Volumetric Refrigeration Capacity Research Articles

Performance analysis of a dual-ejector enhanced two-stage auto-cascade refrigeration cycle for ultra-low temperature refrigeration

Auto-cascade refrigeration cycle (ARC) is a cost-effective solution for ultra-low temperature refrigeration. This paper proposes a dual-ejector enhanced two-stage auto-cascade refrigeration cycle (ETARC). In ETARC, two ejectors replace the throttle valves at the liquid phase outlet of the two gas–liquid separators in the conventional two-stage auto-cascade refrigeration cycle (CTARC). They are connected in series to recover partial expansion work in the throttling process, aiming to lift the suction pressure of the compressor. The ternary mixture component is selected and R600a/R41/R1150 is supposed to be the working fluid due to the best performance. The mass fraction ratio of the refrigerant mixture components, the quality at the inlet of two separators and the expansion ratio of the throttle valve (EPR) of the two cycles are optimized using particle swarm optimization (PSO) with respect to the maximum COP. The performances of the two cycles at optimum operating conditions are compared using energetic and exergetic methods, and the effect of the evaporation temperature and the condensation temperature on cycle performances and operating characteristics are discussed in detail. The results show that applying the two ejectors effectively improves the performance of ETARC. Compared with the CTARC at the evaporation temperature of −85℃, and the condensation temperature of 45℃, the ETARC cycle exhibits 16.07% improvement in COP, 29.43% increase in the volumetric refrigeration capacity qv, 17.17% reduction in the total exergy destruction rate. ETARC shows significant performance improvement and has a remarkable energy-saving potential.

Performance of hydrocarbon refrigerants in a refrigerator with liquid line magnet and CNT nano-lubricant

The issues of flammability associated with A3-class hydrocarbon-based refrigerants are controllable by limiting their mass charges. However, these reductions in their mass charge below certain limits deteriorate their performance efficiency. In this experimental study, we analyzed the effects of a liquid line magnetic field (Mag), multi-wall carbon nanotube (CNT) nano-lubricant, and the combination of both (Mag-Nano) on the performance of a very low mass charge (i.e., 30 g) of R600a and LPG refrigerants, as a replacement to the 100 g R134a refrigerant in a domestic refrigeration system. The refrigerants were tested with and without CNT nano-lubricant (pure), two pairs of 3000 Gs liquid line mounted O ring N50 permanent magnets (Mag), 0.2 g/L concentration of CNT nano-lubricant (Nano), and in combination with a liquid line magnetic field and CNT nano-lubricant (Mag-Nano). The performance evaluation of the refrigerants includes the determination of coefficient of performance (COP), evaporator air temperature, volumetric refrigeration capacity, instantaneous power consumption, cumulative energy consumption, and energy cost. A reduction in the COP of R600a and LPG was observed to be about 11–42% and 14–26%, respectively, when compared to R134a. The R134a refrigerant had the lowest evaporator air temperature of −24.5 °C and the highest instantaneous power consumption of 74.6 W. The R600a-Mag-Nano refrigerant is the most efficient option, having the lowest instantaneous power consumption, energy cost, and cumulative energy consumption. The adoption of hydrocarbon refrigerants is more cost-effective than using the R134a refrigerant, resulting in a cost saving of about 8–26%. In conclusion, the proposed methods adopted to enhance the performance of refrigeration system, are very safe and effective.

Study of refrigeration system with minichannel condenser using R1234ze, R134a, R152a, R600a, R290 and mixture of R290/R600a (50/50)

