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This paper presents the application of the multiple-criteria decision-making (SAW) method for selecting the optimum refrigerant for the refrigeration systems of commercial cooling equipment used in gastronomy furniture, which is paramount in storing food under optimal conditions. The analysis focused on comparing different refrigerants, including natural refrigerants such as R744 (carbon dioxide) and R290 (propane) and synthetic refrigerants such as R455A, R449A, and R452A. As a result of the analysis using the SAW method, the refrigerant R455A was found to be the best solution. This choice resulted from the consideration of various decision criteria, such as energy efficiency, environmental impact, operating costs, and technology availability. R455A stands out as a synthetic refrigerant that provides high energy efficiency with minimal environmental impact. Its use supports sustainability goals by reducing greenhouse gas emissions and electricity consumption, which is crucial given the modern regulatory requirements and environmental standards. This study offers a practical decision-making tool for commercial refrigeration equipment designers and manufacturers, supporting them while selecting the optimal technological solutions. The choice of refrigerant R455A addresses the need to integrate energy efficiency, environmental protection, and cost-effectiveness in the process of designing modern refrigeration systems for catering furniture.

The paper identifies and describes the possibilities for heat and mechanical energy recovery within refrigeration systems using CO[sub.2] as a working fluid, employed in commercial and industrial applications. The heat and mechanical energy recovery methods that can be utilized for beneficial purposes are taken into consideration. These methods could increase the energy efficiency of the refrigeration system or the building in which it operates. This paper summarizes various configurations and recovery methods and critically compares and evaluates them (COP improvements, exergy performance, and system integration complexity) based on the data available in the literature. As a result, the internal heat exchangers can be used as a superheater, in which case the COP can increase to 35%. If the internal heat exchanger is used as a subcooler, it could lead to a COP increase of 17% compared to a CO[sub.2] refrigeration system without subcooling for an evaporating temperature of −10 °C and the temperature of the gas cooler outlet of 30 °C. The heat and mechanical energy recovery possibilities are presented using the available scientific literature.

The paper presents a numerical analysis of a tube-in-tube condenser of a small refrigeration system. One of the challenges in designing such units is to reduce their dimensions while maintaining the highest possible cooling capacity, so the research presented here focuses on the search for and impact of the appropriate flow conditions of these two fluids on condenser performance. The refrigerant is supercritical CO[sub.2], which is cooled by water. Thermal-flow simulations were performed for eight CO[sub.2] inlet velocities in the range of 1–8 m/s, and four cooling water velocities of 0.5–2 m/s. The main parameters of the exchanger operation were analyzed: heat transfer coefficient, Nusselt number, overall heat transfer coefficient, and friction factor, which were compared with selected correlations. The results showed that the condenser achieves the highest power for the highest water velocities (2 m/s) and CO[sub.2] (8 m/s), i.e., over 1000 W, which corresponds to a heat flux on the tube surface of approx. 2.6 × 10[sup.5] W/m[sup.2] and a heat transfer coefficient of approx. 4700 W/m[sup.2]K. One of the most important conclusions is the discovery of a significant effect of water velocity on heat transfer from the CO[sub.2] side—an increase in water velocity from 0.5 m/s to 2 m/s results in an increase in the heat transfer coefficient sCO[sub.2] by over 60%, with the same Re number. The implication of this study is to show the possibility of adjusting and selecting condenser parameters over a wide range of capacities, just by changing the fluid velocity.

For many reasons, which will be briefly reviewed in this article, the air cooled packaged chiller is a very popular choice for HVAC designers in capacities up to and slightly above 1,900 kW (550 tons). Until recently, the only compressor types commonly available in air cooled packaged chillers across that entire range were of the positive displacement type. By contrast, for nearly 100 years, the efficiency and other inherent advantages of centrifugal compressors have made them a popular compressor choice in water cooled packaged chillers with capacities as low as 350 kW (100 tons). This article will briefly explore the history of centrifugal compressors when applied in air cooled chiller systems. It will also explain how recent market influences, advances in centrifugal compressor technology, and even new refrigerant choices have coincided to make centrifugal compressors a viable application option for today's HVAC designer choosing to use air cooled packaged chillers.

