Experimental investigation on flow boiling heat transfer characteristics of R141b refrigerant in parallel small channels filled with metal foam

Abstract

This paper reports an experimental investigation of the heat transfer performance of refrigerant R141b during flow boiling heat transfer inside metal foam filled channels. The experiment was conducted at mass flux from 50 to 200 kg/m2 s, heat flux from 4.52 to 13.57 kW/m2 and the cell density of the metal foam is 20 PPI (pores per inch). The flow pattern was visualized by high-speed imaging in the channels. The flow pattern maps were plotted under different heat fluxes, and the underlying reason for the flow pattern transition is the change in vapor quality due to heat absorption. Meanwhile the boiling curves were used for analysis of the relationship between the wall temperature and heat transfer mechanism. The influence of mass flux, heat flux and vapor quality on heat transfer characteristics was analyzed based on heat transfer coefficient. The results show that the flow patterns have a strong impact on the heat transfer coefficient, and simultaneous dry-out phenomenon has a heat transfer deterioration effect. Through the comparison of heat transfer coefficient between empty channels and metal foam filled channels, it is deduced that the heat transfer enhancement of metal foam is about 2.5 to 3 times greater at the mass flux of 100 kg/m2 s and 200 kg/m2 s. A new heat transfer correlation reflecting the heat transfer coefficient change tendency was developed by introducing the Gaussian function, which agrees well with this experimental data. The experimental data of a previous study was used to examine the accuracy of the new correlation; and 90% of experimental data agreed with the predicted values within a deviation of 20%.