Experimental investigation and development of new correlation for flow boiling heat transfer in mini-channel

The flow boiling heat transfer of refrigerant R134a in horizontal multiport mini-channel was experimentally investigated in this paper. Two kinds of mini-channels made of aluminum alloy with the hydraulic diameter of 0.63 mm for 23 rectangular channels and 0.72 mm for 14 rectangular channels were studied. Electric heating film was adopted to provide direct uniform heat flux. The experimental results were obtained with the vapor quality between 0 and 1, the heat flux ranging from 10 to 60 kW/m ², the mass flux ranging from 128 to 560 kg/(m ².s) and the saturation pressure from 0.22 to 0.58 MPa. It was found that nucleate boiling dominates in the low vapor quality region and the heat transfer coefficients of mini-channel are higher than those in conventional channel. The heat transfer coefficients increase with the increasing of both heat flux and saturation pressure but have little dependence with the mass flux. In the high vapor quality region, connective boiling is the main contributor. Heat flux and saturation pressure have little influence on the heat transfer coefficients, but the influence of mass flux is obvious. There is a small increase in heat transfer coefficient with an increase of mass flux. Accordingly, a new correlation for flow boiling heat transfer in mini-channel of R134a was proposed based on Gungor and Winterton correlation. The mean relation deviation is −1.76% and the mean absolute relation deviation is 19.0% respectively. This new correlation is proved to have an obvious accuracy improvement in predicting the flow boiling heat transfer coefficient of R134a in mini-channel. The present work can provide a guidance to the design of mini-channel heat exchanger.