Research On Enhanced Heat Transfer And Structure Optimization Of Manifold Microchannel Heat Sink Based On Countercurrent Concept

In recent decades,as electronic equipment has undergone miniaturization and integration,the efficiency of electronic devices has been limited.This limitation results in 80%of the electrical power of electronic devices being dissipated as waste heat.Failure to address the problem of excessive temperature generated by electronic components and equipment in a timely and effective manner can lead to a decline in the overall performance of the equipment.As a result,manifold microchannel heat sink has become a popular heat transfer technology that has garnered significant attention.In this paper,numerical simulation is used to explore the flow boiling phenomenon of complex manifold microchannel heat sink,and the idea of combining the concept of countercurrent flow and manifold is proposed,which provides a new way for thermal management of electronic equipment.First,the Mixture multiphase flow model is used to simulate the boiling of subcooled flow in the manifold microchannel heat sink unit structure.Since there is no reconstruction of the gas-liquid interface,the Mixture multiphase flow model saves computational resources more than the VOF model for reconstructing the gas-liquid interface.The effect of microchannel aspect ratio on the subcooled flow boiling heat transfer and pressure drop characteristics of manifold microchannel heat sink is explored.As the aspect ratio of the microchannel increases,both the average and maximum temperatures of the heating surface decrease.However,higher aspect ratios result in a more uneven distribution of temperature.Increasing the aspect ratio also expands the channel cross-sectional area of the manifold microchannel heat sink and lowers the pressure drop.At the same time,the complex situation of subcooled flow boiling in a Z-type manifold microchannel with a local hot spot of 800 W/cm2 is studied.The distribution of mass flow rate,wall temperature and void fraction in the microchannel can be observed.When dealing with subcooled flow boiling in complex manifold microchannel heat sinks,the Mixture multiphase flow model is more appropriate for generating accurate numerical results while utilizing fewer computational resources.Then,the manifold type of the manifold microchannel is studied,and the idea of combining the Z-type manifold structure and the countercurrent concept is proposed.The Ztype manifold structure is used to distribute fluid,and the countercurrent structure is used to reduce the temperature difference on the heat source surface.The numerical simulation of the single-phase flow in a manifold microchannel heat sink with the inlet as the countercurrent zone is carried out using a symmetrical unit structure.The maximum temperature,average temperature and temperature difference of the heating surface of the improved heat sink are lower than those of the traditional Z-type manifold microchannel heat sink.The arrangement of the countercurrent zone reduces the maximum temperature of the heating surface and increases the minimum temperature,which makes the temperature distribution on the heating surface more uniform.For the traditional Z-type manifold microchannel heat sink,the ratio of the maximum mass flux to the minimum mass flux in the microchannel is about 12.83,while for the manifold microchannel whose inlet is the countercurrent area,the value is about 5.82,which means that the improved manifold arrangement can also improve the uniformity of mass flux distribution in the microchannel.The total pressure drop of the manifold microchannel heat sink with the inlet of the countercurrent area is higher than that of the traditional Z-type manifold microchannel heat sink,and the longer flow channel and higher local pressure drop are the main reasons for the larger pressure drop.The thermal resistance performance evaluation coefficient based on the highest temperature is proposed.The modified performance evaluation coefficients are all higher than 1.Finally,the overall structure of the manifold countercurrent microchannel heat sink is optimized,considering the three factors of manifold type,countercurrent structure and flow direction,which affect the single-phase heat transfer and pressure drop characteristics of the manifold microchannel heat sink.The improved manifold countercurrent microchannel heat sink has a lower maximum temperature and an increase of the lowest temperature,mainly due to the fact that the Z-type manifold arrangement is changed to the ZU-type manifold arrangement,and the unidirectional flow is changed to bidirectional flow.In the case of ensuring the same area of the inlet and outlet of the manifold,the flow arrangement of multiple inlets and multiple outlets is adopted and the length of the microchannel in the flow direction is shortened,so that the total pressure drop is reduced.The ZU-type manifold arrangement is superior to the Z-type manifold arrangement in terms of flow distribution,and the countercurrent flow arrangement is helpful to improve the flow distribution of the Z-type manifold.The countercurrent zone,ZU-type manifold and double-direction inlet layout have improved the overall heat transfer performance,and the modified performance evaluation coefficient is higher than that of traditional Z-type manifold microchannels.The bidirectional ZU-type manifold countercurrent flow microchannel heat sink was tested under different heat flux.Under single-phase operating conditions,the heating surface can withstand heat dissipation of 1100 W/cm2 to meet the demand for heat dissipation with high heat flux.