Ejector Expansion Refrigeration Cycle Research Articles

Dynamic analysis and control strategy of ORC coupled ejector expansion refrigeration cycle driven by geothermal water

Organic Rankine cycle combined ejector expansion refrigeration cycle (ORC-EERC) has significant potential for utilizing low-temperature heat. The study on dynamic response of the ORC-EERC combined system plays a particularly important role in optimizing the control strategy for the system, given the instability of the low-temperature heat source. In this paper, the ORC-EERC dynamic models with single and dual condensers are proposed. The simulation results show that the proposed improved model of EERC subsystem presents more accurate results relevant to the experiment system. The impact of the ORC subsystem on the refrigeration subsystem is more pronounced in the ORC-EERC system with a single condenser than in the system with dual condensers. In addition, the phenomenon of chocking in the ejector throat leads to the degradation of system performance when the heat source is disturbed. Therefore, a multi-device cooperative control strategy is proposed to enhance the safety and performance of the system. In the case study of geothermal water mass flow scheduling disturbance, the control strategy increases the cooling capacity of the system by a maximum of 9.29%.

Investigation of improvement potential of a double-efficient CO2 cooling and heating system using an ejector with advanced exergy analysis

This paper presents an improvement potential investigation of a double-efficient CO2 cooling and heating system using an ejector, which can operate in cooling or heating mode. For the first time, advanced exergy analysis is employed to offer improvement direction and guidance for the practical application of this novel system. Compared to the conventional exergy analysis, which is widely used in previous work, advanced exergy analysis can supply more information about the interaction among components and the avoidable exergy destruction under the technical constrains. Thus, more practical and accurate conclusions can be drawn. The results reveal that 74.56 % of the total exergy destruction is endogenous in cooling mode, demonstrating the weak interaction among components. The compressor should be given the highest priority for improvement, due to its largest sum of avoidable exergy destruction (17.71 W). The effect of ejector component efficiency is also discussed. As it varies from 0.5 to 0.9, the system exergy efficiency rises from 11.59 % to 14.18 %. Furthermore, the proposed system shows great advantage with 31.31 % less exergy destruction compared to ejector expansion refrigeration cycle. In heating mode, the compressor also deserves to be optimized first. But the expansion valve possesses no effort for improvement due to its negative sum of avoidable exergy destruction (−1.203 W).

Performances Investigation of the Eco-friendly Refrigerant R13I1 used as Working Fluid in the Ejector-Expansion Refrigeration Cycle

Knowing that from 2030 refrigerants used in refrigerating engineering should have a global warming potential (GWP) of less than 150. Searching for eco-friendly refrigerants with good performance and minimal environmental impact to substitute conventional working fluids such as R134a (GWP=1430) represents a great challenge for researchers.
 The present research aims to investigate and compare the performances of the eco-friendly refrigerant R13I1 (Zero GWP) used as a possible new working fluid in the ejector-expansion refrigeration cycle (EERC) with the commonly used R134a which has good performances but a high GWP. To reach this objective, a numerical program was developed using MATLAB software to evaluate the coefficient of performance (COP), the entrainment ratio (µ), the exergy destruction and the exergy efficiency for both refrigerants. Furthermore, the effect of the diffuser efficiency of the ejector on the COP and the compressor work was explored. Furthermore, the effect of the diffuser efficiency of the ejector on the COP, and the compressor work were explored. The simulation was realized for Tc selected between 30 and 55 °C and Te ranging between -10 and 10 °C. Results proved that the use of R13I1 as a working fluid in the EERC system exhibited a higher COP, µ, and exergy efficiency, as well as lower exergy destruction compared with R134a under the same operating temperatures. On another hand, the energetic analysis revealed that as Tc increases the COP and µ decrease. However, as Te varies from -10 and 10 °C, the COP and µ increase. Regarding exergy analysis, it should be noted that both exergy destruction and exergy efficiency are sensitively influenced by Tc more than Te. Overall, the study confirms that R13I1 could be a suitable substitute for the phase-out R134a in terms of performance and environmental protection.

