Theoretical Investigation on Thermal Performance of New Structure Closed Wet Cooling Tower

ABSTRACT

Thermal performance of closed wet cooling tower (CWCT) with packing is analyzed using experiments and numerical simulations. The effect of cooling water flow direction on the performance is discussed. The results show that the packing plays an important role in improving the cooling effect of the CWCT. Under the same operating conditions, the cooling water outlet temperature of CWCT with packing is lower than that of CWCT without packing between 0.6°C and 1.5°C the cooling efficiency of CWCT with packing is higher than that of CWCT without packing between 6.0% and 14.8%. The concurrent cooling water flow direction results in more uniform temperature differences between cooling water and the spray water, which can benefit the cooling water outlet temperature 0.3–0.7°C and the cooling efficiency 3.0–9.5%.

Nomenclature

A	=	area, m2
Cp	=	specific heat constant pressure, J/(kg⋅K)
CWCT	=	closed wet cooling tower
d	=	diameter, m
h	=	heat transfer coefficient, W/(m2·K)
hd	=	mass transfer coefficient, W/(m2·K)
i	=	enthalpy, J/kg
K	=	overall heat transfer coefficient of tube section, W/(m2·K)
Lef	=	Lewis number, dimensionless
m	=	mass flow rate, W/(m·K)
N	=	tube row number
p	=	atmospheric pressure, Pa
ps	=	saturation pressure of steam at the spray water temperature, Pa
Q	=	heat transfer rate, W
Re	=	Reynolds number, dimensionless
S	=	cross-sectional area of tower, m2
T	=	temperature, K or °C
Pr	=	Prandtl number, dimensionless
U	=	evaporation heat coefficient, W/(m·k)
V	=	packing volume, m3
w	=	humidity ratio of air, kg(water vapor) /kg (dry air)
z	=	height of closed wet cooling tower, m

Greek symbols

α	=	heat transfer coefficient of packing, W/(m2·K)
β	=	mass transfer coefficient of packing, kg/(m2·s)
λ	=	thermal conductivity, W/(m·K)
η	=	thermal efficiency, dimensionless
γ	=	latent heat of evaporation, J/kg
Γ	=	spray water flow rate per unit breadth, kg/(s·m)

Subscripts

a	=	air, or basic on air-side area
f	=	cooling water
i	=	inlet, or inside
l	=	latent heat
o	=	outlet, or outside
s	=	sensible heat
t	=	tube wall
v	=	vapor
w	=	spray water
wb	=	wet bulb
0	=	spray water temperature of 0°C

Superscripts

*	=	saturated
−	=	average

Additional information

Notes on contributors

Yasu Zhou

Yasu Zhou is a Professor of Heating, Ventilation and Air Conditioning at the Donghua University, Shanghai, China. She received her M.Sc. degree from the Donghua University, and her Ph.D. degree from the Tongji University, Shanghai, China. She has been teaching at the Donghua University since 1989 except for one year as a researcher spent at the Chalmers University of Technology, Sweden. She has been the Vice Dean of College of Environmental Science and Engineering in Donghua University for nine years. Her research contributions are in the field of building energy efficiency. She is currently working on enhanced heat transfer and condensation in heat exchangers.

Xun Zhu

Xun Zhu is a graduate school student in Donghua University, Shanghai, China. She majors in heating, ventilation and air conditioning. Her tutor is Prof. Yasu Zhou. She is currently working on closed wet cooling tower with packing. She developed a theoretical model considering heat and mass transfer by using MATLAB to predict the thermal performance characteristics of closed wet cooling towerwith packing.

Xiao Ding

Xiao Ding is an engineer at the Saic Motor Corporation Limited Commercial Vehicle Technical Center, Shanghai, China. He is mainly engaged in the design of heating, ventilation and air conditioning for commercial vehicles, provides alternative design solutions, analysis and ensures the performance of air conditioning system can meet customer requirements.