water.
Hyperboloid (hyperbolic) Cooling Towers have become the design standard for all natural draft Cooling Towers
because of their structural strength and minimum usage of material. The hyperboloid shape also aids in accelerating the
upward convective air flow, improving cooling efficiency. J.C. Kloppers, D.G. Kroger [1] and N. Williamson, M.
Behnia developed numerical models to investigate the mechanism of the cooling tower. In that varying height of air
drawn to the tower and considering its effect on cooling range. M. Goodarzi[6] reported successful modeling of a
cooling tower under cross wind condition using the Computational Fluid Dynamics (CFD) simulation to predict the
performance which was close to that observed experimentally. YANG Xiang-liang [3] discussed the numerical
simulation of flow fields in a natural draft wet-cooling tower of Heze Power Plant in China. Ghassem Heidarinejada
et.al. [5] discussed regarding numerical simulation of counter-flow wet-Cooling Towers.
2. EXPERIMENTAL DATA OF COOLING TOWER
Table 1: Cooling Tower Input Data
Input Data
Parameters
Symbol
Value
Inlet Temperature of Water
T1
42°C
Outlet Water Temp.
T2
33°C
WBT
28°C
Volume of circulating water in cooling tower
V
30000 m3 / hr
Inlet Temperature of Air
Ta1
32°C
Outlet Temperature of Air
Ta2
38°C
Relative Humidity
Φ
55%
Evaporating Loss
EL
1.44%
Wet Bulb Temp.
Volume 3, Issue 1, January 2015
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IPASJ International Journal of Mechanical Engineering (IIJME)
Web Site: http://www.ipasj.org/IIJME/IIJME.htm
Email: [email protected]
ISSN 2321-6441
A Publisher for Research Motivation........
Volume 3, Issue 1, January 2015
Draft Loss
DL
0.01%
Stack Height for Cooling Tower
H
5.65m
From the input data regarding useful thermal calculations made and regarding values is in Table 2.
Table 2: Cooling Tower Thermal Calculations
Equations
Terms
Results
CTa= Tw2 - WBT
Approach
5° C
CTR =T1 – T2
Range
9° C
DL=0.20 x Mw1 / 100
Drift Losses
60000kg. / hr
WL=0.005 x Mw1
Windage Losses
150000kg. / hr
EL =0.00085 x 1.8x Mw1 (T1 – T2)
Evaporation Losses
408457kg. / hr
BL =EL / (Cycles – 1)
Blow down losses
204228.5kg./ hr
ηc =( T1 – T2 ) / ( T1 – WBT )
Efficiency
65%
L/G
L/G Ratio
1.29
v
Volume of Air Required
21147672 m3/hr
Ma
Mass of Air Required
The Quantity of Make-Up
Water
Total demand
25116000 Kg / hr
M
mak
NTU
2338m3/hr
1.15
3. SIMULATION PROCEDURE
3.1 Mesh adaption & Grid Independency Test:
As tetrahedral mesh is considered due to it has three nodes per element which is less as compare to quadrilateral mesh
so simulation procedure is carried out much faster and for every case grid independency test is carried out. The CFX
software allows you to refine your mesh automatically as the solution to your CFD calculation is obtained. This helps to
ensure that a fine mesh is used where the solution is changing most rapidly. The set-up for Mesh Adaption takes place
in the CFX-Pre software, not in CFX-Mesh. Mesh Adaption can be used to improve a reasonable solution; it cannot be
used to produce good solutions from an initial poor quality mesh, so by that we can still generate a reasonable mesh
After modeling and meshing in CFX-PRE boundary conditions are assigned . Single change is made in the dimension
which is increasing the throat height by 1 meter so taken into account case of at the throat height 92.12m, by changing
the throat height it affects on various thermal parameters (Range, Approach, Cooling efficiency) by providing same
boundary conditions and same simulation procedure is followed as in the case of throat height (90.12m) and results are
observed. The effects of turbulence were modeled using the standard k-ε turbulence model. To make the simulation
time economical, wall function is used to resolve the wall flows. There are several methods of discretizing a given
differential equation, but finite volume is used in ANSYS-CFX. The finite volume method is a numerical method for
solving partial differential equations that calculate the value of conserved variables averaged across the volume.
