The influence of geometric characteristics of the product on the moisture loss kinetics

Abstract

The article is devoted to the influence of the geometric characteristics of the building products surface on the processes of moisture loss during their drying. Drying of a building product is considered as an active physical and chemical process and sensitive to the geometric properties of the moisture transfer flows. The characteristic of these flows is determined, especially, by the boundary conditions, imposed on the humid composite by the sample shape or structure. Due to the fact that the drying of any building product is a complex process, determined by the interrelated changes of the local moisture content, the deformation of the composite and changes at its physical and chemical characteristics, the total effect of the boundary conditions of the moisture sample loss rate of the samples was experimentally investigated. The rate of mass loss due to drying under standard conditions of a series of cubic samples, partly covered with a polymer film is considered in such a way that the areas of the face sections and parts of the surface, containing the edges and vertices free for moisture evaporation remain identical. The moisture loss kinetics was studied using the construction and analysis of the normalized moisture content graph and the corresponding differential graphical dependencies. On the basis of the differential graphs, the intervals of constant speed of moisture loss and reduction of the drying rate were distinguished. It is shown that the interval of constant drying rate in the case of a sample with the isolated edges and vertices is significantly longer compared with a sample with the isolated faces. The speed reduction interval of the drying rate is the smallest in the case of a control sample and the largest in the case of a sample with the isolated edges and vertices. The conceptual interpretation of the obtained results is given: the moisture loss rate both in the case of the constant drying rate mode and in the fall of the drying rate is higher for the samples with the free edges and angles than for the samples with the free faces due to the geometry influence of the sample surface (its curvature) on the evaporation processes and moisture movement through the capillary network of the material. Thus, the significant effect of the geometry surface of the samples, its curvature, the presence of the edges and angles, the nature of moisture loss are demonstrated. The possibility of creating building products with special geometry (the presence of edges and curvature) is considered to optimize the drying processes and minimize the effects of moisture destruction of the material.