Flow patterns and heat transfer characteristics in flow boiling of R-513A and R-134a refrigerant in open microchannel heat sinks

Abstract

Flow boiling experiments with refrigerants flowing through a multiple microchannel heat exchanger were performed to investigate the resulting flow patterns and heat transfer characteristics. Data were obtained from experiments on saturation flow boiling of R-513A and R-134a flowing through a multiple microchannel heat exchanger with a 655 µm microchannel hydraulic diameter. The test section consisted of 27 microchannels with 300 µm between the top of the fin and a cover plate. Each microchannel was 382 μm wide and 470 μm deep, with a 416 μm fin thickness. The experiments were conducted on refrigerants in horizontal flow at a constant 28°C saturation temperature, with mass fluxes ranging from 200 kg/m²s to 1200 kg/m²s and applied heat fluxes between 10 kW/m²-400 kW/m². Flow visualization was illustrated by using a high-speed camera to observe the flow phenomena and the transition behavior of flow patterns in the microchannels. The results show that the heat transfer coefficient (HTC) of R-513A increases with the heat flux, but decreases with mass flux, while the HTC of R-134a increases with both heat and mass flux. R-134a presents the higher values of HTC in comparison to those of R-513A. Additionally, new correlations were developed and proposed based on these experimental data. The experimental results were also compared to correlations previously reported in the literature.