This paper presents a thermodynamic analysis of a novel dual-ejector transcritical CO.sub.2 refrigeration system for applications in warm climate. Dual-ejector flow-pressurization and flow-splitting for higher ambient temperature operation are implemented to improve the performance. The proposed system is compared with various previously published CO.sub.2 systems including B1 (Standard CO.sub.2 booster system), B2 (CO.sub.2 booster system with parallel compression), B3 (CO.sub.2 booster system with flooded LT evaporator), B4 (CO.sub.2 booster system with work recovery expander), B5 (CO.sub.2 booster system with parallel compression integrated with flooded LT evaporator and work recovery expander) and also with a multi-stage ejector system. The investigation is carried out at ambient temperatures ranging from 34 to 43 °C. Ambient temperature and gas-cooler pressure were found to have a significant effect on the effective flow area of the ejectors. The COP of the proposed system is found to be 32% higher than B5 and 26% higher than the multi-ejector system. Exergy analysis is also carried out to comprehend system response to various parameters including extent of flow-splitting and change in inter-cooler pressure. The ejector Ej-2 was found to have the highest contribution to irreversibility accounting for an increment of 30% with the increase in ambient temperature from 34 to 43 °C. A detailed analysis of the ejector performance is also presented. Mixing chamber diameter is found to be an important parameter affecting the energetic and exergetic performance of the ejector. An enhancement of 29.63% in pressure lift and reduction of 61.11% in the irreversibility contribution of the ejector is possible by increasing the mixing chamber diameter from 0.012 to 0.015 m.

Global warming is one of the most dangerous ecological issues facing the globe. Refrigerants are a major contributor to global warming. This investigation mainly focuses on the analysis of a greener nanorefrigerant. Nanorefrigerant can improve the efficiency of refrigeration and air conditioning systems that use vapor compression. In the present investigation, mathematical and computational methods are used to assess the heat transfer and pressure drop properties of TiO[sub.2]/R1234yf. In order to analyze the heat transfer characteristics and the transport features of the innovative nanorefrigerant, appropriate mathematical predictive models were adapted from earlier investigations. The models are validated by the experiments using TiO[sub.2]/POE nanolubricant as a test fluid. The investigation was conducted with a temperature range of 10 °C to 40 °C and a volume percentage of nano-sized TiO[sub.2] particles in R1234yf refrigerant ranging from 0.2 to 1%. According to the research, the introduction of nanoparticles increases viscosity, thermal conductivity, and density. However, as the amount of nanoparticles rises, the specific heat capacity of the nano-enhanced refrigerant decreases. The nanorefrigerant’s heat transfer coefficient and pressure drop are improved by 134.03% and 80.77%, respectively. The outcomes observed from the predictive technique and the simulation approach had an average absolute variation of 9.91%.

During the last decade, many industrial and medical applications have shown a requirement for low-temperature-cooling usage (from −40 to −80 °C), which cannot be efficiently obtained via the conventional refrigeration systems usually employed for medium-temperature applications (from 0 to −40 °C). A proper ultra-low-temperature (ULT) refrigeration system design is essential to achieve the desired output. The performance can be maximised via the suitable selection of the configuration and refrigerant for a specific temperature range. This work contributes a detailed overview of the different systems and refrigerants used in ultra-low-temperature applications. Different systems, such as single-stage vapour compression, multi-stage, cascade, auto-cascade, and air refrigeration cycles, are presented and discussed. An energy analysis is then carried out for these systems identifying the optimal system design and refrigerant selection to achieve the highest performance. This paper aims to provide the reader with a comprehensive background through an exhaustive review of refrigeration systems suitable for ultra-low-temperature applications. The effectiveness of these systems is proven numerically, mainly based on the temperature level and purpose of the application.

To improve the performance of conventional double-effect absorption refrigeration systems (DEARS), new series parallel (SP) and reverse parallel (RP) configurations using LiCl-H[sub.2]O and LiBr-H[sub.2]O as working fluids, combined with two vapor compressors (VC), are proposed and thermodynamically evaluated. The effects of the distribution ratio (D) and compression ratio (CR) on the system performance are discussed. The results reveal that both configurations can extend the operation ranges of DEARS effectively at a higher distribution ratio, and the performance for low-grade heat source utilization is improved substantially by the use of VC. The compressor positioned between the evaporator and absorber is superior to that between the high-pressure generator and low-pressure generator because of the better performance improvement and larger operating ranges. In all the examined cases, LiCl-H[sub.2]O systems perform better than LiBr-H[sub.2]O systems in terms of the coefficient of performance (COP) and exergetic efficiency. At the higher CR of approximately 2, the compression-assisted DEARS can be driven by heat sources below 100 °C with high levels of COPs above 1.16 for the LiBr-H[sub.2]O working pair and 1.29 for the LiCl-H[sub.2]O working pair. The system can operate at the optimum condition by adjusting the CR values according to the characteristics of the heat sources.