Flow boiling heat transfer of R134a in the multiport minichannel heat exchangers

Abstract

The flow boiling heat transfer characteristics of R134a in the multiport minichannel heat exchangers are presented. The heat exchanger was designed as the counter flow tube-in-tube heat exchanger with refrigerant flowing in the inner tube and hot water in the gap between the outer and inner tubes. Two inner tubes were made from extruded multiport aluminium with the internal hydraulic diameter of 1.1mm for 14 numbers of channels and 1.2mm for eight numbers of channels. The outer surface areas of two inner test sections are 5979mm2 and 6171m2, while the inner surface areas are 13,545mm2 and 8856mm2 for 14 and eight numbers of channels, respectively. The outer tube of heat exchanger was made from circular acrylic tube with an internal hydraulic diameter of 25.4mm. The experiments were performed at the heat fluxes between 15 and 65kW/m2, mass flux of refrigerant between 300 and 800kg/m2s and saturation pressure ranging from 4 to 6bar. For instance the boiling curve, average heat transfer coefficients are discussed. The comparison results of two test sections with different the number of channels are investigated. The results are also compared with nine existing correlations. The new correlation for predicting the heat transfer coefficient was also proposed.