Kinetics of heat and moisture exchange and method for calculating the duration of the convective drying process of natural leather

Methods for processing experimental data based on generalized variables of the drying process, which characterize the most general patterns of drying in a period of decreasing speed, are considered. A method for processing experimental data based on the expanded level of drying kinetics is presented, which allows obtaining all dependencies for calculating the main parameters of the drying process. Equations are given for determining the densities of heat fluxes, the intensity of moisture evaporation, the temperature of the material, and the duration of drying for the period of falling speed. A dependence is given for calculating the Rebinder number, which establishes a relationship between moisture exchange and heat exchange for the second drying period. The values of all the coefficients in the equation for the Nusselt heat transfer criterion, which are necessary for determining the heat transfer coefficients, have been established. Calculations of the heat transfer coefficient for a number of modes of natural leather drying are presented. On the basis of the method for calculating the drying kinetics developed by B.S. Sazhin, an equation was established to determine the drying time of leather, which describes the entire drying process, including both drying periods. This method of calculating the kinetics of drying contains a minimum number of coefficients determined empirically, which reduces the amount of work at processing these experiments and the number of necessary experiments. The main constants in the criterial heat transfer equation for determining the heat transfer coefficient have been determined. Verification of the reliability of all obtained equations and comparison of the calculated and experimental values for all parameters of the drying kinetics are given. The obtained results of the study of drying natural leathers make it possible to control the technological process, preventing overdrying of the leather, disturbing the temperature regime, which leads to a reduction in energy costs for drying.

natural leather, convective drying, moisture content, wet thermometer temperature, Rebinder number, Bio criterion, drying time, evaporation rate

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