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International Heat Transfer Conference 6

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

EFFECT OF WATER SPRAYS ON HEAT TRANSFER OF A FIN AND TUBE HEAT EXCHANGER

Dale R. Tree
Brigham Young University Provo, UT 84602 USA; Ray W. Herrick Laboratories, School of M.E., Purdue University, W. Lafayette, IN 47907 USA

V.W. Goldschmidt
Ray W. Herrick Laboratories, School of M.E., Purdue University, W. Lafayette, IN 47907 USA

R.W. Garrett
Ohio College of Applied Science, Cincinnati, OH 45210 USA

E. Kach
Caterpillar Tractor, Mossville, IL 61552 USA

Abstract

This study examined the performance of a fin and tube heat exchanger while wetted bу water sprays of different mass flux and drop diameters while air was blown across it. The spray is characterized bу its arithmetic mass mean diameter and for analytical purposes is assumed to be homogeneous as well as spatially uniform. The three drop diameters examined were 64, 440 and 3300 microns. The mass fluxes used were 10, 20 and 30 gm/sec (1.32, 2.64, 3.96 lbm/hr). Dry core measurements where there was no mass flux of spray water were also recorded. The dimensionless parameter, Nusselt number, was a measure of the performance of the heat exchanger.

The hydraulic Reynolds numbers of the test coil ranged from 340 to 670. The hydraulic Reynolds number was defined as: ReDH = 4 maDH/Aeµ. The frontal velocities of the air stream were in the range 0.8 to 2.3 m/sec (150 to 450 fpm). The inlet dry bulb/ wet bulb temperature of the free stream air was kept constant at 35.3°C/24.2°C (95°F/75°F) or 40% relative humidity.

The major experimental problem was production of a homogeneous spatially uniform water spray with a predetermined drop diameter. In this work three different kinds of generators were considered.

The mass rate of flow of the sprayed water had the greatest effect on the heat transfer enhancement. Drop diameter had a small effect in the ranges studied but it is suspected that very small drop sizes (below 40 microns) would have less effect since it was predicted that they would completely evaporate, cooling only the air before reaching the condenser. Spatial uniformity plays an important part in the evaporation process. In fact, the difference in uniformity of any two sprays could easily cancel any effects due to drop diameter. Theoretically, drop diameter has an effect on total evaporation rate of a spray with mass flux larger than those studied but spatial uniformity dominates in the actual case.

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