| With the development of miniaturization and integration technology of electronics,their size is getting smaller and smaller while the power is dramatically increasing.The thermal failure of electronics caused by this has seriously affected the further development.As one of the most efficient thermal management solutions,manifold microchannel heat sink(MMC)are gaining widespread attention.How to further reduce the pressure drop,enhance heat transfer and improve the overall homogeneity of the MMC through structural optimization is becoming the focus of the MMC research.Here,the effects of manifold structure,microchannel structure and porous fins on the flow heat transfer characteristics and comprehensive performance of the MMC are investigated by numerical simulation based on the structural optimization of the MMC,which provides new ideas for the development of the MMC optimization and thermal management technology.Firstly,the MMC models with different manifold structures,including rectangular manifold,multi-step gradient rectangular manifold,tapered manifold,parabolic manifold and elliptical manifold,are proposed by the thinking of manifold shrinkage for Z-type manifold which is relatively easy to fabricate and integrate.The effects of manifold structure variations on the flow and heat transfer characteristics of the MMC are then investigated.The results demonstrate that the manifold structure optimization can significantly reduce the flow resistance in the MMC.The reason for this is that the manifold shrinkage creates along-travel hindrance to the fluid flow in the manifold and forces the fluid momentum to change,thus alleviating the inhomogeneous distribution of fluid among the microchannels which avoids a large accumulation of fluid at the end of the manifold and reduces the local loss of fluid in this region,thus reducing the overall pressure drop.In addition,the uniform distribution of fluid also reduces the overall thermal resistance and temperature difference,enhancing the overall heat transfer.In particular,the parabolic manifold has the best overall performance by reducing the overall pressure drop and thermal resistance by up to 27%and 20%,respectively,and improving the PEC by up to 29.5%compared to the traditional rectangular manifold.The phenomenon of rising and then falling fluid distribution curves caused by elliptical manifold shows that changing the shrinkage of the manifold helps to achieve uniform distributions of fluid and temperature and minimize the overall thermal resistance.This work then investigates the effect of microchannel structure changes on the performance of the MMC,including the traditional straight fin microchannels,staggered fin microchannels,and micro pin-ribs microchannels with different arrangements and diameters,by numerical simulation.The results show that the staggered fins contribute to enhanced fluid perturbation and heat transfer,but also increase the overall flow resistance.The micro pin-ribs microchannels can significantly reduce the overall flow resistance and enhance the heat transfer between the fluid and the micro pin-ribs to improve the overall performance.In particular,the variable diameter staggered micro pin-ribs structure with small gradient can reduce the pumping power and thermal resistance by more than 30%and 21.6%,respectively,and the PEC value increased by 82%～97%,compared with the traditional straight fin MMC,and significantly improve the overall temperature uniformity.The optimization mechanism is to balance the difference in convective heat transfer capacity of fluid at different locations by changing the diameter and number of micro pin-ribs at different locations,achieving uniform temperature distribution and minimizing the overall thermal resistance.Finally,porous fins are introduced into the MMC and the performance of the MMC with the different arrangements of them are investigated.This is mainly attributed to the good permeability of the porous fins allowing the generation of permeate flow inside the fins.When the porous fins are located on the inlet manifold side and the solid fins are located on the outlet manifold side,the fluid is more prone to flow by permeate flow to the area at the end of the inlet manifold,which increases the uneven distribution of the fluid and causes the fluid to flow in a microjet pattern to the outlet manifold,limiting the potential of the porous fins to reduce the pressure drop.When the porous fins are located on the outlet manifold side and the solid fins are located on the inlet manifold side,it increases the space for fluid flow to the outlet and avoids the uneven distribution of fluid.Meanwhile,the presence of permeate flow also enhances the overall heat transfer.Therefore,compared with the traditional solid fin MMC,when the porous fins are located on the outlet manifold side and the proportion of 75%,the pressure drop and thermal resistance are reduced by up to 13%and 19.8%,respectively,and the PEC value is increased by up to 46.2%,which is the best overall performance. |
