Study of convective and vacuum drying unit operation on the example of apple dehydration

This article presents the results of experimental studies on convective and vacuum drying using apple drying as an example. The schemes of experimental units are shown, and their operating features are described. The kinetics of convective and vacuum methods of apple drying is considered. The study established that the duration of apple drying with the same initial parameters using the vacuum method is almost four times shorter than using the convective method. Several interrelated factors determined vacuum drying period: the total residual pressure in the system; the ratio of partial vapor pressures above the surface of the product being dried and above the evaporator surface; the size and properties of the product (both physicochemical and thermophysical); the method of heat supply to the product being dried; and the maximum permissible product temperature. The experiment has proved that the designed convective and vacuum drying units allow producing dry apples.