Influence Of Porous Microchannel Configuration On Boiling Heat Transfer And Flow Characteristics

With the development of science and technology,the problem of heat dissipation has been highlighted,and more effective heat dissipation methods are developing.In the aspect of electronic equipment,the heat dissipation problem has become the major problem to be solved,and its local heat flux may reach about 1k W/cm~2.The electronic and electrical equipments require more economic and miniaturized cooling system.This paper focused on the configuration effect of porous microchannel.Three kinds of structure of porous micro channel developed,including regular porous micro channels,flat channel with sintered porous layer and irregular porous micro channel.Some structural parameters,such as the surface contact Angle and porosity,were characterized.The flow boiling heat transfer experiment was conducted using water as the coolant.The visio observation was used to observe the flow patterns of the two-phase flow in the three channels.The test section of the experimental bench was reconstructed.A 5cm-thickness insulation foam was set outside the heat sink chamber to improve the overall thermal insulation capacity of the heat sink chamber and reduce the heat loss during the test.At the same time,the insulation material(PC cover plate bare leakage)was arranged around it.It could ensure that one-dimensional temperature distribution inside the copper column at the upper end of the heating copper block is closer to the one-dimensional heat conduction,so that the calculated value of the wall temperature of the micro-channel is more consistent with the actual value.In the porous channel samples sintered from dendritic copper powder,the capillary liquid feeding ability of samples with different particle sizes and mixed types was tested.The infrared capillary liquid feeding results showed that the liquid feeding ability of samples sintered with 50 micron particle size and with 200 micron bottom thickness was the best,and the corresponding porosity of the sample was also high.At the same heat flux,the pressure drop and pressure pulsation amplitude are lower.It is found that the flow boiling in the porous microchannel can be divided into several stages under different heat fluxes.It consisted of single-phase convection stage(single-phase flow type),subcooled core boiling stage,saturated boiling stage(the plug flow in the channel appears more frequently).and the thin liquid film evaporation stage.From the visualization results,the steam is limited due to the restriction of ribs in the regular micro-channel,compared with the flat channel.The swing phenomenon of the gas-liquid interface is observed in the flat channel.The irregular microchannel can allivate reverse flow effect because of its special structural design.Although the irregular microchannel reduces the heat and mass transfer interface,the boiling heat transfer and flow performance are more outstanding.