2016 Volume 33 Issue 3 Article ID: 16-13
This study experimentally investigated the heat transfer and pressure drop characteristics for evaporation and condensation flows of R245fa inside a horizontal smooth tube. The test smooth tube was a copper tube with an inner diameter of 8.32 mm. Evaporation and condensation flows were measured at saturation temperatures ranging from 30– 40 °C and 40–60 °C, respectively, at mass velocities of 50–300 kg/(m2 s). At the same saturation temperature, the differences in the frictional pressure drops of the evaporation and condensation flows were small. Frictional pressure drop increased with increase in mass velocity and vapor quality and decrease in saturation temperature. Similarly, heat transfer coefficients increased with increase in mass velocity and quality and decrease in saturation temperature. The flow patterns inside the tube revealed significant differences in the heat transfer characteristics of evaporation and condensation flows. Further, the experimentally obtained frictional pressure drops and heat transfer coefficients for evaporation and condensation flows were compared with those estimated using correlations reported in the literature. The frictional pressure drops for the evaporation and condensation flows of R245fa and the evaporation heat transfer coefficients were consistent with the previous correlations. Several correlations of condensation heat transfer coefficients tended to be underestimated at low saturation temperatures and high mass velocities in high-quality-region-dominated forced convection. Therefore, a new correlation that considers the gas–liquid density ratio and flow patterns was proposed.
