The process of drying food is extremely complex. Therefore, the mathematical modeling of the process needs high requirements. The combination of approaches in modeling is of practical interest. On the one hand, analytical solutions based on the application of physical laws or phenomenological equations are used. On the other hand, experimental identification of the relationship between temperature and body moisture, which is considered as a peculiar characteristic of heat and mass transfer for each material. It is proposed to consider vacuum microwave drying from the standpoint of physical chemistry as a quasitopochemical heterogeneous reaction and perform mathematical modeling of this process based on the laws of chemical kinetics.

At the present time the maim quantity of free-running food products, including grains, are dried in units with convective method of heat input. To intensify convective drying, general attention is paid to improving the method of moving and mixing the product with drying agent, to guarantee fast and quality drying. The use of high and super-high frequency allows can significantly intensify the drying processes, because the phenomenon of super-high frequencies energy into heat conversion throughout the processed material volume contributes to the most uniform heating of the product, compared to other heat input methods. The optimal solution for drying free-running food products is a combination of convective and high-frequency heat input methods. This combination allows controlling gradients of moisture content and temperature, changing its directions, which significantly affects quality of the resulting dry product. In this regard, combined approach to drying process modeling is of practical interest: on the one hand, there are used analytical solutions, based on physical laws application or phenomenological equations, and, on the other hand, experimentally established a relationship between temperature and moisture content of media, which is considered as a heat and mass transfer characteristic for each material.

At present, there are no reliable criteria for acceptable drying temperatures; so, a new approach is proposed to determine the range of acceptable drying conditions based on a joint solution of the equations that determine the drying kinetics and the kinetics of changes in the process characteristics of the product. For a given product quality, the logarithm of the maximum allowable drying time linearly depends on the reciprocal of the absolute temperature of the drying agent. The method for calculating the drying time is simplified based on a new product characteristic - equivalent moisture content. The criterion of acceptable conditions, which is the maximum temperature of the drying agent, is a function of the magnitude of the thermal effect, the parameters of the drying kinetics, and the kinetics of the process properties of the product.

The main objective of the experimental study of all processes is the analysis, study and generalization of all available results. In accordance with the idea of a step search, the experiment was carried out in several stages. The number of stages and actions at each of them depended on the results of the previous stage and the ultimate goal of research. The ultimate goal of the study is to determine the optimal conditions for the process of mixing the liquid aggregates to obtain a homogeneous structure. Studies of the mixing process were carried out on an experimental setup created at the department. To process experimental studies, the STATISTICA 12 software package was used. To obtain the regression equation, the matrix data were processed using the Microsoft Excel 2010 software package. To optimize the process, the output parameters were converted to a dimensionless scale of desirability d. It was established that the desirability function D, which characterizes the adequacy of the obtained values, has an extremum in experiment 12 and is 0.733666. Based on the obtained data, the following parameters should be considered optimal when mixing liquid aggregates: the peripheral speed of the mixer shaft is within 4 m/s, while the mixing time is 8 s and the refrigerant concentration is 20%.

The article deals with issues related to the study of the connection forms of moisture removed during the drying process of thermolabile heterogeneous products. The difficulties, emerging while developing drying process controlling methods, optimizing energy, material costs, and temperature regimes, necessitate further research. It is shown that the existing methods of studying the forms of moisture connection with the material have significant drawbacks and generally give a qualitative assessment of the state of moisture in the material or are very time-consuming and require long-term laboratory studies. An approach to determining the forms of moisture bond in the material based on graph-analytical analysis of the drying kinetics is proposed, which allows qualitative and quantitative assessment of the state of moisture in the product. With the help of a graphical editor, typical drying kinetics curves were processed and the dependences of the value that characterizes the speed of change in the drying rate on the moisture content of the product were obtained. It is proposed to introduce a new value in the drying theory - drying acceleration. The analysis of the obtained curves testifies to the presence of extremes and inflection points corresponding to the critical moisture content, as well as the presence of areas with slowing or accelerating changes in the drying rate, allowing setting intervals for removing moisture with different binding energy. The approach considered in the article to determining the forms of moisture communication in the material will not only give a qualitative and quantitative assessment of the state of moisture in products, but also reduce the time for analysis and improve the accuracy of the results.