SIMULATION OF THE DRYING PROCESS OF WALNUTS IN A CONVECTION DRYER
Authors: Yaropud Vitali , Shargorodskiy Serhiy , Luts Pavlo , Lavreniuk Petro 
Published: January 2023

Walnuts are valued in the world for the nutritional and medicinal properties of the fruits and the versatile character of their use. In particular, they are widely used in confectionery, oil and fat, flour milling, pharmaceutical, chemical, fodder, paint and other industries. To ensure the safety of the walnut crop, it is necessary to condition them. Moisture requirements for whole walnuts are not higher than 10%. Moisture content of whole nuts after harvesting can reach 35-45%. Therefore, it is necessary to carry out drying to bring them to condition. Drying of whole nuts in Ukraine is usually carried out under natural conditions in covered, ventilated rooms. This is due to the fact that it is physically difficult to significantly speed up the process of drying whole nuts with the help of special equipment. In addition, it is economically inefficient, as it requires significant expenditure on energy carriers. However, if the volume of walnuts is significant, it is difficult to do without special drying equipment. Therefore, some enterprises apply forced drying of whole nuts with the help of various drying chambers in order to prevent their spoilage.
The purpose of the research is to justify the structural and technological scheme of a convective dryer for walnuts and carry out a simulation of the technological process of drying.
Based on the results of the research, the structural and technological scheme of the convective dryer for walnuts, which is made in the form of a mixer with a vertical screw working body with a lower flow of warm air, has been developed and substantiated.
Using the Star CCM+ software package, the technological process of drying was simulated in the developed convective dryer. A visualization of the process of redistribution (mixing) of walnut fruits in the drying chamber under the action of the screw working body and the distribution of air flow speed and temperature in the drying chamber of the convective dryer was obtained. According to the coefficient of variation, it was established that the quality of mixing is the best (δ = 0.92±0.02) and remains at this level after 392 s from the moment of the start of rotation of the screw working body. It was established that there is a temperature gradient in the working area of the dryer: the temperature in the lower part is 58±2 °С, in the upper part - 43±2 °С. Given the rather fast mixing (392 s), such a temperature difference is not critical.
For a more detailed substantiation of the structural and technological parameters of the developed convective walnut dryer, it is necessary to carry out a full-fledged numerical simulation. It is proposed to choose the following research factors: the angle of the cone-shaped grid, the volume of the drying chamber, the diameter, the step and speed of rotation of the screw working body, the speed and temperature of the incoming air flow. The evaluation criteria should be the coefficient of variation of the redistribution of walnut layers, their average temperature, and the lowest air flow rate in the loaded volume of walnuts.