3.2 Result Analysis:
Resultant Graphs for Different Throat Height
Figure 1 Cooling Range Vs Throat Height of Cooling Tower
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IPASJ International Journal of Mechanical Engineering (IIJME)
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Volume 3, Issue 1, January 2015
As shown in the figure.1 at four different heights readings are taken. For this their respected cooling range is taken into
account at throat height 91.12 m height cooling range becomes highest which is 15k.So as throat height (1 meter) is
increased from the original throat height cooling range gets increased by 15%. As throat height range is increased
further 1 m (92.12m),the cooling range gets reduced as seen in the graph. That means further increment in throat
height cooling range gets decreased so the optimum throat height is 91.12m
Figure 2 Cooling Approach Vs Throat Height of Cooling Tower
In cooling Tower normally as lower the approach the better the cooling tower performance. As shown in Graph at four
different heights readings are taken. For that their respective cooling approaches are taken considered. At throat height
91.12 m cooling approach is minimum which gives better cooling efficiency.
Figure 3 Effectiveness Vs Throat Height of Cooling Tower
As shown in Figure 3 throat height versus cooling tower effectiveness is shown, In which particularly at 90m throat
height which is reference or original throat height, effectiveness is near about 0.7 .But through Numerically increment
of 1meter in throat height of model, which gives cooling tower effectiveness 0.80 which is maximum .
Table 3: Resultant Table for Varying Different Throat Heights
Throat
Height
(m)
90.12
89.12
91.12
92.12
Water Inlet
Temp (K)
Water Outlet
Temp (K)
WBT
(K)
Range
(T1T2)
Approach (T2WBT)
Efficiency(n)
(%)
315
315
315
315
302.5
303
300
305
298
298
298
298
12.5
12
15
10
4.5
5
2
7
70
64
81
58
Volume 3, Issue 1, January 2015
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IPASJ International Journal of Mechanical Engineering (IIJME)
A Publisher for Research Motivation........
Volume 3, Issue 1, January 2015
Web Site: http://www.ipasj.org/IIJME/IIJME.htm
Email: [email protected]
ISSN 2321-6441
4.CONCLUSION
As cooling range increases and approach decreases this two parameters are directly related with cooling efficiency so at
throat height at 91.12m cooling efficiency is almost near to 80% so 10to12% increment in cooling efficiency as
compare to original throat height 90.12m. The CFX simulations are performed to study the contribution of the cooling
tower on the overall performance of the power plants. For that in improvement in cooling tower operating parameters
case should be taken throat height for the evaluation of better performance of thermal parameters. In which at throat
height 91.12m 10 to 12% improvement in the cooling efficiency and 12 to 14% improvement in cooling range is
observed.
References
[1] J.C. Kloppers,D.G. Kroger, , “Influence of Temperature Inversions on Wet-Cooling Tower Performance”, Applied
Thermal Engineering vol25,2005 , pp. 1325–1336.
[2] A. Fouda, Z. Melikyan “A Simplified Model for Analysis of Heat and Mass Transfer in a Direct Evaporative
Cooler” applied thermal engineering, vol31, 2010, pp. 932-936.
[3] YANG Xiang-liang ,Heze Power Plant, China, “Numerical Simulation Of Flow Fields In A Natural Draft WetCooling Tower*”Hydrodynamics,vol 19,2007, pp. 762-768
[4] N. Williamson, M. Behnia and S. Armfield “Numerical Simulation of Heat And Mass Transfer In a Natural Draft
Wet Cooling Tower” 15 Australian fluid mechanics conference,13-17Dec2004
[5] Ghassem Heidarinejada, Maryam Karamia, Shahram Delfani, Tarbiat Modares University “Numerical Simulation
of Counter-Flow Wet-Cooling Towers” vol 32,2009, pp. 996-1002
[6] M. Goodarzi, Bu-AliSinaUniversity, “A Proposed Stack Configuration for Cooling Tower to Improve Cooling
Efficiency Under Cross Wind”, wind engineering and aerodynamics.
[7] Hamid Saffari ,S.M. Hosseinnia, “Two-Phase Euler-Lagrange CFD Simulation of Evaporative Cooling In A Wind
Tower” vol41,2009, pp.991-1000.
[8] Kern, “Process Heat Transfer”, 3 rd Edition
[9] Walker W.H, W.K.Lewis, W.H. Adams, “Principle of chemical engineering” Mc- Graw hill publication, 3 rd
Edition
[10] Kern “Cooling tower performance, 2 nd Edition
[11] ANSYS-CFX tutorial guide.
AUTHOR
Priyank Dave has received bachelor of engineering degree in Mechanical Engineering From Atimya
Institute of Technology & Science in 2009 and Master of Engineering in Thermal engineering in 2011
from Parul Institute of Engineering & Technology. He is working as an Assistant Professor in Parul
Institute of Technology in mechanical Department Since 2011.
Volume 3, Issue 1, January 2015
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