A versatile vapor compression refrigeration (VCR) system is designed, developed and manufactured for testing different alternative refrigerants to R134a. The refrigerants such as R1234ze, R152a, R600a, R290 and mixture of R290/R600a (50/50) refrigerants are tested with an aluminum minichannel condenser which is designed for R134a. All the refrigerants are experimented for condensation temperature varying from 40 to 55°C while evaporation temperature varying from −10 to +15°C for every condensing temperature. The performance parameters like volumetric refrigerating capacity, actual work consumption of compressor, coefficient of performance (COP) and condenser capacity are compared for different alternative refrigerants. Aluminum minichannel condenser has reduced condensing temperature by 2–3°C with an increase in COP by 10%. The ratio of volumetric refrigerant capacities for R152a, R1234ze, R600a, R290 and HC mixture of R290/R600a (50/50) with respect to R134a are found to be 1.296, 1.143, 0.736, 1.749 and 1.067, respectively which is useful to select specific compressor. The ratio of compressor work for R600a, R290, HC mixture of R290/R600a, R152a and R1234ze with respect to R134a are found to be 1.81, 1.812, 1.867, 1.6 and 1.1, respectively. The ratios of condenser capacity of R600a, R290, HC mixture of R290/R600a, R152a and R1234ze with respect to R134a are found to be 1.914, 2.061, 1.939, 1.65 and 1.064, respectively. It is found that COP of R152a, R600a and R1234ze are larger by 11.53, 5.38 and 27% over R134a whereas COP of R290/R600a (50/50) and R290 are decreased by 0.75% and 14.23% over R134a, respectively. The exergy loss analysis for VCR system components is carried out at condensing temperature of 44°C while evaporating temperature ranging from −10 to +15°C for all the refrigerants and found that total exergy loss is more for R600a among all refrigerants.

Experimental energy evaluation of R516A and R513A as replacement of R134a in refrigeration and air conditioning modes

This paper presents the experimental energy behavior of R516A and R513A compared to R134a as baseline refrigerant in refrigeration and air conditioning temperatures. The comparative is made in an evaporating temperatures range of 261 K to 285 K with step 4 K increases, taking condensing temperatures of 308 K, 313 K, and 318 K. Results show that the best energy performance was reached by R134a while the worst were for R513A in all experimental tests, here R516A shows the smallest difference respect to R134a being just 5.4%. Also, R134a showed lower values in discharge pressure respect to its replacements, while R516A exhibited the lower discharge temperatures. R513A showed lower useful superheating for refrigeration applications, while R516A achieved the minor useful superheating for air conditioning temperatures only below R134a. Finally, R513A reached the higher value of volumetric refrigeration capacity for air conditioning temperatures at 308 K condensing temperature. All results were obtained considering the optimal refrigerant mass charge which were 682 g, 655 g, and 632 g for R134a, R513A and R516A, respectively.

Density and isochoric heat capacity of {x trans-1,3,3,3-Tetrafluoropropene + (1-x) Propane} at temperatures from (285.45 to 349.71) K and pressures up to 10.384 MPa

The increasingly serious global warming problem has accelerated the elimination of traditional hydrofluorocarbon (HFC) refrigerants. R1234ze(E) + R290 binary mixture as a potential alternative refrigerant are expected to overcome the deficiencies of R1234ze(E) (low volumetric refrigeration capacity) and R290 (flammability and explosiveness). In this paper, the 38 density and 119 isochoric specific heat capacity data of R1234ze(E)+R290 mixtures were measured at temperatures from (285.45 to 349.71) K using an adiabatic batch calorimeter with intermittent heating. Uncertainties of temperature, pressure, density and isochoric heat capacity were estimated to be less than 12 mK, 5 kPa, 0.30% and 1.0%. The density data were correlated using the Tait equation, and good regression results were obtained, with the AARD of 0.19% and MARD of 0.83%. A comparison was conducted between the Tait equation and REFPROP 10 and Peng-Robinson equation of state (PR EoS), the Tait equation gives the best prediction performance. In addition, the isochoric specific heat capacity data were compared with the values calculated by four models (PR model, Zhong model, Sheng model and REFPROP 10). Among them, the three models, the Zhong model, Sheng model and REFPROP 10, give the same prediction performance, with AARD of 2.88%, 2.47% and 2.51%, respectively. But for the PR model, the density data has a significant impact on the result, especially for the low-temperature region. When the density data were calculated by the Tait equation, the PR model presents the best prediction performance for the heat capacity of R1234ze(E) + R290 mixtures with the AARD of 2.00%, nevertheless, when the density data were calculated from the PR EoS, the PR model showed a large deviation in the prediction of isochoric heat capacity with the AARD and MARD of 3.74% and 11.11%. An empirical equation was correlated to represent the experimental heat capacity data with the MARD of 3.07% and the AARD of 1.15%.

