On Calculation of Drying Kinetics of Thermolabile Liquid Dispersed Products on Substrates

Abstract

For the drying process of a liquid dispersed product layer on a horizontal substrate, a model for the formation of a solid phase particle residue is proposed. The model is based on the construction of a fractal cluster on a bounded spatial lattice according to given rules. The model is constructed on the basis of ideas about the mechanism of interaction of particles during the existence of a layer of free liquid in the drying product. The fractal model, which has the property of self-similarity of the forming structure, allows modeling spatial structures on bounded lattices and spreading the data obtained on bounded lattices to the entire volume of the simulated residue. The article provides a brief overview of the main works related to the application of the fractal concept in the modeling of micro and macroscopic structures arising during the drying of liquid products. It is shown that in order to calculate the kinetics of drying liquid dispersed products on substrates, in the case of the formation of a certain layer of surface film and the formation of a certain spatial structure of solid particles, an important task is to determine the critical moisture content. The proposed model allows modeling layers with fractal dimension lying in the range from 1.64 to 2. This range corresponds to layers in the porosity range from layers with dense monodisperse particle stacking with a coordination number of 12, to structures similar to dendrite fractals, with porosity much higher than the ordered simple cubic particle stacking. The results of fractal cluster modeling and comparison of calculated and experimental values of porosity and critical moisture content obtained in the process of drying a suspension of optical bleach CD-2 and polymethylene-B-naphthalene sulfonate under different modes of convective drying of the product layer on a fluoroplastic horizontal substrate as products characterized by a close value of the initial concentration of the solid phase (≈12%), but different values of particle sizes and the obtained values of the fractal dimension of the surface film and the dry residue are presented.

Creation of a methodology for determining the intensity of moisture evaporation within vacuum drying of fruits

“…In the following work [15], it is noted that one product dried at different initial concentrations and/or drying modes (soft, hard) forms different kinetic types of curves. Specifically, during the drying of liquid dispersed products in the first period, as a rule, a change in the layer thickness is observed, and in the second period, the evaporation zone deepening inside the formed solid frame is possible.…”

“…According to the principle of non-equilibrium thermodynamics during drying, dry air should diffuse toward the water vapor diffusing from the inner layers of the product to the phase transition surface, which is an insurmountable obstacle for it [15]. Consequently, the concentration of dry air near the surface increases, which, under certain conditions, leads to the appearance of the effect of a convective flow, called the Stefan flow.…”