Auto-cascade Refrigeration System Research Articles

Theoretical performance study on R600/R170 auto-cascade refrigeration cycle with mechanical pre-cooling

A mechanical pre-cooling auto-cascade refrigeration (PACR) system was proposed, R600a single-stage vapor compression system was used to provide pre-cooling for R600/R170 auto-cascade refrigeration (ACR) system. Performance of PACR system under different operating conditions was discussed. The result showed that maintaining a constant outlet temperature of 30°C for the condenser and −45°C for the evaporator in a PACR system resulted in an optimal intermediate temperature that maximized coefficient of cooling performance (COP). At this time, the optimal intermediate temperature of R600/R170 was 0°C, the COP maximum value ( COPmax) was 0.693 and exergy efficiency ( ηEx) was 20.9%. And as the evaporator outlet temperature decreases to −70°C, the optimal intermediate temperature decreases to −10°C. The cooling capacity ( Qe) of the low-temperature grade circulating refrigerant in the PACR system using R600/R170 at different evaporation temperatures was increased by 86.3%–108% compared to that of R134a/R23. COPmax was increased by 7.1% compared to that of R134a/R23 at the evaporator outlet temperature of −60°C.

Effect of mixed refrigerant composition on performance of an auto-cascade refrigeration system using R600a/R1150/R14

Effect of mixed refrigerant composition on performance of an auto-cascade refrigeration system using R600a/R1150/R14

Energy performance assessment of an auto-cascade cycle for ultra-low temperatures with the pair R1150 - R600a

Most of the research about auto-cascade refrigeration systems for ultra-low temperature applications is performed from a theoretical perspective due to the complexity of designing, testing, and measuring systems that work in two-phase conditions in most components of the cycle. A recent developed method has provided the opportunity to understand its thermodynamic peculiarities, which generally differ from the assumptions considered in simulation. This work presents for the first time, a consistent experimental evaluation of an auto-cascade refrigeration system for space temperatures between −80 to −60 °C. The work energetically optimizes a plant with the pair R1150/R600a using three different charging compositions (25/75 %, 30/70 % and 35/65 %) at a heat rejection temperature of 25 °C. Then, for the best option (340 g at 30/70 %), presents the thermodynamic evaluation at three heat rejection levels (25, 30, 35 °C) under steady-state conditions. Experimental measured COP ranged from 0.155 at a heat rejection temperature of 25 °C to 0.087 at 35 °C, with a rated cooling capacity decreasing from 139 W at 25 °C to 87 W at 35 °C.

A novel method to measure the energy efficiency and performance of an auto-cascade refrigeration cycle

Auto-cascade refrigeration systems are the most used cycles to maintain spaces at ultra-low temperature conditions (-80 to −60 °C). The interest in these systems has risen due to the need to maintain and distribute COVID-19 vaccines. However, there is a lack of experimental validation of the theoretical models that are used to analyse and optimize them. In this work, a novel method to calculate the thermodynamic performance, circulating compositions, and energy efficiency of an auto-cascade refrigeration system is presented. The method is based on the measurements of an experimental auto-cascade plant at temperatures from −83.0 to −59.9 °C. The results of the study showed that the proposed calculation method was able to accurately predict the thermodynamic performance, circulating compositions and energy efficiency of an auto-cascade system. The uncertainty of the predictions was found to be below 1% for circulating compositions and 5.2% for the cooling capacity and COP.

Performance evaluation of an auto-cascade refrigeration system using grey correlation theory and response surface methodology

This article focuses on evaluating and analyzing the performance of an autocascade refrigeration system with the zeotropic mixture of R600a/R1150/R14 refrigerants using grey correlation theory and response surface methodology (RSM). The correlation degree among various factors is analyzed using grey correlation theory. The interactive influences that have significant impacts on the six output parameters are illustrated, and a regression model is further validated by five confirmation parameters. The results show that the vapor quality of the evaporator outlet is the greatest factor that affecting the refrigerating capacity and coefficient of performance (COP). However, the evaporation temperature has the greatest effect on compressor’s discharge temperature, pressure ratio, exergy destruction rates, and exergy efficiency. Lower vapor quality of the condenser outlet and condensation temperature can improve the performances of refrigerating capacity, COP, compressor’s discharge temperature, compression ratio, total exergy destruction rate, and exergy efficiency based on the RSM results. The random five groups of validation parameters indicate that the errors between the predicted modeling and calculation results are all less than 5%, demonstrating that the RSM model has good predictability. The results achieved in this work will assist in the optimizing analysis and the application of cryogenic refrigerators.

