Study On The Heat And Mass Transfer Performances Of Microchannel Fluidic System With Boundary Slip At Solid-liquid Interface

With the rapid development of micro/nano manufacturing technology,electronic products tend to be miniaturized,integrated,high-power and multi-function,and orient to high-frequency and high-speed operation mode,which makes the heat production of microelectronic devices is increasing.This further affects the performances and life of electronic components.To solve these problems,seeking and studying new heat dissipation techniques for the cooling of microelectronic devices has become one of the hot issues with high scientific interest.Microchannel liquid cooling system has been widely studied and applied in the field of microelectronic heat dissipation due to its compact structure,convenient use and superior heat dissipation performance.Although in-depth research on the transport mechanisms and optimization design of liquid-cooling heat dissipation technique on the macro scale have been widely carried out,most of the existing researches are based on the classical macroscale theories.The common-used velocity boundary condition at the channel wall of the microchannel is no-slip boundary condition,that is,there is no relative velocity between the solid and liquid at the soild-liquid interface of the microchannel.However,for the fluid flow at the micro/nano scale,no-slip condition is not always applicable,there is another velocity boundary condition named boundary slip existing at some solid-liquid interfaces,and can significantly affect the heat and mass transfer performances of the fluid flow in the microchannel-based fluidic systems.Therefore,it is important to correctly select the velocity boundary condition at the solid-liquid interface of the microchannel and study its influence on the heat and mass transfer performances of the microchannel liquid cooling system.To this end,this present paper investigates the effects of boundary slip on the heat and mass transfer performances of microchannel liquid cooling system using theoretical analysis and numerical analysis.Firstly,based on the theories of fluid mechanics and thermodynamics,this paper established the theoretical models regarding the influences of boundary slip on the fluid resistance and convective heat transfer coefficient of laminar flow in both a single microchannel and tree-like microchannel fluidic system.Then,using the combination of theoretical analysis and numerical simulation,the present paper studied the influences of boundary slip on the fluid resistance and convective heat transfer coefficient of the single microchannel with different cross-sectional sizes and three cross-sectional shapes of elliptical,rectangular and triangular,and then explored the cross-sectional shape and size dependences of heat and mass transfer performances of fluid flow in a single microchannel.Subsequently,the influences of parameters including boundary slip,microchannel cross-sectional size,the branching number,and number of branching level on the heat and mass transfer performances of the tree-like microchannel fluidic system with rectangular and circular channel cross-section shapes are studied.Based on these,the optimal structures of the tree-like microchannel fluid system with optimal heat and mass transfer performances are studied,which provides theoretical guidance for the optimization design of the micro-scale tree-like liquid cooling system.The results in present work show that?1?when there is boundary slip condition at the solid-liquid interface,the fluid resistance of fluid flow in both the single microchannel and tree-like microchannel fluidic systems decreases with the increase of the slip length,while the convective heat transfer coefficient increases with the increase of the slip length.?2?For the tree-like microchannel fluidic system with circular-shaped microchannel cross-section,the optimal structure of the tree-like system with minimized flow resistance satisfies the classical Murray law of?_m=N^-1/3?where?_m is hydraulic diameter ratio of channels at two successive branching level?when the solid-liquid interface has no slip boundary condition.However,when there is boundary slip condition at the solid-liquid interface,the classical Murray law is not applicable.Parameters including slip length,the branching number,the number of branching level,the length ratio of the channels at two successive branching level,etc.can affect the optimal hydraulic diameter ratio of the tree-like microchannel with the minimum flow resistance.?3?For the tree-like microchannel fluidic system with a rectangular cross section,the optimal hydraulic diameter ratio?_m does not satisfy the classical Murray law,?_m decreases with the increasing channel height H,microchannel length ratio?,the branching number N,but increases as the total volume of the microchannels increases.This indicates that direct usage of N^-1/3 as the optimal hydraulic diameter ratio of the rectangular tree-like microchannel fluid system to achieve minimum flow resistance is inaccurate.The research findings in this paper can theoretically develop and improve the relevant mechanisms and theories of the heat and mass transfer performances of microchannel fluidic system,especially the influences of solid-liquid interfacial velocity boundary condition on the heat and mass transfer performances;and can improve the optimization design of microchannel fluid systems and devices,and expand their development and application in the fields of microfluidic transport and heat transfer.