Hydrocarbon Refrigerant Vaporization Inside a Brazed Plate Heat Exchanger

Abstract

This paper presents the experimental heat transfer coefficients and pressure drop measured during HC-600a (isobutane), HC-290 (propane), and HC-1270 (propylene) vaporization inside a brazed plate heat exchanger (BPHE): the effects of heat flux, refrigerant mass flux, saturation temperature (pressure), evaporator outlet condition, and fluid properties are investigated. The experimental tests include 172 vaporization runs carried out at three different saturation temperatures (10, 15, and 20 °C) and four different evaporator outlet conditions (outlet vapor quality around 0.80 and 1.00, outlet vapor super-heating around 5 and 10 °C). The refrigerant mass flux ranges from 6.6 to 23.9 kg m−2 s−1 and the heat flux from 4.3 to 19.6 kW m−2. The heat transfer and pressure drop measurements have been complemented with IR thermography analysis in order to quantify the portion of the heat transfer surface affected by vapor super-heating. The heat transfer coefficients show great sensitivity to heat flux, evaporator outlet condition 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 exhibits 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 60% lower than HC-600a. The experimental heat transfer coefficients are compared with two well-known correlations for nucleate boiling and a linear equation for frictional pressure drop is proposed.