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Heat-using refrigeration machines are created taking into account the characteristics of the external heat sources used; set cooling capacity and cooling temperature; circuit solutions and characteristics of devices. Absorption water-ammonia refrigeration machines (AWRM) allow, in a single-stage design, unlike absorption lithium bromide refrigerating machines, to produce cold at a temperature level up to 243 K. Despite this, their use is constrained by relatively low efficiency. Improving the characteristics of AWRM is an urgent scientific and technical task. Efficiency-enhancing solutions for ammonia-water absorption refrigerating machines can increase their competitiveness with other types of heat recovery chillers. It is proposed to increase the exergy efficiency of AWRM ηe by introducing into their circuit a vapor-compression refrigeration machine (VRM) with a relatively low cooling capacity. For this purpose it is expedient to use VRM for supercooling liquid ammonia as a refrigerant of AWRM. Note that in the vapor-compression refrigeration machine, ammonia is supercooled after the AWRM condenser from Tenv to Tp.c . To determine the energy characteristics of the cooling system under consideration, we will choose a fairly efficient, often used AWRM with a regenerative solution heat exchanger, a rectifier, and a water reflux condenser. Studies of the AWRM+VRM complex have shown that supercooling of liquid ammonia before its throttling contributes to an increase not only in the exergy efficiency ηe, but also in the cooling capacity. For example, in a system that includes an AWRM with a cooling capacity of 500 kW at 258 K and a relatively small VRM, the exergy efficiency and total cooling capacity at pre-cooling to 261 K increase by 11,8% and 18,7%, respectively. The results obtained make it possible to increase interest in such complexes. [ABSTRACT FROM AUTHOR]

Reducing the specific energy consumption of the vapor-compression refrigeration machine by installing an internal heat exchanger-subcooler of condensate, it allows to obtain energy resources savings over a long period of exploitation, аnd at the same time, increases the cost of equipment, so it is important to clarify the calculation of the subcooler and analyze its operation. The work is devoted to the analysis of the existing designs of the subcooler, the choice of criteria for evaluating the effectiveness of the implementation of this heat exchange equipment. Calculated for conditions of numerical experiment theoretical value of the coefficient of thermodynamic efficiency of the cycle.Using the software «Emerson Climate Technologies SELECT 7 (V.7.0)» obtained values of the coefficient of thermodynamic efficiency of the cycle for the subcooler close to the real process taking into account the costs of operation of the compressor. The losses in the compressor to overcome the hydraulic resistance of the heat exchanger-subcooler of condensate were assessed, and the local values of the predicted coefficient of thermodynamic efficiency of vapor-compression refrigeration machine depending on the specific heat capacity of the subcooler were obtained. For the conditions of the numerical experiment, the design of the subcooler was chosen the plate heat exchanger with a smooth surface of the plates, hydrodynamic mode and determining dimensions (gap between the plates).The assumptions and the series of numerical experiments ware performed to calculate the local values of the predicted coefficient of thermodynamic efficiency depending on the length of the channels in the vapor phase.The analysis of the results allowed to determine the optimal length of the heat exchanger, which corresponds to the maximum value of the predicted coefficient of thermodynamic efficiency. Further increase in the length of the heat exchanger leads to an increase in the energy consumption of the compressor to overcome its hydraulic resistance and the predicted efficiency of the machine decreases. The results of the work can be used in the design of new refrigeration equipment, or modernization of existing ones to determine the geometric dimensions and hydrodynamic modes of the heat exchanger-subcooler of condensate. [ABSTRACT FROM AUTHOR]

The increased interest in the hydrocarbon refrigerants application in vapor compression refrigeration systems has been observed last years. But there are absence data both on the phase-separation curve of refrigerant R290 solutions in synthetic compressor oils and on the molar mass of these oils in the literature. This information is necessary for refrigerant/oil solutions thermophysical properties predicting. The results of the study of the average molar mass of ProEco® RF 22S polyester compressor oil and RENISO SP46 alkylbenzene compressor oil, which are recommended for use in refrigerating equipment with R290 are presented in the paper. Methodological problems associated with experimental investigation of the compressor oils molar mass are considered. The measurement of the molar mass was performed by the ebullioscopy method. The description of the experimental setup that implements the ebullioscopy method, also as the experimental technique and the results of the calibration experiments are presented. The obtained data expanded uncertainty does not exceed 5 %. The description of the experimental setup for the investigation of the phase equilibrium parameters for the refrigerant/oil solution is presented. The results of experimental study of the R290 solubility in ProEco® RF 22S and RENISO SP46 compressor oils in the temperature range from minus 58 to 62 °С and a wide range of refrigerant concentrations are presented. It was shown that the R290 refrigerant is fully soluble in ProEco® RF 22S and RENISO SP46 compressor oils in the range of state parameters typical for the refrigerating equipment with the R290 refrigerant. Based on the data obtained, ProEco® RF 22S and RENISO SP46 oils are recommended for use in refrigerating equipment at evaporating temperatures above minus 30 °C. [ABSTRACT FROM AUTHOR]

Pre-cooling was first used in 1900 in an air liquefier. It was demonstrated by K. Linde at an international exhibition. An ammonia refrigeration machine was introduced into the liquefier to cool the air to -50 °C. Later, pre-cooling began to be used in other cryogenic plants. In recent years, there has been growing interest in precooling in chillers. Pre-cooling is advantageously used in combined thermodynamic cycles of cryogenic plants and in systems consisting of two vapor-compression refrigeration machines – VRM. In a system of two VRMs, one of them with a low cooling capacity (VRMII) cools the liquid refrigerant in a larger refrigeration machine (VRMI) before throttling it. The article gives the conclusion of a formula that can be used to assess the possibility of increasing the efficiency of the combined thermodynamic cycles. It is shown how pre-cooling improves the performance of the VRMI + VRMII system. The task of optimizing cooling systems, including two refrigerators, has been posed and solved. The optimal temperatures for pre-cooling of liquid refrigerants R717 and R290 in VRMI were determined, along with which additional VRMII operating on the same refrigerants were used. There is an increase in the cooling capacity Qc and the COP coefficient of efficiency in machine systems of the type R717/R717 and R290/R290. A more significant increase in Qc (by 34%) and COP (by 22.9%) was achieved in a machine of type R290/R600a. The R717 / R600a type car was somewhat inferior to it in terms of performance. It is noted that the maximum COP values are reached in the temperature range of intermediate cooling -5...-10 °С, although in VRMI cold is produced at the level of -30 ° С. The calculation results confirm the feasibility of widespread use of pre-cooling in refrigerators and cryogenic plants. [ABSTRACT FROM AUTHOR]