Search of Methods for Increasing Absorption Refrigeration Devices Power Efficiency
Authors: A. S. Titlov, I. N. Ishchenko, O. A. Titlova, A. O. Kholodkov, Yu. A. Ocheretyany
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To ensure the safety of food products, many technologies are used. However, no processing technology, except for cooling, is able to extend the shelf life of products and at the same time preserve their original properties. An important role in ensuring the proper quality of food products has a continuous refrigeration chain (CRC). The CRC is a collection of refrigeration equipment and technologies, as well as organizational arrangements that provide the necessary regimes for refrigeration and storage of agricultural raw materials and products along the entire path from producer to consumer. As the long experience shows, the greatest deviation from the recommended and optimal regimes in terms of storage and energy consumption takes place in domestic refrigerators. At present, the most popular refrigerators in the household refrigeration industry are refrigerators based on compression refrigerators. Absorption refrigerators are an alternative to compression refrigerators in domestic refrigeration technology. The composition of the absorption refrigerators includes absorption refrigerating apparatus (ARA), which realize a pump-free absorption-diffusion refrigeration cycle. The working substance of ARA consists of natural components and does not adversely affect the atmosphere of the planet. However, ARA have a significant drawback - more, in comparison with compression analogues, the consumption of electrical energy during operation. Thus, the current task is to reduce the consumption of electricity during the operation of household ARA. The solution of the problem will allow ARA to compete successfully with compression analogues and take a worthy place in the market of household refrigeration equipment. It is shown that significant progress in reducing energy costs during the operation of ARA can be achieved by taking into account changes in the temperature of the outside air, in particular, the air environment of the room. As the analysis shows, the increase in pressure in the system adversely affects the diffusion processes that take place in the evaporator and absorber ARA, since the diffusion coefficient is inversely proportional to the absolute pressure in the system. At the same time, the simultaneous increase in temperature and pressure in the absorber shifts the equilibrium of the water-ammonia solution (WAS) toward large amounts of ammonia in the WAS and, as a result, the intensity of the absorption process increases, despite a certain deterioration in the diffusion processes. The increase in pressure in the system causes a corresponding increase in the temperatures in the generator and the specific energy consumption for evaporation of the WAS. By the positive moment of ARA operation in conditions of high ambient air temperature, it is possible to include minimal losses from the surface of the thermal insulation casing of the ARA generator assembly. The first and the main - the lift section of the reflux condenser works as an ammonia condenser, and the condensate flows into the generator. The second factor is that most of the heat supplied is dissipated into the environment. As a result, a small amount of ammonia enters the condenser and further into the evaporator, which even under favorable operating conditions cannot provide the required cooling conditions in the cooled chambers. To assess the energy efficiency of the operating modes of the ARA generator at various pressure levels in the system, an appropriate analysis was conducted, taking into account the results of ex-perimental studies of serial ARA produced by the Vasilkovsky Refrigeration Plant. The pressure in the system varied from 12 to 20 bar. The analysis of the obtained results allows to draw a conclusion about the favorable effect of the reduction of the pressure level on the energy efficiency of the ARA generator. Thus, with a pressure drop of 20 bar to 12 bar, the specific heat consumption for evaporation of 1 kg of ammonia is reduced by 7.8%. There are proposals to reduce the working pressure in the ARA system associated with changes in the composition of the working fluid, in particular, the amount of inert gas (hydrogen) when the temperature of the surrounding air changes. Their disadvantage is the complexity of the design of the control system and the need for sources of electrical energy. To increase the autonomy of ARA, the external impact on the system is promising. Promising is the possibility of forced blowing of heat dissipating elements (absorber, condenser, dephlegmator) both by using fans with electric drive (when driving a vehicle) and driven by a flow of hot gases (in the parking lot). In view of the cooling effects found, the original design of a transport absorption refrigerator with forced external air cooling the heat dissipating elements of the ARA (absorber and condenser) was proposed, while the temperature potential of the combustion products (220 ... 260 °C) flowing through the ventilation duct was suggested as a circulation stimulator.