Thermodynamic performance evaluation of an ejector-enhanced transcritical CO2 parallel compression refrigeration cycle

A parallel compression cycle is one efficient approach to improving the transcritical CO2 refrigeration cycle performance. This paper proposes a modified parallel compression transcritical CO2 refrigeration cycle with an ejector and a sub-cooler to further enhance the cycle performance. The thermodynamic analyses based on the energetic and exergetic analyses are conducted, and the influences of the parameters, including discharge pressure, flash pressure, gas cooler outlet temperature, and evaporation temperature, are discussed. The particle swarm optimization method is used to get the optimal discharge pressure and flash pressure and the temperature reduction in the sub-cooler with respect to the maximum COP. The performance comparisons between the conventional cycle and the modified cycle are presented. The results illustrate that the maximum improvements in COP and volumetric refrigeration capacity reach 15.8% and 17.1%. The utilization of the ejector and sub-cooler could reduce the optimal flash pressure by 16.4–33.0% and the compressor displacement by 11.4% compared with the conventional cycle. The ejector plays a dominant role in performance improvement at a high gas cooler outlet temperature. The exergy destruction analysis shows that the first-largest system exergy destruction ratio of 31.5% in the ejector-enhanced cycle is caused by the gas cooler, and its second-largest exergy destruction is generated in the two parallel compressors instead of the expansion valves in the conventional cycle.

Performance analysis of a modified ejector-enhanced auto-cascade refrigeration cycle

In this paper, a modified ejector-enhanced auto-cascade refrigeration cycle with R290/R170 is proposed on the basis of a basic ejector-enhanced auto-cascade refrigeration cycle proposed previously. An additional expansion valve and internal heat exchanger are utilized in the modified cycle and are located after condenser. Refrigerant leaves condenser with smaller quality and then is throttling in expansion valve. Thus, the quality at inlet of separator can be adjusted to meet varying refrigeration capacity as varying ambient temperature. The thermodynamic analyses based on energy and exergy methods are conducted to compare the performances of two cycles. The influences of several critical operating parameters on cycle performances are investigated in detail. The results indicate that the modified cycle can obtain higher COP under the given operating conditions than the basic cycle. The modified cycle presents average improvement of 7.52%–8.86% in COP and 9.28%–11.33% improvement in volumetric refrigeration capacity. Besides, the exergy destruction of condenser, ejector and expansion valves in modified cycle is much less than that in basic cycle. The total exergy destruction of the modified cycle is decreased by 6.65%–8.35%, and exergy efficiency is increased by 7.54%–8.85%. Therefore, the modified cycle shows its energy-saving advantage and application potential in low-temperature refrigeration.

Vapor-liquid equilibrium measurements and models for the ternary mixtures of R1234yf + R32 + R125 and R1234yf + R32 + CO2

R1234yf as the environmental friendly refrigerant has a low volumetric refrigeration capacity and light flammability. The refrigerant mixtures are expected to achieve excellent thermophysical performance, safety and environmental performance. The vapor-liquid equilibrium (VLE) is one of the most important properties of the mixtures. In this work, the VLE property of R1234yf + R32 + R125 and R1234yf + R32 + CO2 ternary mixtures were measured along 5 isotherms from 273.15 K to 313.15 K by a recirculation analytical apparatus. The Peng-Robinson (PR) equation of state combined with the van der Waals (vdW) mixing rule (PR + vdW), as well as the PR equation of state combined with the Wong-Sandler (WS) mixing rule and the non-random two-liquid (NRTL) activity coefficient model (PR + WS + NRTL) were used to correlate the VLE data. The model parameters were temperature-dependent and could describe the VLE properties of the ternary and binary subsystems. The results showed that the PR + WS + NRTL model was better than the PR + vdW model. The average absolute relative deviation of pressure (AARD(p)) and average absolute deviation of compositions (AAD(y)) of the PR + WS + NRTL model were 0.4% and 0.003 for R1234yf + R32 + R125 ternary mixture, and were 0.7% and 0.007 for R1234yf + R32 + CO2 ternary mixture. Experimental results and model calculations showed that both the ternary mixtures were zeotropic.

