Porous Medium Heat Transfer Coupling Analysis And Verification Of The Form

The coupling of heat and mass transfer is the basis of studying and analyzing the heat and mass transfer characteristics of porous materials.The porous materials in the drying process involves heat conduction,heat convection,phase change heat,humidity and other physical distribution transformation phenomenon,these phenomena occur simultaneously which transfer the coupling of heat and mass form abnormal complicatedly,although scholars had put forward many coupling forms and theoretical models,recognition has not yet been unified.Therefore,it is necessary to analyze and verify the existing coupling forms.First of all,based on Hot air drying model in planar,cylindrical and spherical clay(plate thickness equal to cylindrical and spherical diameter)of the same initial boundary value drying condition,get the temperature and humidity change curves of different shapes of clay drying process.Planar,cylindrical and spherical clay to dry the equilibrium time were 2.2h,2h,1.5h;the change trend of temperature and humidity are consistent on the whole;the results show that the different shapes of different clay drying efficiency,the drying efficiency is greater than the spherical clay than cylindrical flat;different shape models with the same coupling form,heat change trend consistent.Secondly,The basic drying in porous media based on the theory of heat transfer,Fick diffusion theory and Fourier theory and Luikov theory and combined with the constant value boundary,adiabatic boundary and coupling the convective boundary of three kinds of boundary conditions are established based on different combinations of the models,in contrast to verify the method is stable and reliable on the basis of the different boundary conditions by using isothermal desorption the wet and heat transfer process of red brick wall,internal temperature and humidity evolution process were calculated.By comparing the results of the numerical analysis,we can obtain:evaporation desorption described Luikov equation optimized effects of changes in temperature gradient and humidity gradient of heat and mass transfer effects or the coupling form of inhibition is the limitation of the process.In the isothermal moisture transfer and heat transfer of wet conditions,temperature and humidity control of the temperature gradient curves show that the mass transfer equation in porous materials influence the moisture diffusion that violate the law of conservation of mass;the Luikov optimization model of the coupling form can exaggerate the effect of latent heat of evaporation inside the material.It is shown that the governing equations for the general drying conditions which can basically reflect the drying characteristics are not applicable to the special conditions such as isothermal heat transfer and wet heat transfer.