Research Of One-dimensional Coupled Heat And Moisture Transfer In Porous Building

Because our world is confronted with population explosion and threat of energy crisis, all kinds of underground construsction is developing rapidly to save energy and space. Since coefficient of thermal conductivity of soil and building materials is greatly influenced by moisture volume, research on phenomenon of heat and moisture migration should be made to obtain accurate rule of migration of heat and moisture in building envelope and soil so as to accurately determine the energy consumption of underground construsction and ensure its fuction. Accumulation of moisture in construction building evelope could cause deterioration of hear migration performance, degradation of organic material, metal corrosion and damage to building structures etc. In addition, when the ambient moisture is too high, migration of moisture will result in bacteria, then worsen indoor air quality, affect human health. Therefore, the porous media coupled heat and moisture transfer problem has become a hot topic in today's world.This paper based on Luikov coupled heat and moisture transfer equation is put forward to vapor content as driving potential to one-dimensional heat coupling transfer problem, thus solved the actual in moisture content discontinuous problems. Meanwhile, the role of adsorption and desorption in affecting heat and moisture transfer is also considered. In addition, the use of the transfer function method (TFM) for solving coupled heat and moisture transfer in porous media equation has avoided solving the complex eigenvalue. Then the dimensionless temperature and humidity have been introduced, at the same time, the control equation, boundary conditions and initial conditions are dimensionlessed. Then Laplace transforms and transfer function are introduced to transfer the dimensionless coupling of partial differential equations into an ordinary differential equation and then solve to get analytical solutions of the coupled heat and moisture equations. At last, in comparison with experimental results in known literature, it proves that the analytical solution presented in this paper can well predict the complex physical phenomena -the heat and moisture transfer in porous media.In this paper, finite difference method (FDM) is used to discrete equations; and TDMA algorithm is adopted to write appropriate procedures in Fortran environment, coupled heat and moisture transfer problems are numerically solved. The results,compared with the analytical solution, are the further evidence of when the temperature and humidity gradient is not large, the analytical solution is reasonable. This paper numerically solve the coupled heat transfer problem in the two cases of first dry and first wet respectively, and use the experimental results on the literature to verify the numerical solution; Issues for coupled heat in the two cases of isothermal, non-isothermal have been discussed,it finds out the interaction between the temperature and moisture transport. In order to make the study more practical, monolayer wall is extended to the multi-layer wall, the interface coefficient approach is introduced. Numerical simulation has done to multi-layer wall, the requested results are consistent with the experimental well. At the same time, regarding the practical two conditions in summer and winter, namely, the paper analyse temperature and humidity distribution inside the wall simulately, and obtains the temperature, humidity distribution law inside the wall.