Abstract
Hratii T.I. Development of combined absorption refrigerating devices
Qualifying scientific work on manuscript rights.
Dissertation for the Doctor of Philosophy degree in specialty 142 "Energy Engineering". Odessa National Technological University, Odesa, 2023.
The dissertation is devoted to the theoretical and experimental research of energy-saving household appliances with extended functionality. Combined absorption refrigerating devices based on absorption refrigerating units were developed and substantiated. Such combined systems make it possible to expand the capabilities of household appliances by combining the functions of cooling and heating in one device without additional energy consumption due to the utilization of the waste heat of dephlegmation of the absorption refrigeration cycle.
The world's leading economies have completed the transition from compressor refrigeration equipment to environmentally friendly and natural refrigerants, but there are still transition problems that force manufacturers to pay attention to absorption domestic refrigeration equipment.
In the market of household refrigerating equipment, absorption models have a minimal cost compared to analogs of the compression type, which most often attracts potential buyers.
At the same time, energy efficiency is an equally important criterion for household refrigeration equipment. According to this parameter, compression models are significantly superior to absorption analogues.
Increasing the energy efficiency of absorption refrigerating devices of various functional purposes is the main direction of modern development of new models.In this trend, the development of new technology is organically recorded, in which expanded functionality is achieved due to the utilization of waste heat of the refrigeration cycle, for example, the cycle of the absorption refrigeration unit (AHA).
Based on the results of the analysis, it was clearly proven that the modes of operation of the AXA dephlegmator determine the energy efficiency when obtaining artificial cold and the thermal modes of the additional TK as part of the combined absorption refrigerating device. Modern mathematical modeling of the thermal modes of the dephlegmator is carried out for its stationary and non-stationary modes of operation, and such known approaches can be used in the modeling of the thermal chain "AXA dephlegmator-two-phase thermosiphon-TC".
An analysis of the current state of development and research was performed, and the task of further research was determined.
The design under study is based on the household absorption refrigerator "Krystal-408" of the Vasylkiv refrigerator factory. The geometric parameters of the TC were: height – 0.420 m; depth – 0.540 m; width – 0.570 m; useful volume – 35 dm3. A two-phase thermosyphon (DFTS) with a length of 1.530 m and a diameter of 0.010×0.001 m was used to ensure the thermal connection of the AXA dephlegmator with the TC. The material of the DFTS body is stainless steel. The coolant is ethyl alcohol. The DFTS was attached to a dephlegmator with a diameter of 0.016×0.0014 m using a copper compression plate, and to reduce thermal resistance, a compressed highly porous copper-based material was placed in the contact zone, the pores of which were filled with heat-conducting paste.In the process of experimental research, it was shown that a combined absorption refrigerating device can be created on the basis of models of the Vasylkiv Refrigerator Factory with minimal technological modifications.
Testing of the thermal regimes of the unloaded TC was performed. It is shown that a temperature of the order of 40 ºС can be reached in the TK with simultaneous provision of regulatory regimes in the cooling chambers.
Daily energy consumption was determined under the conditions of the experiment. It was 6.9% less than in the absorption refrigerating device in the traditional design.
Modeling of the thermal regimes of the combined absorption refrigerating device was performed. It has been proven that: the amount of heat flow removed from the AXA dephlegmator using the DFTS is sufficient only to maintain the temperature in the TC at the level of 50 °C; additional energy costs are required to maintain temperatures of 70 °С and 100 °С in the TC.
A promising design is proposed, in which the heat of dephlegmation is maximally used due to the complete placement of the lifting branch of the dephlegmator in the volume of the TC. A promising design with direct heating of the working environment in the TC due to the creation of a circulation circuit of the working environment is also proposed.
The developed designs were adapted to the technological capabilities of modern power engineering enterprises, in particular "ZONT" LLC, Odesa.
Key words: energy efficiency, thermodynamic analysis, absorption refrigerating equipment, refrigerant, heat, waste heat, thermosyphon, thermal dependencies, heat utilization
