New Technical Approaches to Drying Agricultural Foods

Abstract

The use of a refrigeration cycle to raise the temperature has a long history — for the first time such an idea was expressed in 1852 by William Thomson. This article is a theoretical paper devoted to evaluating the possibility of increasing the efficiency of a convective dryer using a heat pump refrigeration unit. The authors of the article present the principle of operation and a constructive calculation of a heat pump refrigeration unit with the construction of its cycle on the Ts diagram for the selected refrigerant (R134a). The analysis of the thermodynamic cycle of the compression heat pump refrigeration unit and the calculation performed for freon R134a show that the selected refrigerant fully provides all operating modes of the convective dryer. The main advantage of the proposed heat pump refrigeration unit for drying is the possibility of returning the latent heat of steam obtained from the moisture of the dried product by reverse condensation of water vapor contained in the spent drying agent (air). A wind turbine can be included in the design of the presented convective dryer, which will generate electrical energy using a generator. For each 1 kW (0.9478 Btu/s) of electricity paid, the user will receive 4.25 kW (4.0282 Btu/s) of free thermal energy. This offers an additional solution for the practical needs of agriculture and the food industry.