Theoretical performance comparison for a regenerator-enhanced three-stage auto-cascade refrigeration system using different zeotropic mixed refrigerants

Auto-cascade refrigeration (ACR) systems are widely used at low temperatures. The selection and ratio optimization of zeotropic refrigerants in ACR systems have an important impact on system performance and environmental protection. This study proposes a three-stage regenerator-enhanced auto-cascade refrigeration (RACR) system. Under certain working conditions, the theoretical performances of the three-stage R134a/R23/R14 ACR and RACR systems were compared, and the influence of the refrigerant mixture ratio on the RACR system performance was explored. The system performances of replacing R134a and R23 with different hydrocarbons were compared under different working conditions. The results demonstrated that RACR performed better than ACR alone. A reasonable adjustment to the mixed refrigerant ratio improved the energy efficiency of the RACR system. Water-cooling conditions for the RACR system were suggested, under which the coefficient of performance, thermodynamic perfectness, and exergy efficiency of R600/R170/R14 were 13.8 %, 12.4 %, and 8.4 % higher than those of R600/R23/R14, respectively. The environmental policy, safety requirements, and energy efficiency were considered to obtain −100 °C, R600/R170/R14 with mass fractions of 0.24/0.12/0.64 was the best choice in a water-cooled RACR system.

A novel LNG reproduction layout using ejector refrigeration, an auto-cascade refrigeration system, and an ethylene compression refrigeration cycle

A novel LNG reproduction layout using ejector refrigeration, an auto-cascade refrigeration system, and an ethylene compression refrigeration cycle

Study on the performance of an energy-efficient three-stage auto-cascade refrigeration system enhanced with a pressure regulator

This paper proposed a modified three-stage auto-cascade refrigeration cycle (MTARC) associated with an intermediate pressure regulator. The energy and exergy analyses indicate that the MTARC can acquire lower evaporating temperature, greater cooling capacity and higher COP. Under a typical operating condition, the MTARC using the alternative ternary zeotropic mixture of R1234yf/R41/R14(0.66/0.17/0.17) has an evaporator inlet temperature of −90.90 °C, COP of 0.4509 and exergy efficiency of 40.67%, which are 4.63 °C lower, 32.93% and 15.38% higher than those of the conventional three-stage ARC, respectively. Further research shows that with the decreasing intermediate pressure, the thermodynamic performance of the MARC can be improved significantly, but the compressor exhaust temperature also increases. When the intermediate pressure decreases from 1.8 MPa to 1 MPa, the cooling capacity, COP and exergy efficiency of the MTARC increase by 30.34%, 22.10% and 13.79% respectively, while the exhaust temperature increases 18.59 °C from 116.66 °C to 135.25 °C, which indicates that the selection of intermediate pressure needs to be comprehensively considered. The proposed new approach is valuable for optimizing the design and application of the refrigerator at an ultra-low temperature level of −80 °C.

Theoretical performance comparison for two-stage auto-cascade refrigeration system using hydrocarbon refrigerants

Auto-cascade refrigeration cycle (ARC) is widely used in low-temperature applications. The selection and proportion of refrigerant mixtures in an ARC system have a significant impact on the environment and system performance. In this study, the theoretical performance of a two-stage ARC system using R170/R600a, R170/R600, R1150/R600a, R1150/R600, and R23/R134a was compared. The results showed that, under certain working conditions in the ARC, an optimal refrigerant ratio maximized the COP of the system. At lower evaporator outlet temperatures or higher condenser outlet temperatures, the performance of the system using R170/R600a, R170/R600, R1150/R600a, and R1150/R600 offers advantages over that when using R23/R134a. Among these, R170/R600 afforded the best performance. Exergy analysis was also performed, and the exergy loss ratios of the heat exchanger in the R170/R600 and R23/R134a systems were the highest at 52.3% and 56.7%, respectively.

