Experimental Study on Flow Boiling Heat Transfer of Zeotropic Mixture R290/R601a in a Mini-Channel

The flow boiling heat transfer characteristics of zeotropic mixture R290/R601a in a horizontal mini-channel with an inner diameter of 2 mm were experimentally studied. The experiments were conducted at saturation pressure from 1 to 1.5 MPa, mass flux from 100 to 500 kg/(m2<middle dot>s), heat flux from 20 to 30 kW/m2, and vapor quality from 0 to 1. The effects of mass fraction, mass flux, saturation pressure, heat flux, and vapor quality on the flow boiling heat transfer coefficient in a mini-channel were analyzed. The experimental results show that the boiling heat transfer coefficient initially decreases and then increases with a decrease in the R290 mass fraction. The boiling heat transfer coefficient increases with the increase in mass flux and heat flux and decreases with the increase in saturation pressure. In addition, due to the dry-out phenomenon, the boiling heat transfer coefficient first increases and then decreases with the increase in vapor quality. The experimental data were compared and evaluated with existing correlations. Finally, a new prediction correlation for the boiling heat transfer coefficient is proposed, and the mean absolute relative deviation is 13.7%. This work provides key data for the development of green refrigeration technology, which is helpful in promoting the application of low-GWP natural refrigerants in new refrigeration systems. It also offers experimental guidance for the energy efficiency optimization of the ORC system and the structural design improvement of the compact heat exchanger.