Heat Transfer and Pressure Drop During Hydrocarbon Refrigerant Vaporisation Inside a Brazed Plate Heat Exchanger

This paper presents the experimental heat transfer coefficients and pressure drop measured during HC-600a (Isobutane), HC-290 (Propane) and HC-1270 (Propylene) vaporisation inside a small brazed plate heat exchanger: the effects of heat flux, refrigerant mass flux, saturation temperature (pressure), outlet conditions and fluid properties are investigated. The experimental tests include 172 vaporisation runs carried out at three different saturation temperatures: 10, 15 and 20°C. The refrigerant mass flux ranges from 6.6 to 23.9 kg/m²s and the heat flux from 4.3 to 19.6 kW/m². The heat transfer coefficients show great sensitivity to heat flux, outlet conditions and fluid properties and weak sensitivity to saturation temperature (pressure). 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 refrigerant mass flux. HC-1270 shows heat transfer coefficients 6–12% higher than HC-290 and 35–50% higher than HC-600a and frictional pressure drops 5–10% lower than HC-290 and 2.5 time lower than HC-600a. The experimental heat transfer coefficients are compared with two well-known equations for nucleate boiling and a correlation for frictional pressure drop is proposed.