Two-Phase Flow Heat Transfer in Micro-Fin Tubes

Abstract

An experimental investigation of single-phase and two-phase (evaporation and condensation) heat transfer and pressure drop characteristics is performed for five micro-fin tubes with various geometries using refrigerant R22 as the working fluid. The mass flux is in the range of 130–550 kg/m2s. Evaporation tests are conducted at 6 °C saturation temperature, 0.1 inlet quality and 0.9 outlet quality, while condensation tests are carried out at 45 °C saturation temperature, 0.8 inlet quality and 0.1 outlet quality. The results suggest that the micro-fin tubes single-phase heat transfer coefficients increased by 46.3%–63.6% compared to smooth tubes. Tube geometries that have the best evaporation or condensation heat transfer performance are identified. A new evaporation heat transfer correlation that takes the micro-fin effects and heat transfer mechanisms into consideration is developed, which predicts the experimental data within 15% error compared with the previously reported correlations which show prediction errors beyond 30%. The new model is applied to intermittent and annular flow patterns in micro-fin tubes. As for condensation, the Choi et al. correlation well predicts the pressure drop within 20% error, and the Yu and Koyama correlation provides the best heat transfer predictions within 25% error.