The objective of research is to develop a low-temperature system and to test a refrigeration unit with a cascade cooling system using a mixture of refrigerants R134a/R23 to provide temperatures down to –70 °C in the cooled volume. The purpose of the low-temperature system is to study the processes of refrigeration treatment and low-temperature storage of food products and materials, enzyme-endocrine raw materials, as well as climatic tests of materials, mechanical devices, and process fluids. Research was conducted at the Scientific and Educational Center Refrigeration, Cryogenic Engineering and Technology of the Federal State Budgetary Educational Institution of Higher Education Kemerovo State University. Based on the design development results, an experimental prototype of the low-temperature system was manufactured, implemented in the form of a chest with a cooled volume of 360 liters. The fundamental, design diagram, and external appearance of the cascade low-temperature system operating on a mixture of refrigerants R134a/R23 are presented. The operability and efficiency of the proposed design of the low-temperature system are proven. The ratio of mass fractions of components in the mixture of refrigerants was selected: 70 % for R134a and 30 % for R23. This ratio ensures the required cooling capacity of the low-temperature system at a refrigerant boiling point in the evaporator of –80 °C, allowing it to reach the specified temperature within a specified time interval of 3 hours at an excess refrigerant discharge pressure of less than 14 atm. The refrigeration unit has been tested. The test results are presented. The low-temperature system reaches a temperature of –70 °C within 3 hours. Moreover, the operating temperatures and pressures ensure stable operation of the unit over an extended period. The presented design solution can be used for low-temperature processing and low-temperature storage of materials at temperatures in the cooled volume down to –70 °C. It is effective for use in biotechnology and pharmaceutical production, as well as for climatic testing of various devices and materials.
Korotkiy et al. (Fri,) studied this question.