Analysis Of Momentum And Heat Transfer At The Porous/free Fluid Interface

The porous composite system,which is composed of the porous region and the adjacent free fluid region,has extensive industrial applications,such as porous aerostatic bearing,transpiration cooling system,drying processes,heat pipe,etc.Therefore,the research of fluid flow and heat transfer inside the porous composite system has significant value in both engineering and academic field.Since the boundary conditions at the interface between the porous medium and the free fluid layer has a great effect on the performances of the porous composite system,this work mainly focuses on the study of the momentum and heat transfer at the porous/free fluid interface.In this work,the impact factors of velocity slip coefficient and the stress jump coefficient,which are the adjustable parameters in the velocity slip and the stress jump boundary conditions respectively,are discussed.And the relative errors of interface velocity,predicted by velocity slip coefficient and the stress jump coefficient,respectively,are also investigated.The cambered brush system is approximately treated as the microscopic model of porous composite system.The conformal mapping method and the two-domain approach are adopted to obtain the microscopic solution and macroscopic solution of velocity profile in the entire system,respectively.Given the limitation of the mapping function,the above work only takes into account the working condition of the large thickness of free fluid layer.The numerical method is used to study the relevant problems of the interface parameters when the thickness of free fluid layer is small.By establishing the microscopic model and macroscopic model of the porous composite system,the impacts of the flow types(including the Poiseuille flow,the Couette flow and the free boundary flow),the free fluid layer thickness,the pore diameter and the porosity on the stress jump coefficient and the interface Biot number in the stress jump and the heat flux jump boundary conditions respectively,the Biot number inside the porous medium and the overall Nusselt number are discussed under the local thermal non-equilibrium condition.A novel method is presented to calculate the interstitial heat transfer coefficient inside the porous medium,when the phenomenon of heat flux bifurcation occurs.The prediction errors of velocity and temperature at the porous/free fluid interface are also analyzed.The analytical solutions of the velocity field,the temperature field,the friction factor,the entropy generation rate and the overall Nusselt number for the channel partially filled with n-layer porous medium are derived,in which the Darcy-Brinkman model and local thermal non-equilibrium model are adopted to describe fluid flow and heat transfer inside the porous medium;The stress jump boundary condition and heat flux jump boundary condition are used at the interface between porous medium and free fluid layer.The stress continuity boundary condition and the heat flux continuity boundary condition are used at the interface between two different porous mediums.Relevant physical fields and relevant performance parameters of the porous composite system with 3-layer porous medium are studied on the basis of the aforementioned analytical solutions.