Theoretical investigation and comparative analysis of the Linde–Hampson refrigeration system using eco-friendly zeotropic refrigerants based on R744/R1234ze(Z) for freezing process applications

The theoretical simulation and thermodynamic analyses of the Linde–Hampson refrigeration system using multiple eco-friendly zeotropic refrigerants are conducted to compare the optimal COP, volumetric refrigerating capacity and irreversibility distribution at the cold space temperature of -45 °C to -25 °C. The genetic algorithm is employed on the global optimization of Linde–Hampson refrigeration system to find out the optimal operating pressures and proportions of mixed refrigerants. By comparison, the most potential binary and ternary refrigerants are selected as R744/R1234ze(Z) and R744/R1234ze(E)/R1234ze(Z), respectively. The temperature glide of ternary refrigerant is mainly regulated by the proportions of the middle-boiling-point and high-boiling-point components. The temperature glide of zeotropic refrigerants should well match the temperature span between heat reservoirs, since the matching degree plays an essential role in system performance, and it can be regarded as an important basis for the selection of mixed refrigerants. The results of comparison with the R744 two-stage compression transcritical refrigeration system and the cascade refrigeration system using R744 and R1234yf show that the Linde–Hampson system using suitable mixed refrigerants can obtain the greatest COP and can be considered as a supplement and alternative. The research results will provide a reference to the applications of the Linde–Hampson refrigeration system using eco-friendly zeotropic refrigerants for freezing process in considerations of environmental protection, safety, and efficiency.

Thermodynamic performance optimization and analysis of an auto-cascade refrigeration cycle with vapor injection for ultra-low temperature freezer

To improve the performance of the conventional auto-cascade refrigeration cycle, a modified auto-cascade refrigeration cycle with vapor injection is proposed for the application of a -80 ℃ freezer in this study. The particle swarm optimization algorithm is used to obtain the cycle performance at different operation conditions. The mixture concentration, compression ratio and condenser outlet quality are optimized globally. The binary mixture selection is carried out among the R1150/R290, R150/R600 and R1150/R600a. The results indicate that R1150/R600 is proposed as the alternative refrigerant. The performance comparisons between conventional and vapor injection auto-cascade refrigeration cycles show that the vapor injection technique efficiently improves system performance, especially at high condensation and low evaporation temperatures. Compared with the conventional auto-cascade refrigeration cycle, the optimal COP in the modified auto-cascade refrigeration cycles show a 9.3∼53.8% improvement in COP and the maximum improvement in the volumetric refrigeration capacity reaches 58.2% at low evaporation temperature. The statistical results of the optimal concentration of the mixture R1150/R600 at the selected operating conditions show that 88% of the optimal R600 concentration in the VARC cycle is in the range of 0.657∼0.699. The optimal concentration of R600 in the CARC cycle varies in a wide range of 0.57∼0.75. The optimal intermediate pressure is 38.1∼13.4% lower than the geometric mean of discharge pressure and evaporation pressure. The exergetic analyses illustrate that the largest exergy destruction of the VARC cycle occurs in the recuperator-2 instead of the compressor in CARC, contributing to 22.6∼23.5% of the total exergy destruction.

Experimental study of R290 replacement R134a in cold storage air conditioning system

R290 refrigerant offers good environmental protection and thermodynamic characteristics. The feasibility of R290 replacing R134a was summarized through theoretical analysis and experimental tests in this paper. A coiled ice storage experimental test platform was built, and the performance of R290 and R134a cool storage air conditioning systems was analyzed. The experimental analysis confirmed that the R290 system has a higher volumetric refrigerating capacity, and the system COP (coefficient of performance) is comparable to the R134a system. At the same evaporation temperature, the pressure ratio and exhaust temperature of the R290 system are lower than those of the R134a system. In addition, the charge amount of the refrigerant can have an impact on cold storage performance. It was found that the optimal charge range of R134a is 1300–1400 g, and that of R290 ranges from 500 to 600 g. The optimal charge amount for R290 is only 43–46% of R134a. A lower charge amount is beneficial to reduce the explosion risk of the R290 cool storage air conditioner. Under the optimal charge, the R290 system has a fast cooling rate and shorter cooling storage time, and the average specific refrigerating effect is increased by approximately 52% compared with R134a.

Vapor-liquid equilibrium measurements for the binary mixtures of pentafluoroethane (R125) with 2,3,3,3-Tetrafluoroprop-1-ene (R1234yf) and 3,3,3-Trifluoropropene (R1243zf)

R1234yf and R1243zf have received extensive attention as environmentally refrigerants. However, the application of the pure R1234yf and R1243zf are limited due to their flammability and low volumetric refrigerating capacity. The mixed refrigerants are expected to achieve excellent thermophysical performance, safety, and environmental protection. Vapor-liquid equilibrium (VLE) is an extremely important thermophysical property of mixtures. By using a recirculation-analytical type VLE apparatus, the VLE data of the (R125 + R1234yf) and (R125 + R1243zf) binary systems were measured along six isotherms from 263.15 K to 313.15 K. The PR + vdW model is used to correlate the VLE data. The overall average relative deviation of pressure (ARD(p)) and the average absolute deviation of vapor phase mole fraction (AAD(y)) are 0.15% and 0.0011 for R125 + R1234yf system; and the ARD(p) and AAD(y) are 0.16% and 0.0011 for R125 + R1243zf system. The model has a good description of the two binary systems.

