Influence Of Microchannel Structure On Flow Uniformity And Heat Transfer

With the continuous development of integrated circuits,in order to ensure the stable and reliable operation of equipment,it is necessary to ensure that the operating temperature of equipment is within a reliable range.Because of its light weight,small size and high heat transfer efficiency,microchannel heat exchangers can transfer heat with high heat flux to the surrounding medium in time,which has attracted extensive attention of experts and scholars at home and abroad.However,the principle of flow and heat transfer in microchannels differs greatly from that in conventional channels.The effects of the uniformity of flow distribution in microchannels and the roughness of microchannel wall on the flow and heat transfer in microchannels are still hot topics.Therefore,the pressure drop and heat transfer characteristics in microchannels are studied from the fluid flow distribution in microchannels and the wall roughness.The research contents and conclusions are as follows:(1)Two kinds of microchannel heat exchangers,U-type(fluid up-in-out)and Z-type(fluid up-in-out),are designed for the flow in and out of microchannels.By setting up a micro-channel visualization test-bed and using high-speed camera to observe and record the distribution of fluid flow in the micro-channel heat exchanger at different flow rates,the S value of the total fluid distribution non-uniformity in the micro-channel heat exchanger with two different structures is calculated and compared.The results show that the flow rate is different in each sub-channel of the microchannel,and the flow distribution in different pipelines varies greatly.The more Re number of the inlet,the greater the difference of flow distribution in each sub-channel.In the Reynolds number range,the uniformity of Z-type structure decreases by about 70.1%,U-type structure decreases by about 67.3%,and Z-type structure is about 8.7%~22.4% higher than U-type structure.Therefore,under the same Reynolds number,the flow distribution uniformity of micro-channel in Z-type inlet and outlet mode is higher than that in U-type structure.(2)For the problem that the surface roughness of the microchannel has an important influence on the flow heat transfer,a rectangular microchannel with semi-circular roughness element was designed by means of three-dimensional numerical simulation.The effects of rough cells,geometric dimension and Reynolds number on friction coefficient and Nusselt number are studied,and the flow characteristics and heat transfer law of the fluid inside are summarized.The results show that the pressure between the inlet and outlet of the rectangular microchannel decreases gradually with the coarse element spacing in the range of 0.3 mm to 0.5 mm.With the increasing of the spacing between coarse cells,the pressure decreases gradually by approximately 6.85%.The number also gradually decreases,decreasing by approximately 7.02%.In the range of 0.025 mm-0.075 mm,the pressure drop at the inlet and outlet of the rectangular microchannel increases by 10.13% with the increase of the radius of the rough element,and the Nusselt number increases by 8.17% with the decrease of the radius of the rough element.Therefore,the spacing and radius of the roughness are important design parameters of the microchannel.(3)Three kinds of micro-channels with complex structures and smooth micro-channels are studied by numerical simulation method.Through comparative analysis,the flow characteristics and heat transfer law of these micro-channels are summarized.The results show that in the range of Re number studied,the number of Po and Nu of fluids increases with the increase of Re,but the number of Po in microchannel ? is the largest,and that in microchannel ? is the largest.Through analysis,it can be concluded that compared with other microchannels,the performance of microchannel ? is the best.