OPTIMIZATION OF R744 CONTENT IN MIXTURES WITH R290, R600, R600A, R170 TO INCREASE THE ENERGY EFFICIENCY OF THE REFRIGERATION SYSTEM

This paper presents a general theoretical analysis of binary refrigerant blends based on R744 (carbon dioxide) in combination with certain hydrocarbons, including R290 (propane), R600 (butane), R600a (isobutane), and R170 (ethane). The main goal of the study was to determine the optimal molar ratios for each of the mixtures that maximize the coefficient of performance (COP), an indicator that characterizes the energy efficiency of the cooling system. In addition, the volumetric cooling capacity (qν) was analyzed, which is an important criterion for assessing the overall efficiency of refrigeration systems. The study analyzed the operation of refrigeration systems, taking into account both subcritical and supercritical conditions. As initial parameters for building a mathematical model, the boiling and condensation/heat removal temperatures were used, which were determined as the average values of the process temperatures in heat exchangers. This approach ensured accurate maintenance of the set temperature in the refrigerating chamber. The best results were obtained for R744/R600 and R744/R600a blends. R744/R600 in the proportion of 58.5/41.5 % has a COP 36.6 % higher than that of pure R600, and the volumetric cooling capacity increased by 10.2 times. Similarly successful results were demonstrated by the R744/R600a blend with an optimal ratio of 93/7 %, which showed a 39.2 % increase in COP and a 16.8-fold increase in volumetric cooling capacity compared to pure R600a. However, the study showed that the use of a R744/R290 blend was less efficient due to relatively lower COP and volumetric cooling capacity compared to pure R744. Similar conclusions were drawn for the R744/R170 blend, which also demonstrated lower efficiency compared to pure R744. At the same time, it is noted that in most component ratios, the mixture operates in a supercritical mode. This indicates that it is inexpedient to use such refrigerant blends at the given initial parameters to improve energy efficiency. This result emphasizes the importance of careful selection of blend components to achieve optimal performance. Overall, the study results demonstrate that the use of R744 blends with R600 and R600a can be a promising alternative to improve the energy efficiency of refrigeration systems. Optimization of the molar fractions can achieve a significant improvement in COP and a significant increase in volumetric cooling capacity, making such blends promising candidates for practical use. However, further development of an in-depth mathematical model that will be close to real operating conditions, as well as experimental studies to verify the actual performance of these blends and identify possible limitations of their use, are required to confirm these conclusions.