NRM30 as a possible substitute for R22 in marine vapour compression refrigeration systems

The purpose of this paper is to investigate the possibility of using NRM30 in order to replace R22, in existing plants on board the ships. NRM30 is a refrigerant mixture of R134a/R1270/RE170 (55/37.5/7.5 by mass percentage). This approach is based on the better environmental behaviour of NRM30. The comparison between R22 and NMR30 has been developed on the basis of Coefficient of Performance (COP), temperature at compressor exit, power consumption per ton of refrigeration and volumetric refrigeration capacity variations, when evaporation temperature and condensation temperature increase. The above mentioned are calculated when the evaporation temperature varies in the range (-2, +10)° C and the condensation temperature varies in the range (40, 50)° C. The results reveal that COP increases with the increase of the evaporation temperature and the decrease of the condensation temperature- for both refrigerants. Although the ecological refrigerant (NRM30) shows an average COP value lower than the one of R22 (about 30% lower), NRM30 ensures an ecological operation of the plant and lower temperatures at compressor exit- which it is benefic for the long life of this machine. For the considered temperature ranges, the plant operates in efficient conditions for the higher value of the evaporation temperature (+10°C) and for the lowest value of the condensation temperature (40°C). For this conditions, it is seen that the vapours temperatures at the compressor exit are lowest, being ensured also the safe operation of the compressor.

RESEARCH OF THE EFFICIENCY OF MARINE DIESEL FUEL COOLING SYSTEM ON THE BASIS OF NEW REFRIGERANTS

The requirements of the International Maritime Organization, government environmental agencies and other non-governmental groups are aimed at reducing emissions of harmful substances into the environment during the operation of diesel engines. Among these substances, the most dangerous are sulfur oxide (SOx), nitrogen oxide (NOx) and particulate matter (PM). In accordance with the specified requirements, there is an active transition to fuels with ultra-low sulfur content. The use of these fuels in marine diesel engines is associated with a number of difficulties, because these engines are usually designed for operation on fuels with high viscosity and lubricity. The viscosity values for ultra-low sulfur fuels are close to the permitted minimums for diesel engines at normal engine room temperature. The greatest difficulties occur when the viscosity values fall below the specific range when the fuel temperature before the engine increases. For reliable operation of the engine, the fuel temperature must be constantly maintained at a range in which the fuel viscosity will have the required values. For this purpose the engine design provides presence of fuel cooling system with a water cooler and a chiller for heat removal from water. In this paper the efficiency of chiller refrigeration plant was investigated using new perspective refrigerant mixtures R125/R290 and R134a/R290 as working fluids in comparison with basic R134a and R22. The values of composition for both mixtures are chosen such that they are closest to the azeotrope. It is possible for azeotrope mixtures to minimize the temperature difference between heat exchanging medias in condenser and evaporator of refrigeration plant. During the investigation it was revealed that the values of refrigeration coefficient of refrigerating plant when using mixtures as working fluids were somewhat lower when operating on R134a and R22. But the values of volumetric refrigeration capacity with mixtures as working fluids are significantly higher.

Theoretical study on a modified single‐stage autocascade refrigeration cycle with auxiliary phase separator

Abstract In order to improve the cycle performance of a conventional single-stage autocascade refrigeration cycle (ARC), an auxiliary separator is considered to be introduced. In the modified autocascade refrigeration cycle (MARC), the auxiliary separator located after an expansion device is used to further collect the vapor enriched with low-boiling components. In this case, the MARC enables to improve the cycle performances by utilizing more zeotropic mixture enriched with the low-boiling components to realize a higher evaporation pressure at the given evaporation temperature in the evaporator of the cycle. The performances of the MARC and ARC are compared utilizing energy, exergy and exergo-economic analysis methods, and several important parameters are also discussed in detail. The results indicate that the MARC using zeotropic mixture R290/R170 is feasible and there are obvious improvements in terms of the COP, volumetric refrigeration capacity and exergy efficiency. It is found that compared to the ARC, the COP improvement of MARC can reach up to 16.1%. The exergy efficiency of MARC is increased by 10.23% and the overall cost rate of MARC is decreased by 2.51% under a typical operating condition. In addition, the COP of MARC has a maximum value at given conditions when the mass fraction of R290 at the compressor inlet is around 0.3. In general, the performance characteristics of the proposed cycle demonstrate its potential applications in low-temperature freezers.

