MASS CONDUCTIVITY IN DRYING CAPILLARY-POROUS COLLOIDAL MATERIAL SUSCEPTIBLE TO SHRINKAGE

The mass transfer (diff usion) properties of a colloidal capillary-porous material (pears cut into plates 5 mm thick for convective drying) as a function of the moisture content of the material at diff erent temperatures of the drying agent (air) were studied experimentally. Since the pear sample shrinks signifi cantly during drying, the change in sample thickness during the process was taken into account when calculating the mass conductivity coeffi cient. At the same time, the linear shrinkage of the specifi ed material was studied. The dependences of the mass conductivity coeffi cient on the moisture content of the material k = f(u) were obtained from drying curves based on the zonal method at a constant temperature of the drying agent tdr. They represent dependences concave to the abscissa axis that increase with moisture content, which is typical of dried materials. The minimum values of the mass conductivity coeffi cient on the graphs k = f(u) vary from 0.3∙10–10 m² /s at 30^o C to 2.2∙10–10 m² /s at 60^o C. With a change in the moisture content of the material, the mass conductivity coeffi cient changes multiply. The shrinkage data for engineering calculations was described by equation. The possibility of describing the temperature dependence of the mass conductivity coeffi cient (moisture diff usion) by Arrhenius equation is shown. The values of the Arrhenius equation parameters are obtained.
The mass transfer (diff usion) properties of a colloidal capillary-porous material (pears cut into plates 5 mm thick for convective drying) as a function of the moisture content of the material at diff erent temperatures of the drying agent (air) were studied experimentally. Since the pear sample shrinks signifi cantly during drying, the change in sample thickness during the process was taken into account when calculating the mass conductivity coeffi cient. At the same time, the linear shrinkage of the specifi ed material was studied. The dependences of the mass conductivity coeffi cient on the moisture content of the material k = f(u) were obtained from drying curves based on the zonal method at a constant temperature of the drying agent tdr. They represent dependences concave to the abscissa axis that increase with moisture content, which is typical of dried materials. The minimum values of the mass conductivity coeffi cient on the graphs k = f(u) vary from 0.3∙10–10 m² /s at 30^o C to 2.2∙10–10 m² /s at 60^o C. With a change in the moisture content of the material, the mass conductivity coeffi cient changes multiply. The shrinkage data for engineering calculations was described by equation. The possibility of describing the temperature dependence of the mass conductivity coeffi cient (moisture diff usion) by Arrhenius equation is shown. The values of the Arrhenius equation parameters are obtained.
Author:  S. P. Rudobashta, V. M. Dmitriev
Keywords:  convective drying, mass conductivity, shrinkage, capillary-porous colloidal material
Page:  1186