Experiments on condensation heat transfer and pressure drop of refrigerant mixtures R245fa/R1234ze(E) inside horizontal microfin tubes.

Abstract

This study experimentally investigated the boiling heat transfer and pressure drop characteristics of R245fa/R1234ze(E) zeotropic refrigerant mixtures inside horizontal microfin tubes. The test tubes were copper tubes with an outer diameter of 9.52 mm, equivalent inner diameters of 8.9 and 8.7 mm, fin heights of 0.12 and 0.18 mm, and fin numbers of 65 and 85, respectively. The experiments were conducted under mass velocities of 100 and 200 kgm–2s–1, mass fractions of 90/10, 80/20, and 65/35 mass% (R245fa/R1234ze(E)), and an average saturation temperature of 40 °C. The measured boiling heat transfer coefficient and frictional pressure drop of the R245fa/R1234ze(E) refrigerant mixture were lower than those of the pure refrigerant R245fa. During the boiling process, the heat transfer coefficient was minimized at a R245fa/R1234ze(E) composition of 65/35 mass%, which had the largest temperature glide. Furthermore, the frictional pressure drops decreased with the mass fraction of R1234ze(E).