Energy and exergy performance evaluation of a three-stage auto-cascade refrigeration system using low-GWP alternative refrigerants

l Performance of mixtures consisting R1234yf, R170, R41 and R1132a were investigated within a three-stage ACR. l All alternatives presented promising energy results and can be recommended to replace R23. l The isobaric 3D and the isothermal-isobaric ternary VLE diagrams were presented. l R1234yf/R23/R14 (0.59/0.24/0.17) offers the maximum COP and exergy efficiency of 0.614 and 26.15%. l R1234yf/R41/R14 (0.64/0.17/0.19) is suggested as a promising alternative refrigerant at -100 °C. In order to seek promising refrigerants for vapor compression refrigeration system to obtain ultra-low temperatures down to -100 °C, and to determine whether the low-GWP refrigerants, R41, R170 and R1132a, are suitable substitutes for R23, this study conducted a comprehensive comparative analysis on the cycle characteristics of a three-stage auto-cascade refrigeration (ACR) system using R1234yf/R23/R14, R1234yf/R41/R14, R1234yf/R170/R14 and R1234yf/R1132a/R14. The system performances, including cooling capacity, coefficient of performance (COP), evaporation temperature, compressor discharge temperature, exergy destruction and efficiency were investigated with various compositions and vapor qualities. Results show that R41, R170 and R1132a can all be recommended to replace R23, and the alternatives present promising thermodynamic properties in theoretical simulations. Under the same operation conditions, the cooling capacity of the R1234yf/R41/R14 system is the largest, while the maximum COP and exergy efficiency occur in the R1234yf/R23/R14 system. Considering the energy shortage and environmental pollution issues, R1234yf/R41/R14 with the mass fraction of 0.64/0.17/0.19, COP of 0.2713, and exergy efficiency of 13.91% performs better and hence can be suggested as an alternative refrigerant for the three-stage ACR operating at -100 °C. The largest exergy destruction component occurs in the compressor, followed by the air-cooled condenser and expansion valve, on which future optimization work can be carried out. The results provide a basic theoretical analysis of the selection and replacement of refrigerant in three-stage ACR.

Thermodynamic performance of a modified −150 °C refrigeration system coupled with Linde-Hampson and three-stage auto-cascade using low-GWP refrigerants

This study presents a modified vapor compression refrigeration cycle coupled with a Linde-Hampson refrigeration system and a three-stage auto-cascade refrigeration system (LHR-ACR) using low-GWP mixtures as the refrigerant. A mathematical model based on the energy and exergy methods was developed to evaluate the system performances at varied compositions and vapor qualities, including the cooling capacity, coefficient of performance (COP), evaporation temperature, exergy destruction and efficiency. The pinch point analysis for the heat exchangers was also carried out. The results show that the improvement of the system performance is accompanied by the rise of the evaporation temperature and the compressor discharge temperature. Thus, a multi-objective optimization scheme is the most comprehensive and optimum for the design of an LHR-ACR system. Results further indicate that the LHR-ACR system has a better thermodynamic performance with exergy efficiency of 15.18% and COP of 0.1438 at −150 °C when the R1234yf/R32 composition, R170/R14/R50 composition and vapor quality are 0.54/0.46, 0.52/0.22/0.26 and 0.45, respectively. The component that shows the largest exergy destruction is the cascade condenser-III, followed by the ACR air-cooled condenser and ACR compressor, on which future optimization work can be carried out. The proposed new approach and the results obtained in this paper will be valuable for the optimum design and application of the refrigerator at ultra-low temperature levels.

Experimental Investigation of the Effect of a Recuperative Heat Exchanger and Throttles Opening on a CO2/Isobutane Autocascade Refrigeration System

An experimental evaluation of an autocascade refrigeration (ACR) system was carried out. A zeotropic mixture of isobutane and CO2 was employed as a working fluid in an autocascade refrigeration (ACR) system. An experimental system was designed and built to study the influence of the recuperative heat exchanger (RHX) and openings of the throttle valves on the system performance. The use of RHX facilitated the condensation process and improved the cycle characteristics. The working mass concentration of CO2 was higher, as it was closer to the nominal concentration and the discharge pressure was lower by 19% to even 39% when the RHX was employed in the system. An increase of up to 20% in the coefficient of performance (COP) was observed. Furthermore, the effects of the openings of the throttle valves on the system characteristics were studied. The change in the openings of the expansion valves affected the mass flows and the working mixture composition. The working CO2 mass fraction increased with higher openings of the evaporator throttle. The subcooling degree of liquid CO2-rich refrigerant increased with higher openings of the expansion valve under the phase separator. The results of the present work should be helpful for design and optimization of autocascade systems working with natural and synthetic refrigerants.

