Theoretical basis and practical implementation of “bi-refrigerant” and “two-compressor” refrigeration machine schemes

The operating conditions of the refrigeration machine determine its energy efficiency. Some industries, in particular in the food industry, are characterized by seasonal (short-term) consumption of cold in the low temperature range (-40 ℃ and below), when rapid freezing of the product is required to achieve its high quality due to finely dispersed crystallization of moisture and a shock temperature for psychrophilic microorganisms. Based on this problem, it becomes advisable to periodically use a low-temperature refrigerant, which, from a rational technical point of view, is not always combined with the constant required temperature of refrigerated storage due to possible operation in vacuum conditions and other difficulties. Often the difference between the temperature regime of the required short-term (seasonal or periodic) processing and the constant (main) temperature regime (for example, refrigerated storage of products) reaches 20 ℃ or more, which imposes certain restrictions on the design or operation of the refrigeration machine. In this regard, small and medium-sized refrigeration machines with the ability to operate on two refrigerants (for example, low-temperature and medium-temperature, with periodic automatic mutual replacement) are more promising. Such a refrigeration machine is conventionally called bi-refrigerant in the article. The above difficulties are also solved by the presented scheme of a two-compressor refrigeration machine, in which the possibility of its operation is realized during periodic change of modes from one-stage to two-stage and vice versa, according to the need for the corresponding differences in boiling and condensation pressures