Experimental Study On Subcooled Flow Boiling Of R134a In Rectangle Microchannel Heatsink

Microchannel heat sink cooling system is an effective approach to dissipate high heat flux from electronic chips as a result of its compact structure, high capacity of heat transfer, small temperature difference. Single-phase convective and flow boiling heat transfer are two major ways for heat transfer in microchannels. Flow boiling includes subcooled boiling and saturated boiling.Experiments are conducted to investigate single-phase convective and subcooled boiling heat transfer and flow characteristics of R134 a in microchannel heat sinks. The microchannel heat sinks used in this study consist of 21 microchnnels with hydraulic diameter of 0.75 mm and 0.5mm. The experiment is aimed at investigating the effects of mass flux, saturation, and subcooling degree on heat transfer and fluid flow. The results showed a strong dependence of heat transfer coefficient on mass flux while there are only single-phase convective in microchannels. Heat flux and mass flux both effect subcooled boiling heat transfer and effects of heat flux are much more significant. Microchannel heat sinks performed good temperature-uniformity. When single-phase convective heat transfer turns into subcooled boiling heat transfer, temperature and pressure oscillations were observed in experiments. Correlation were developed to predict heat transfer and pressure drop in microchannels for single-phase forced convective and subcooled boiling. Correlation matched the experimental data within ±25% from the predictions.The mutual influence between microchannel heatsinks connected in parallel or in series are also tested in this experimental. The experimental results indicate that microchannel heatsinks connected in parallel effect each other when pressure drop are different in microchannel heatsinks. Heat transfer mode difference causing pressure drop change finally makes mass flux difference in microchannel heat sinks.This makes performance of microchannel heatsinks connected in parallel differ from single heatsink in stable and dynamic system. Correlation were developed to predict heat transfer and pressure drop in microchannel heatsinks connected in parallel. Correlation matched the experimental data within ±25% from the predictions. Upstream heatsinks of microchannel heatsinks connected in series effect downstream heatsinks by changing temperature and pressure of the working fluid flow into downstream heatsinks. When heat transfer mode in downstream heatsinks changes which makes pressure jump of heatsinks, mass flux changes,Upstream heatsinks temperature changes are also observed in experimental.Results of this study has guiding significance for heat dissipation of multi-heat source and high heat flux electronic chips and provide experimental reference for subcooled boiling heat transfer and flow characteristics in microchannels.