Isothermal measurement and modeling of VLE properties for 2,3,3,3-tetrafluoroprop-1-ene + trifluoromethane + tetrafluoromethane ternary system at temperatures from 253.15 K to 273.15 K

Abstract At present, the difficulty in the research of auto cascade refrigeration system lies in the selection of the mixed refrigerant ratio and the design of system process. Accurate thermodynamic data is the key to solve those problems. In this paper, isothermal vapor liquid equilibrium (VLE) behavior was experimentally studied for the strongly-zeotropic ternary mixture 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) + trifluoromethane (R23) + tetrafluoromethane (R14) at 253.15 K, 263.15 K, and 273.15 K. The pressures and the vapor mass fractions were found to be thermodynamically consistent and were satisfactorily correlated with the NRTL-RK model and the MUNIFAC-SRK model. The average absolute relative deviations of pressure (AARD-p), and the average absolute deviations of vapor phase mass fraction (AAD-y1, AAD-y2 and AAD-y3) are less than 0.25%, 0.0032, 0.0048 and 0.0040 for the MUNIFAC-SRK model, respectively, which are better than those of 0.4%, 0.0138, 0.0198 and 0.0049 for the NRTL-RK model. The results of the MUNIFAC-SRK model showed excellent agreement with the experimental values. The isothermal three-dimensional VLE behavior and the isothermal-isobaric ternary VLE diagrams under 1500 kPa were also established using a flash calculation method.

High phase-separation efficiency auto-cascade system working with a blend of carbon dioxide for low-temperature isothermal refrigeration

A high phase-separation efficiency auto-cascade refrigeration (ACR) system working with a zeotropic mixture of CO2 is proposed in this study. The selection of a high boiling-point component is analysed. A novel zeotropic mixture consisting of a high CO2 (R744) mass fraction together with isobutane (R600a) as a carrier fluid is proposed. An experimental setup was designed, built, and verified to study the ability of the ACR to provide isothermal refrigeration at temperatures lower than the R744 triple-point temperature. The setup employs a recuperative heat exchanger (RHX) for the maximum phase-separation efficiency. The effect of the refrigerant mass charge on the ACR operation was examined. The temperature distribution across the internal heat exchangers (IHXs) was studied as well. The results revealed that the system was very sensitive to the refrigerant mass charge. With a low mass charge, the ACR did not operate correctly owing to the pinch points occurring between the hot and cold ends of the IHXs. High mass charge resulted in increased power consumption and a decreased coefficient of performance (COP). Moreover, tests were conducted to examine the ability of the ACR system, working with a binary mixture of R744/R600a, to provide isothermal refrigeration with different evaporator heat loads. The ACR system was compared in terms of the evaporation pressure and mass flow to a cascade system working with trifluoromethane (R23) in the low stage. The ACR system can be a promising alternative to cascade systems working with R23. The mixture of R744/R600a presented a significant decrease in the global warming potential (GWP) compared with R23. Near-isothermal evaporation was possible with this mixture over a range of vapour quality values. The application range of CO2 was extended to temperatures lower than the CO2 triple-point temperature, using isobutane as a solvent for dry ice. The enthalpy–mass fraction diagrams incorporating a solid fraction area were constructed for the graphical representation of the ACR system.

Analyses of an Improved Double-Absorber Absorption Refrigeration System at Low Temperatures

An auto-cascade absorption refrigeration (ACAR) system could achieve a −60°C refrigeration temperature by low-grade heat. For an ACAR system, its performance is mainly affected by energy and mass coupling of the auto-cascade processes. A novel ACAR system with double-absorber was proposed to get higher-efficient refrigeration as low as −60°C in this context, which used R23-R134a-DMF (N, N-Dimethylformamide) as its working fluids. Theoretical calculation and analyses were conducted under different working conditions. From the calculated results, the new system gained a COP value 20% higher than that of an ACAR system with single-absorber under the same generating, condensing, absorbing and refrigerating temperatures. Compositions of a refrigerant mixture showed key influences on energy and mass coupling of the auto-cascade processes, and an optimal composition of the mixed refrigerants was obtained for the new ACAR system. In addition, it was clearly found that absorbing processes of the new system had great effects on energy and mass coupling of the auto-cascade processes. Based on the difference of absorbing characteristics among R23, R134a and DMF, the absorbing processes were intensified under the different absorbing pressures. As a result, an optimal matching pressure was obtained for the new ACAR system. Energy and mass coupling of the auto-cascade processes were further optimized, and the highest COP value was obtained. The theoretical analyses showed that performance of the innovative ACAR system could be superior to that of an ACAR system with single-absorber at a refrigeration temperature from −55°C to −60°C.

Performance of condensing and evaporating characteristics of an auto-refrigerating cascade system

The condensing and evaporating characteristics of an auto-refrigerating cascade cycle employing ternary zeotropic mixture R600a/R23/R14 are studied in this article. When the outlet temperature of c...

