Pore-scale Study On Heat And Mass Transfer Of Evaporating Meniscus Inside Porous Wick

With the rapid development of science and technology,electronic devices gradually tend to be miniaturized and power consumption increases,causing the heat production per unit area increases rapidly.The traditional heat dissipation devices can no longer meet the requirements of electronic devices with high heat flux.Loop heat pipe,as an excellent two-phase heat transfer device,has a good application prospect.As the key component of loop heat pipe,the porous wick provides a liquid working fluid for the two-phase evaporation interface through its capillary pumping force to realize the circulation of the working fluid in loop heat pipe.Studying the characteristics of vapor-liquid phase change interface inside the porous wick has a great significance for understanding the heat transfer inside loop heat pipe and improving its heat transfer performance.According to the three regions of the evaporating meniscus: non-evaporation region,thin liquid film evaporation region and macro-evaporation region,the heat and mass transfer characteristics of the evaporating meniscus are analyzed,and the liquid film length and transfer of each region are analyzed.The heat transfer quantity and the parameters of the meniscus evaporation process are numerically calculated.The thin liquid film area,as the most intense and complicated area of meniscus evaporation,significantly affects the heat and mass transfer of the meniscus in the porous wick.According to the augmented Young-Laplace equation,the influence of the wall and interface pressure difference on the evaporation heat transfer is considered to predict the shape of the evaporation meniscus.Based on the mass conservation and heat transfer equations,a physical model is established,and the evaporation mass flow rate,liquid flow velocity,and evaporation heat load in the thin liquid film region under different working conditions are numerically solved and analyzed by C language.On the basis of numerical calculation,the pore size of the porous wick is processed with normal distribution,and the evaporation heat load of the two-phase interface of the porous wick under this condition is calculated.The evaporation heat transfer of the porous wick is higher when the relative pore size is evenly distributed.Therefore,powder sintered porous wicks have generally better performance than porous wicks with uniform pore size due to their normal distribution of pore diameters,and are more widely used.However,the heat load calculated by the numerical calculation is lower than that under the experimental conditions.The analysis reason is due to the possible extension of the evaporation interface inside the porous wick in the experiment to increase the heat transfer area.Because the evaporation interface may deep into the porous wick,the evaporation area may increase.The interface expansion coefficient is introduced to establish the connection between the microscopic numerical calculation and the macroscopic experiment.