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The investigation of cooling tower packing in various
arrangements
H.R. Goshayshi*, J.F. Missenden
School of Engineering Systems and Design, South Bank University, London, SE1 0AA, UK
Received 10 August 1998; accepted 24 January 1999
Abstract
The eect of form with corrugated packing on mass transfer and pressure drop characteristics in
atmospheric cooling towers has been studied experimentally. The results showed that the mass transfer
coecient decreased with increase in packing pitch and increase in the ratio of rib pitch to rib height.
Friction factors were expressed by a dimensional equation which included pitch and distance between
the packings, for both smooth and rough surfaces. From these results, the relationship between packing
mass transfer coecient and pressure drop was deduced. The correlations were veri®ed with additional
experimental data taken with 1.1 < P/D < 1.70 and 1Ep/eE5. This provides a useful semi-
experimental relation, in an area generally lacking in design and performance data. # 1999 Elsevier
Science Ltd. All rights reserved.
Keywords: Cooling towers; Packing; Pressure drop; Mass transfer
1. Introduction
Heat and mass transfer between a falling liquid ®lm along a vertical wall and upward
¯owing air contacting directly with the ®lm is an important and interesting phenomenon in
industrial apparatus such as cooling towers. While 96% of the cooling towers use PVC packing
with smooth and cross ribbing, no data on the ¯ow of liquid over a ¯at vertical wall with cross
ribbing have been published. Only some of the features of their operation in contact heat
exchangers have been investigated [1±5]. Major aspects that remain to be studied include: the
Applied Thermal Engineering 20 (2000) 69±80
1359-4311/00/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.
PII: S1359-4311(99)00011-3
www.elsevier.com/locate/apthermeng
* Corresponding author. Tel.: +44-171-815-7639; fax: +44-171-815-7699.
geometry and layout of the main corrugation with and without the cross ribbings, the pattern
of ¯ow of the liquid ®lm and interaction between phases. In this paper the mass transfer and
pressure drop characteristics of many types of corrugated packing, including smooth and rough
surface corrugated packings, are investigated, and the relationship between packing mass
transfer coecients and pressure drops is discussed. Mass transfer performance of rough
corrugated packing is increased by 1.5 to 2.5 times the smooth packing values, but the pressure
drop of packings also increases with the increase in heat transfer performance.
2. Experimental apparatus and procedure
The experimental apparatus for the heat transfer experiments consisted of a counter¯ow
forced draft cooling tower, as shown in Fig. 1. Water stored in a tank at the base was pumped
into the spray nozzles. The supply water velocity was regulated by a valve. The cross sectional
test area was A= 0.15 0.15 m. Inlet and outlet air and water temperatures were measured
by mercury in glass thermometers with a range of 0±508C and an accuracy of 0.2 K. Packing
pressure drop was measured by an APM 2000 (0±2000 Pa) micromanometer with an accuracy
of21% FSD (i.e. maximum of 1.2 Pa error in our measurements). Measurements of mass
transfer and pressure drop were carried out in the steady state. The mass transfer coecients
Nomenclature
a pack density (surface area per unit volume) (m
ÿ1)
D distance between the cooling tower packing (rib) (mm)
e height of roughness element (mm)
G ¯ow rate (air) (kg s
ÿ1)
G' mass ¯ux (air) (kg m
ÿ2 s
ÿ1)
E height of corrugation (mm)
L ¯ow rate (water) (kg s
ÿ1)
L' mass ¯ux (water) (kg m
ÿ2 s
ÿ1)
k mass transfer coecient (kg m
ÿ2 s
ÿ1)
Nu Nusselt number
p distance between repeated ribs (mm)
P pitch of packing (see Figs. 3 and 4) (mm)
Pr Prandtl number
Z packed height (m)
Dp pressure drop (Pa)
Rew water Reynolds number=2L'D/mw
ra air density (kg m
ÿ3)
ua air velocity inside the packing (m s
ÿ1)
uw water velocity inside the packing (m s
ÿ1)
y angle of inclination of cross ribbing with the horizontal (8)
70
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