Flow Boiling Heat Transfer Characteristics and Delayed Dry-Out Ability of Non-Azeotropic Mixtures R245fa/R134a in Microchannels

Microchannel flow boiling heat transfer has the advantages of strong heat dissipation capacity, good temperature uniformity, and compact structure. It is an excellent way to thermally manage electronic devices, but when the heat flux exceeds CHF (Critical Heat Flux), the heat transfer performance deteriorates as the working fluid dries out. Non-azeotropic mixtures have the potential to effectively delay or avoid dry-out during the boiling process due to their temperature slide characteristics which causes the mass transfer resistance. To understand the influence of non-azeotropic mixtures on microchannel flow boiling, using the phase-change microchannel heat sink as the research object, the experiments on the flow boiling heat transfer performance of R245fa/R134a mixtures under different working conditions were carried out, and the characteristics of flow boiling heat transfer were obtained under the different working conditions, and comparison was developed with those of pure substance R245fa. The results demonstrated that a small amount of low-boiling-point components in the high-boiling-point working fluid inhibited boiling heat transfer to some extent, and lowered the average heat transfer coefficient under the non-dryout condition slightly lower than that of the pure substance; however, it also effectively delayed the onset of local dry-out and prevented significant deterioration in thermal transfer performance under the lower mass flow rate and higher heat flux, which could enhance the heat sink’s stability.