Abstract: Basing on the analysis of micro-structure and the experimental data of equilibrium moisture content of the porous construction materials, this paper studies the relationship between the equilibrium moisture content and the void distribution of porous materials.The results show that the void distribution obeys log arithmic normal function.According to this, the relation between the vapor pressure P(r)/P_H and the moisture content of the porous materials in the falling rate drying period is obtained.The calculation result approximately agrees with the experimental data with only 3.01% root mean square error.In addition, the effects of the void distribution parameters μ, σ, the temperature and the moisture content on the vapor pressure P(r)/P_H of the porous materials in the falling rate drying period are analyzed.The results can be used to study the heat and mass transfer of porous materials during the falling rate drying period.

Key words: falling rate drying, porous construction materials, void distribution, the vapor pressure inside the void