Evaporation Heat Transfer and Two-phase Pressure Drop of R32 in a Horizontal Multiport Tube with Triangular Minichannels

Abstract

In this study, an experiment was conducted to investigate the evaporation heat transfer and two-phase pressure drop characteristics of R32 in a horizontal multiport tube with triangular minichannels (Dh = 0.83 mm). The evaporation heat transfer coefficients were measured in a mass velocity range of 50–400 kgm^-2s^-1, heat flux range of 2.5–20 kWm^-2, quality range of 0.05–0.95, and at a saturation temperature of 15 °C. The pressure drop was measured for adiabatic two-phase flow in a mass velocity range of 50–400 kgm^-2s^-1 and quality range of 0.1–0.9 at the same saturation temperature. The heat transfer characteristic was dominated by forced convection evaporation under condition of high mass velocity and high quality. The heat transfer characteristic was dominated by heat transfer at the thin liquid film around a vapor plug in slug flow under low vapor superficial velocity condition. In this study, the effect of nucleate boiling was small, and the heat transfer coefficient decreased with increasing heat flux under low mass velocity condition. The results observed in the horizontal multiport tube with triangular minichannels were compared to those observed in a horizontal multiport tube with circular minichannels. The experiment results clarified the effect of channel geometry on the evaporation heat transfer and pressure drop characteristics.