Experimental investigation on the concentration distribution behaviors of mixture in an ejector enhanced auto-cascade refrigeration system

In this paper, the concentration distribution behaviors of the mixture R134a/R23 in an ejector enhanced auto-cascade refrigeration cycle (EARC) were experimentally investigated. Relationships between circulating concentration and charged concentration were explored, and the effects of the heat load and ambient temperature on the composition shift characteristics were analyzed. The results indicated that large composition shift occurred at the operation conditions, and the circulating concentration of the low boiling temperature component R23 at the condenser inlet was 25.9–38.1% higher than that in charge due to the differential hold-up of individual refrigerant components in two-phase region. The concentrations of the component in charge and circulation had a linear relationship in EARC, which was similar to those in conventional auto-cascade refrigeration cycle and Joule–Thomson refrigerator, even though these cycles were different in cycle configurations, mixture and operation conditions. R23 showed higher circulation concentration at higher ambient temperature. As the increasing heat load, the circulating concentration of R23 at the condenser inlet first increased and then decreased. In addition, different preferential solubility of individual components in the lubricating oil led to 15.4% richer R23 before the system start-up than that charged. The circulating concentration varied drastically at the early stage of the pull-down process and then tended to be stable over time. The largest shift of the circulation concentration from the charged concentration in the pull-down process reached 32.6%. This work could provide an in-depth understanding of the behaviors of the mixture concentration in the ejector enhanced auto-cascade refrigeration system.

CO₂-R134a용 2단 팽창식 오토 캐스케이드 냉동기의 성능특성 연구

CO₂-R134a용 2단 팽창식 오토 캐스케이드 냉동기의 성능특성 연구

SECOND LAW ANALYSIS OF AUTO CASCADE REFRIGERATION CYCLE USING MIXED HYDROCARBON REFRIGERANT R-600A /R-290/ R170

Experimental and theoretical analysis investigations are achieved on the performance of the three-stage auto cascade refrigeration system. Energy and exergy analysis of auto cascade system is considered using zeotropic mixed hydrocarbon refrigerant R-600a/R-290/R-170 at different mass fractions of (25.5/42.5/32), (24.25/42.75/33), (23/43/34) and (20.5/43.5/36) %. The experimental work was performed on test rig for three stages auto cascade refrigeration system of one ton capacity which is designed and constructed for the present study. The theoretical analysis was carried out using a simulation software PROII based on EES and REFPROP software. The investigated results of the mixed refrigerant R600a/R-290/R170 have showed an enhancement in COP and cycle capacity by about 12.39% and 15% respectively, and the evaporator temperature of the system has approached a relatively lower value of -60.3°Cat mass fraction (23/43/34) compared to the average value of the other mass ratios. The higher values of the exergy efficiency observed for the condenser, evaporator and compressor were 0.92, 0.87 and 0.7 respectively. Comparison of the auto-cascade performance with R-600a/R-290/R-170 at mass fraction (23/43/34) has displayed an enhancement around 45.3 % in the cycle capacity and 39% reduction in the evaporator temperature compared to the mixed refrigerant R-134a/R-410A at mass fraction (70/30). The theoretical results have displayed a reasonable agreement compared to the experimental results with deviations 33%, 22%, and 18% in COP, cycle capacity and overall exergy efficiency respectively.

Hybrid auto-cascade refrigeration system coupled with a heat-driven ejector cooling cycle

The hybrid auto-cascade refrigeration system with an integrated ejector cooling cycle (HACRS) driven by high-grade power and low-grade heat simultaneously is developed in this paper. The working fluid applied in the system is a zeotropic refrigerant mixture of R170/R600a. The heat-driven ejector cooling cycle is employed to the auto-cascade refrigeration cycle to form a novel hybrid auto-cascade refrigeration system coupled with an ejector cycle (HACRS). The ejector is applied to increase the suction pressure of the compressor, and cooling capacity from the ejector cycle is also utilized by the evaporative-condenser and dephlegmator in the HACRS. The system performance is evaluated, based on the mathematical model of the system from the principle of mass and energy conservation. The results indicate that energy consumption of the compressor in HACRS could be reduced by 50% as compared to that in the conventional auto-cascade refrigeration cycle (ACRC). The HACRS can use the heat-driven ejector cycle and the recovery of exhaust waste heat of the compressor to improve its mechanical coefficient of performance (COPme) effectively.