Research Of Heat Transfer In Porous Media And Its Application Basis

Developing basic and applied research of convection and heat transfer in porous media is good for the development building energy-saving new technologies and is the demand of basic science research. The heat transfer law in porous media is studied using theories analysis and experiment study. The influence of fluid Ra number, Darcy number, modal aspect ratio on flow and heat transfer in porous media is studied using numerical calculation method.Firstly, results of experiment study based on theory shows:heat transfer of unsteady state in porous media can be divided into three stages:initial temperature effecting stage, temperature rising stage and new heat balance stage. In the first two stages. top temperature field is affected by the boundary early, bottom temperature field is affected late; the bigger temperature difference is, temperature field is easier to be affected, the shorter the time of initial temperature field effecting. In the third stage, temperature stratification is formed. temperature is high at the top and low at the bottom. That's because natural convection inside fluid appears in porous media.Secondly, Numerical calculation results and experiment results are compared:in new heat balance, the difference of numerical calculation results and experiment results is small, maximum relative error is 10.98%, numerical calculation and parameter setting is verified to be right. The results of study show that:when Ra is small(Ra<105), heat is transferred mainly by conduction, when Ra is increased, convection plays the main part; when Da>10-6, when Da is increased, the easier flow is and the stronger convection is; when aspect ratio is 1, Nu is the largest, heat transfer efficiency is highest. Under linear high temperature condition, when y?0.5, Nu is positive value and decreases with y increasing, heat is transferred from high temperature wall to the cavity; when y>0.5, Nu is negative value and decreases with y increasing, heat is transferred from the cavity to high temperature wall. When the bottom is heated, system stability is broke and bifurcation appears.