Research on heat transfer property of air-air micro channel evaporator

Abstract

Heat exchanger with air-air micro channel is widely used in the refrigeration and air-conditioning industries due to its excellent energy saving and low cost. Recent researches on the air-air micro channel has achieved some available correlations to solve heat transfer coefficient in the channel. However, the available correlations cannot correspond our heat exchanger because the heat transfer for two-phase flow in the micro channel is complex. In this paper, we manufactured an evaporator with the aluminum micro channel heat exchanger and tested its heat transfer efficiency. The heat exchanger, which was filled with R32 as the working fluid, was characterized with the liquid filling ratio $\eta$ ranging from 0.21 to 0.61. We also investigated the thermal performance of the heat exchanger under various temperature differences of the cold and hot air inlets, which ranges from 3°C to 21°C. The experimental results show that the internal boiling heat transfer coefficient increases first and then decreases, with the increasing of liquid filling ratio and the increasing of temperature. On basis of the experimental data, we obtained a new correlation associating with the liquid filling ratio and the temperature difference, which can be used to predict the heat transfer coefficient in the channel. Comparing the predicted value from our correlation with the experimental data, around 88% experimental data falls in the ±15% error bands and the mean absolute error is 7.91%.