Heat transfer and pressure drop during HFC refrigerant saturated vapour condensation inside a brazed plate heat exchanger

摘要

This paper presents the heat transfer coefficients and the pressure drop measured during HFC refrigerants 236fa, 134a and 410A saturated vapour condensation inside a brazed plate heat exchanger: the effects of saturation temperature (pressure), refrigerant mass flux and fluid properties are investigated. The heat transfer coefficients show weak sensitivity to saturation temperature (pressure) and great sensitivity to refrigerant mass flux and fluid properties. A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 20 kg/m~2s that corresponds to an equivalent Reynolds number around 1600-1700. At low refrigerant mass flux (G_r < 20 kg/m~2s) the heat transfer coefficients are not dependent on mass flux and are well predicted by the Nusselt [20] analysis for vertical surface: the condensation process is gravity controlled. For higher refrigerant mass flux (G_r > 20 kg/m~2s) the heat transfer coefficients depend on mass flux and are well predicted by Akers et al. [21] equation: forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 25-30% increase for a doubling of the refrigerant mass flux.rnThe frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on mass flux.rnHFC-410A shows heat transfer coefficients similar to HFC-134a and 10% higher than HFC-236fa together with frictional pressure drops 40-50% lower than HFC-134a and 50-60% lower than HFC-236fa.