No 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.

The temperature modes of operation of ion-exchange membranes in an electrodialysis apparatus are described. The diffusion permeability of the MK-40 ion-exchange membrane has been experimentally investigated under the conditions of a temperature difference across the membrane at various concentrations of an aqueous solution of sodium chloride. The differences in the diffusion permeability of the membrane in thermostatic and thermodynamic modes are shown. The nature of the influence of the temperature drop across the membrane of aqueous sodium chloride solutions on changes in the value of the diffusion permeability coefficient of the MK-40 membrane was determined.

The paper presents an approach to modeling the surface of a liquid droplet lying on a solid substrate. Receiving the real shape of the droplet surface plays an important role in modeling the process of drying droplets of liquid dispersed systems on solid diffusion-impermeable substrates. This relates to the strong influence of the characteristics of the droplet surface on the values of the coefficients of heat and mass transfer and the value of the surface area of evaporation. A description of the experimental setup for determining the characteristic parameters of the droplet surface is presented. The formulation and solution to the problem of mathematical modeling of the shape of the droplet’s surface, depending on the wetting angle of the liquid-substrate system, surface tension and droplet parameters, are given. The incorrectness of the assumption about the shape of a droplet as an element of a sphere segment is shown. Some results of visualization of the surface of a droplet for various wettability conditions are presented.

The paper presents a description of the modified temperature-moisture relationships, selected on the basis of the analysis of the kinetics of drying of liquid dispersed products on substrates and the methods of engineering calculation of the kinetics of drying with their application. Classification of the types of kinetic curves characterizing the change in the type of thermogram, such as a change in the angle of inclination, deformation and degeneration of the wet-bulb thermometer and boiling plateaux, allows obtaining a modified type of temperature-moisture relationships for their use in calculations of the drying kinetics. The choice of the type of temperature-moisture relationship is carried out on the basis of the solution developed by the authors of the forecast model of the kinetic curve type. The engineering method for calculating the kinetics of drying liquid dispersed products on substrates is based on solving the basic equation of drying kinetics, choosing the type of temperature-moisture relationship, calculating the coordinates of the reference points of temperature-moisture relationship, determined on the basis of the drying mode and the properties of the dried material.