Experimental investigation of a novel gas bypass in two-pass microchannel evaporator for performance enhancement

Abstract

The maldistribution of refrigerant flow in two-pass microchannel evaporator will deteriorate heat transfer performance and result in dry evaporating phenomenon. In this article, the experimental method was used to mainly explore the performance of heat transfer and the flow characteristics in the two-pass microchannel evaporator with superheated gas bypass tube installed in the top of middle header, which performance was compared with that of the evaporator without gas bypass. The results showed that the refrigerant gas bypass caused little change on heat transfer and heat transfer coefficient in various testing conditions, but the refrigerant distribution uniformity in the second pass can be significantly enhanced. The two-phase length occurred in the flab tubs increased and the superheat degree obviously decreased when the superheated gas was released through capillary tube. Compared with the microchannel evaporator without gas bypass tube, the maximum increase of the two-phase length in each flat tube can reach 2.2–4 times in different air velocity and refrigerant flow rate. And the maximum decrease of the superheat degree was up to 33 % in the case of 2 m/s air velocity. The results showed that the gas bypass can make the refrigerant distribution more uniform between the flat tubes which will contribute to the reduced superheat degree, use rate of heat exchange area improvement and the relieved dry evaporating in two-pass microchannel evaporator.