HEAT TRANSFER AND PRESSURE DROP DURING HFC-134a CONDENSATION INSIDE A COMMERCIAL BRAZED PLATE HEAT EXCHANGER

摘要

This paper presents the experimental tests on HFC-134a condensation inside a commercial brazed plate heat exchanger: the effects of refrigerant mass flux, saturation temperature and vapour super-heating are investigated. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop.At low refrigerant mass flux (＜ 20 kg/m2s) the heat transfer coefficients for saturated vapour are not dependent on mass flux and are well predicted by the Nusselt (1916) analysis for vertical surface: the condensation process is gravity controlled. For higher refrigerant mass flux (＞ 20 kg/m2s) the heat transfer coefficients depend on mass flux and are well predicted by the Akers et al. (1959) equation: forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 30% increase for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are 8 - 10% higher than those of saturated vapour. The heat transfer coefficients show weak sensitivity to saturation temperature.The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on the refrigerant mass flux.