Numerical Study Of Heat And Mass Transfer In A Closed Cavity Of Porous Enclosure Structure

Developing research of heat and mass transfer in closed cavity where contains porous enclosure structure has certain theoretical cognition for its behavior of natural convection heat and mass transfer and the basic characteristics,and has great pedagogical implications for indoor temperature control, the creation of the micro-environment and the new technology development of building energy efficiency which include external retaining structure. The problem of mass and heat transfer with porous structure in this complicated cavity is studied by using theoretical analysis and numerical simulation method in this paper.The influence of the porous structure thickness and position, porosity, Ra mumber, Le number, buoyancy ratio and aspect ratio, etc is analyzed by numerical computation, and the streamline, temperature and concentration distribution are concluded.Firstly, theory and numberical calculation are applied to study heat and mass transfer in two-dimensional closed cavity with porous structure. The calculated average Nusselt number Nu compares with benchmark solution, the maximum error is within 0.81%, which to verify the correctness of numerical methods.Secondly, one-domain model is used to study the flow structure and the effect of heat and mass transfer when factors above are different. Conclusions are reached as following:Increasing of the porous structure thickness of the cavity will weaken the effect of heat and mass transfer, and different position of the porous struture has different weakening degree.Regenerative effect is best when the porous structure in the middle of the cavity; With the increasing of porosity, Nu and Sh decrease, so the intensity of convective heat transfer and mass transfer decrease; Effect of temperature on heat and mass transfer is more severer when Le<1, effect of concentration on heat and mass transfer is more severer when Le>1, and effect of the two above is equivalent when Le=1, at this time Nu=Sh; The intensity of flow and heat and mass transfer is weakest when N=-1, the flow is counterclockwise in cavity and the mass buoyancy is dominated when N<-1, the flow is clockwise and thermal buoyancy is dominated when N>-1; Nu and Sh increase as aspect ratio increasing, the effect of heat and mass transfer is more and more obvious; Under linear temperature boundary conditions at the left vertical wall, with the increasing of the thickness of the porous structure, the dominating way of heat transfer in the cavity is from convection to conduction. Heat and mass transfer under different position of local hot wall, Nu and Sh increase first and then decrease, which have maximum when B=0.6. But flow intensity is increased with the increasing of B.Thirdly, this model of complex cavity applies in the heat transfer analysis of a composite wall of contact type porous absorber and arrival at a conclusion:The porous structure plays the effect effective of thermal storage; In contrast materials, the best effect of thermal storage is quartzite. Thermal properties of materials have direct influence on the the effect of thermal storage.