FREON-WATER HEAT TRANSFER IN PLATE HEAT EXCHANGERS

Abstract

An experimental study on single and two phase heat transfer and friction characteristics for R-123 inside a plate heat exchanger (PRE) was conducted.

Single phase heat transfer and friction factor correlations were obtained for upflow and downflow conditions. There is no apparent distinction in heat transfer coefficient between the two configurations as seen from the heat transfer correlations derived for the PHE under study:

for upflow, Nu = 0.111 Re 0.8026 Pr 0.333

and for downflow, Nu = 0.0938 Re 0.8374 Pr 0.333

However, the friction factor during single phase downflow in a PHE is considerably higher than that for upflow due to effects of gravitational acceleration. The single phase friction factor correlations derived for the PHE under study are:

for upflow, f = 8.049 Re -0.1038

and for downflow, f = 771.43 Re -0.6371

In evaporation and condensation processes, the heat transfer coefficient correlations have been established in a wide range of operating conditions of mass flux, vapor quality, heat flux and saturation pressure. The evaporation process was found to b substantially more efficient than condensation. The heat transfer coefficient fo evaporation was correlated using the dimensionless parameters of Ruquid, Martinell parameter and Boiling number. The correlation derived is: Ruquid = 0.0034 Xtt.Bo -0.8492

In condensation, the dimensionless parameters applied are Rliquid and Martinelli parameter only and the correlation derived is:

R liquid = O.9704 Xtt.-0.5224 The results obtained from this study show that the performance of the PHE with the new refrigerant, R123, can be ascertained with correlations used to predict its performance with other existing fluids. This is very encouraging in view of the increasing demand for new environmental-friendly refrigerants which will replace the older ones, soon to be phased out.