Simultaneous Heat and Mass Transfer Accompanied by Phase Change in Porous Insulation

This paper analyzes the accumulation and migration of moisture in an insulation material. The problem is modeled as a two-dimensional, transient, multiphase flow in a porous slab. The local volume-averaging technique is used to arrive at a rigorous and fundamental formulation of the heat and mass transfer process in an insulation system. The controlling parameters and assumptions are presented in detail. The equations are solved by devising a two-phase numerical scheme to obtain the condensation regions and the factors which affect the temperature distribution. The phase change process and its effects on the temperature, vapor density, moisture content, liquid content, and the vapor pressure distributions are discussed in detail. The significant transport mechanisms are identified and a simplified formulation of heat and mass transfer, accompanied by phase change, in an insulation system is presented.

An Experimental Investigation of Heat Transfer in Variable Porosity Media

This paper presents an experimental investigation on the effects of a solid impermeable boundary and variable porosity on forced convection in porous media. Emphasis is placed on the channeling effects on heat transfer in packed beds. The local volume-averaging technique is used to establish the governing equations and a numerical scheme is developed which incorporates the boundary and variable porosity effects on heat transfer. The experimental results for the heat flux at the boundary are presented as a function of the pertinent variables in a packed bed. The Nusselt number is found to increase almost linearly with an increase in the Reynolds number based on the pore diameter. The experimental results are found to be in good agreement with the theoretical results which account for the variable porosity effects. A comparison between the numerical and the experimental results demonstrates the importance of boundary and variable porosity effects on heat transfer in variable porosity media.