Performance maximization by temperature glide matching in energy exchangers of cooling systems operating with natural hydrocarbon/CO2 refrigerants

• Temperature glide matching increases COP of hydrocarbon + CO 2 refrigeration systems. • Exergy destruction decreases in energy exchangers and increases in expansion valve. • Dimethyl ether + CO 2 and propylene + CO 2 blends have the highest performance. • Performance maximum is observed at a lower concentration of CO 2 in the blends. • A model is developed for temperature glide matching without experimental input. This research is part of an effort in finding viable alternative refrigerants to mitigate anthropogenic climate change. In this study binary zeotropic mixtures of selected hydrocarbons (HCs) with carbon dioxide (CO 2 ) are evaluated as alternative refrigerants for a vapor-compression refrigeration cycle. A thermodynamic analysis of these mixtures is performed for a cycle with a variable temperature of energy transfer fluid in both evaporator and condenser/gas cooler. A temperature glide matching method with a specified minimum temperature difference between refrigerant and energy transfer fluid in the energy exchangers was developed for performance maximization. This method does not require any experimental input or an educated guess for the temperature difference between refrigerant and energy transfer fluid and can simulate both sub-critical and trans-critical cycles. Performance metrics like the coefficient of performance (COP) and volumetric refrigeration capacity (VRC) are calculated and discussed for various mixture compositions (0 to 100% CO 2 ). Furthermore, non-dimensional exergy destructions in different components in the cycle are determined to estimate the effect of individual components on the total performance. An increase up to 40% in COP for zeotropic mixtures of HCs and CO 2 is observed when compared with pure HCs. The VRC is also shown to increase with increasing CO 2 concentrations in HC + CO 2 mixtures. Exergy analysis shows a decrease in non-dimensional exergy destruction in the energy exchangers due to temperature glide matching.

Theoretical energy performance assessment and environmental impact of various new ozone-friendly refrigerants used in residential air conditioners

This study focuses on energy performance investigation and environmental impact analysis of various new ecofriendly refrigerant blends as alternatives to high global warming potential refrigerant R22 theoretically. In this study, 23 refrigerants were considered at various composition. The present work considered the practical vapour compression refrigeration cycle for the performance assessment of various R22 alternatives. Essential studies such as toxicity, flammability, and total equivalent warming index of various novel refrigerants were also conducted in this study. Results obtained from practical vapour compression refrigeration cycle revealed that the energy efficiency ratio of refrigerants such as R1270 (2.860) and RB03 (R290/R152a of 60/40 in mass %) (2.854) was closer to the energy efficiency ratio of R22 (2.940). Volumetric refrigeration capacity (VRC) of R1270 (3293 kJ/m3) was similar to that of R22 (3297 kJ/m3) whereas VRC of RB03 (2908 kJ/m3) was almost similar to that of R407C (2925 kJ/m3) which was an alternative to R22. Compressor discharge temperature of RB03 was 15.78 ℃ lower when compared to R22. Flammability study revealed that all the new refrigerant blends (RB01 to RB04) were classified into weakly flammable (A2) and flammable (A3) category refrigerants whereas toxicity study revealed that all the investigated refrigerants were classified into non-toxic group (A). Refrigerant blend RB03 was less flammable compared to R1270. Total equivalent warming index analysis revealed that the environmental impact of R422A was 27.88% higher than R22 whereas RB03 has 4.97% lower environmental impact compared to R22. Overall, performance of refrigerant blend RB03 was better compared to 23 investigated refrigerants and it was very nearer to the performance of R22 and hence, it could be considered as an ecofriendly alternative to replace high global warming potential refrigerant R22 used in air conditioners.

