Refrigeration Technology

The paper is dedicated to the memory of the scientist and teacher, Doctor of Engineering, Professor Valentina S. Kolodyaznaya (1937–2023).

Preservation of quality, nutritional value, reduction of storage losses, increasing the shelf life of raw materials and food products by refrigeration is one of the main tasks of contemporary food technologies.

The article presents a review of long-term researches of Prof. Kolodyaznaya's scientific school on the use of refrigeration technologies to provide food security. The projects supervised by Valentina Kolodyaznaya involved designing of recipes for healthy food products, demonstrated the feasibility of process and storage parameters, created new types of packaging and barrier nanocoatings, allowing to preserve food products for a long time and ensure their high quality and safety. The research papers addressed a pressing national economic problem of reducing losses associated with microbial spoilage of food ingredients, developed freezing and low-temperature storage technologies, proposed biocontrol methods based on the study of microbial communities, and introduced technologies for comprehensive use of all types of both basic and side ingredients.

The paper presents an overview of some studies led by Valentina S. Kolodyaznaya. It is shown that the growth rate of indicator bacteria is much lower during storage of small-piece semi-finished veal products with different coatings, including solutions of organic acids and gelatin and chitosan; sodium alginate and chitosan guar and chitosan in different ratios and in polyethylene packaging.

The paper presents the studies of biofungicides, a set of biocontrol agents used to develop biopreparations reducing the pathogen load on plants during storage at low positive temperatures. Evaluation of antagonistic activity against phytopathogenic microorganisms of fruits and vegetables revealed that some pseudomonad strains (RF13H, RF14J, RM14B, RF12C) have biocontrol and adaptive properties characterised by metabolic and protective activity.

Various methods of freezing plants in air medium, liquid coolants, and vapour nitrogen medium at different temperatures were studied under the supervision of Professor Kolodyaznaya, including studies of partial dehydration by microwave vacuum dehydration and freezing of garden strawberries, blackcurrants, and chokeberries.

Graduates of Kolodyaznaya scientific school continue to work both in research and educational centres and large Russian and foreign industrial companies.

The first paper in this series describes the global history of scroll compressors (SCs), provides a brief analysis of the advantages of SCs over other compressor types, and defines the operating principle of scroll compressors. The paper presents the basic theoretical construction premises for elements of a scroll compressor based on the Archimedean spiral as a generator and reasons for selecting the Archimedean spiral as a generator. It describes some methods for constructing a spiral pen, including a correction method allowing to construct a mathematical algorithm that describes a way to obtain one generator of a spiral pen in the case where the second generator is an Archimedean spiral. This method allows for a high degree of conformity of compressor elements. The following parts of the study describe a theoretical method for obtaining the second generator of the spiral pen using the principles of differential geometry and the envelope curve method. It allowed to obtain equations describing the external generator of the SC element provided that the internal generator is an Archimedean spiral. The paper discusses methods for joining the ends of the scrolls in the central part of the compressor and determines the relative issues. Further, other methods of scroll profiling based on the Archimedeean curve will be presented. In conclusion, there are a brief overview of existing SC modeling methods and a review of relative publications and main areas and trends in this branch of technology.

BACKGROUND: The need for energy conservation is caused by the global social, environmental, and economic agenda. Refrigeration equipment is a significant consumer of power; thus, ensuring energy efficiency of cooling systems for various applications is an urgent task. This area can benefit from regulating the compressor displacement, which in turn is the main energy consumer of refrigeration systems.

AIM: To explain the efficiency of single screw compressor with novel built-in displacement regulator.

MATERIALS AND METHODS: We studied the single screw compressor equipped with a built-in displacement regulator (a rotary adjustment ring). Single screw compressor displacement during its regulation was calculated based on the developed mathematical model automated in the Python programming environment and ANSYS tools. In this case, single screw compressor efficiency was evaluated by two parameters, including volumetric efficiency λ and specific power consumption N_s.

RESULTS: The paper compares the efficiency of single screw compressor for frequency displacement regulation and regulation with a rotary adjustment ring. It was found that regulation with a rotary adjustment ring is preferable.

CONCLUSION: The study revealed the preferable operating range of single screw compressor at the highest values of λ, approximately corresponding to the operation at 1500–3000 rpm. This range can be considered as optimal. Displacement regulation by its reduction using a frequency control outside the selected range will be ineffective. In the regulation range of actual displacement Va ≈ 10%–40%, Ns increases. However, this value in the considered range is lower in regulation with an adjustment ring compared to the frequency regulation (up to 23.7% more effective for air-operated and up to 13.6% more effective for ammonia-operated control ring).