Flow Boiling of Zeotropic Refrigerant Mixture R456a in Microchannels

Zeotropic refrigerant mixtures are widely considered as the alternatives to refrigerants currently used in vapor-compression refrigeration systems for the purpose of lowering GWP. Microchannel heat exchangers prove to be highly efficient and compact. This paper reports local heat flux and local heat-transfer coefficient during flow boiling heat transfer of zeotropic refrigerant mixture R456A in microchannels using an inverse measurement method. The test section is made of two aluminium blocks. Ten parallel horizontal microchannels are machined on the mating surface of the lower block. The channel is 1.0 mm in width, 1.5 mm in height and 440 mm in length. 100 temperature values are measured by 100 thermocouples inserted in holes with 0.6 mm in diameter and 20 mm in depth drilled in the upper and lower blocks, respectively. The local channel surface temperature and local heat flux are obtained by the inverse method using the 100 temperatures measured. The mass flux varied from 200 to 400 kg/m2s, pressure varied from 7 to 9 bar, heating water inlet temperature ranged between 45 and 55°C, and heating water flow rate changed from 310 to 1540 ml/min. The experimental data of flow boiling heat transfer are presented and discussed.