Performance Analysis of an Ejector Enhanced Two-Stage Auto-Cascade Refrigeration Cycle for Low Temperature Freezer

In this paper, an ejector enhanced two-stage auto-cascade refrigeration cycle (EARC) using ternary mixture R600a/R32/R1150 is proposed for application of −80°C freezing. In EARC cycle, an ejector was employed to recover the expansion work in the throttling processes and lifted the suction pressure of the compressor. The performances of the ejector enhanced two-stage auto-cascade refrigeration cycle and conventional auto-cascade refrigeration cycle (CARC) were compared using thermodynamic analysis methods. The influences of the important operation parameters including mass fraction ratio of the mixture, fluid quality at the second separator inlet, condensation temperature, evaporation temperature, and expansion ratio of expansion valve on the performances of EARC cycle were discussed in detail. The results indicate that ternary mixture R600a/R32/R1150 has the optimal mass fraction ratio of 0.45/0.2/0.35 with respect to the maximum COP. The EARC cycle yields higher performance than the CARC cycle in terms of COP, exergy efficiency and volumetric refrigeration capacity. And 4.9%–36.5% improvement in COP and 6.9%–34.3% higher exergy efficiency could be obtained in EARC cycle comparing with CARC cycle. The finding of this study suggests that the EARC cycle has a promising application potential for low temperature freezing.

Thermodynamic Study on Blends of Hydrocarbons and Carbon Dioxide as Zeotropic Refrigerants

Abstract Finding alternative refrigerants is of extreme importance to mitigate anthropogenic climate change. Among the next-generation refrigerants, hydrocarbons (HCs) are of technical interest because they are natural, efficient, have low global warming potential (GWP), and zero ozone depletion potential (ODP). However, their flammability impedes their widespread usage for fire-safety reasons. The present work investigated zeotropic mixtures of hydrocarbons with carbon dioxide (CO2) as refrigerants for a simple vapor-compression refrigeration cycle, since their flammability risks are lower than those of pure hydrocarbons. Refrigerants were selected utilizing various screening steps based on environmental effects (such as GWP, ODP, and toxicity), thermophysical properties (such as critical temperature, and boiling point), and mixture data availability. The thermodynamic analysis for these selected zeotropic mixtures was performed for a cycle with a constant temperature of energy (heat) transfer fluid in both the evaporator and the condenser/gas cooler. Subsequently, performance parameters like the coefficient of performance and volumetric refrigeration capacity were compared for each of these blends at different operating conditions, and thus, the most promising hydrocarbon mixtures with CO2 were identified. As a result, the following four hydrocarbons, individually blended with CO2, were favorable in performance: propylene, dimethyl ether, propane, and isobutane. Further analysis was performed to determine the non-dimensional exergy destruction by the various components of the cycle.

Thermodynamic Performance Analysis of Hydrofluoroolefins (HFO) Refrigerants in Commercial Air-Conditioning Systems for Sustainable Environment

Global warming is one of most severe environmental concerns that our planet is facing today. One of its causes is the previous generation of refrigerants that, upon release, remain in the atmosphere for longer periods and contribute towards global warming. This issue could potentially be solved by replacing the previous generation’s high global warming potential (GWP) refrigerants with environmentally friendly refrigerants. This scenario requires an analysis of new refrigerants for a comparison of the thermodynamic properties of the previously used refrigerants. In the present research, a numerical study was conducted to analyze the thermodynamic performance of specifically low GWP hydrofluoroolefens (HFO) refrigerants for an actual vapor compression refrigeration cycle (VCRC) with a constant degree of 3 K superheat. The output parameters included the refrigeration effect, compressor work input, the coefficient of performance (COP), and the volumetric refrigeration capacity (VRC), all of which were calculated by varying the condenser pressure from 6 to 12 bars and vapor pressure from 0.7 to 1.9 bars. Results showed that R1234ze(Z) clearly possessed the desired thermodynamic performance. The drop in refrigeration effect for R1234ze(Z) was merely 14.6% less than that of R134a at a 12 bar condenser pressure; this was minimum drop among candidate refrigerants. The drop in the COP was the minimum for R1234ze(Z)—5.1% less than that of R134a at a 9 bar condenser pressure and 4.7% less than that of R134a at a 1.9 bar evaporator pressure, whereas the COP values of the other refrigerants dropped more drastically at higher condenser pressures. R1234ze(Z) possessed favorable thermodynamic characteristics, with a GWP of 7, and it can serve as an alternative refrigerant for refrigeration systems for a sustainable environment.