Designing and testing a heat pump unit for drying, low-temperature processing, and storing of food products

The use of heat pumps makes it possible to reduce energy consumption in drying processes. This study addresses the problem of efficient use of a heat pump for drying, low-temperature processing, and storage of food products. The object of the study is a heat pump unit capable of operating under the drying mode or under the refrigeration processing and storage mode. Studies have been conducted to design an experimental unit, as well as to improve the energy efficiency of the cooling system. The unit includes a single-stage freon compressor, two air condensers, a water-cooled coil heat exchanger-precondenser, an air evaporator, a thermostatic valve, axial fans, and a unit control system. It has been experimentally established that, depending on the temperature level of condensation of the refrigerant (from +20 °C to +50 °C), the increase in specific cooling capacity with the heat exchanger-precondenser turned off is from 82 kJ/kg to 135 kJ/kg, and with it turned on – from 98 kJ/kg to 143 kJ/kg. In this case, the specific work of compression of refrigerant vapors in the compressor with the heat exchanger-precondenser switched off changes from 36 kJ/kg to 18 kJ/kg. And when it is switched on – from 32 kJ/kg to 10 kJ/kg. That is, the reduction in specific energy consumption is from 4 kJ/kg to 8 kJ/kg, which indicates the advisability of including the precondenser in the installation scheme. In the installation, refrigeration treatment and storage of the product can be carried out in the temperature range from –20 °C to +20 °C and drying – from +10 °C to +40 °C. Under such modes, it is possible to obtain high-quality products with long shelf lives. The results could be used to improve the designs and optimize the operation of heat-transfer drying units and their engineering calculations