Thermodynamic and economic analysis of refrigerant mixture R290/R1234ze used in an ORC-EERC system for low temperature heat sources

In the process of promoting carbon neutrality, heat driven refrigeration technology has been widely concerned due to its ability to make use of low-grade thermal energy and improve energy utilization. A novel combined organic Rankine cycle and ejector expansion refrigeration cycle (ORC-EERC) system is proposed in this study. To lower global warming potential and flammability, refrigerant mixture R290/R1234ze is chosen as the working fluid. The proposed ORC-EERC system with ejector and vapor–liquid separator are compared with those of the traditional organic Rankine cycle and vapor compression refrigeration cycle (ORC-VCC) by thermodynamic and economic analysis. The simulation results show that the ORC-EERC can achieve higher exergy efficiency and produce lower cooling temperature. Under typical conditions, the total coefficient of performance of ORC-EERC increased by 17.32% and its levelized cost of cooling decreased by 10.45% compared with the ORC-VCC. Furthermore, the ORC-EERC can remarkably improve performance at a lower freezing temperature or a higher condensing temperature. The results of the proposed cycle show that the ORC-EERC system has great application potential in freezers.

Energy and exergy analysis in the ejector expansion refrigeration cycle under optimum conditions

Refrigeration systems progress in parallel with the development of technology and the ways of saving energy in refrigeration systems are being researched. The literature suggests that incorporating ejectors in refrigeration systems can boost the coefficient of performance (COP) of the system. By utilizing ejector expansion, it is possible to improve the performance of the vapor compression refrigeration cycle (VCRC) by recapturing the expansion work that is typically lost during the expansion valve process. The present study investigation aims to contribute to the field of refrigeration by exploring the optimum pressure drop for three commonly utilized refrigerants. Specifically, the study scrutinizes the performance of an ejector based refrigeration cycle that incorporates a constant pressure mixing ejector. Utilizing the energy and exergy analyses are conducted to assess the system's performance with R134a, R600a, and R290 refrigerants across five distinct evaporator temperatures, namely 0°C, -5°C, -10°C, -20°C, and -30°C. The study further determines the optimum pressure drops in the secondary nozzle and the ejector area ratio at a specified condenser temperature, and examines the resultant total exergy destruction and exergy efficiency of the system. For R290 refrigerant; performance improvement ratio, decrease in total exergy destruction and exergy efficiency improvement ratios were found as 1.23, 54.02% and 22.97%, respectively. As a result, R290 is the most appropriate refrigerant for ejector expansion refrigeration cycle (EERC) among the refrigerants investigated as a result of the energy and exergy analyses.

Analysis of modified CO2 based combined power and ejector-expansion refrigeration cycle with dual evaporators activated by engine exhaust

ABSTRACT In this research, a combined system consisting of a supercritical CO2 Brayton cycle and an ejector-expansion refrigeration cycle with dual evaporators is presented with the aim to harness the engine exhaust heat effectively. Cascade ejectors are adopted to further reduce the destruction caused by the isenthalpic expansion process, which also can be considered as pressure recovery process. Comparative analysis in terms of thermodynamic and economic is performed between the previously reported system and the modified system under the combined power, refrigeration, and freezing mode (mode 1) and combined refrigeration and freezing mode (mode 2). It is found that improvements of 0.57% and 10.22% in exergy efficiency under mode 1 and mode 2 were achieved by the modified system, respectively, and the sum unit cost of product is reduced by 7.72% compared to the basic system. In the optimized condition, cooling capacities of 18.79 kW and 33.80 kW can be provided for refrigerated zone and freezing zone, respectively. And the exergy efficiency and sum unit cost of product of the system are 16.95% and 108.64 $/GJ, respectively, with a dynamic payback period of 4.994 years.

Performance analysis of a double-efficient CO2 cooling and heating system using an ejector

This paper presents a double-efficient CO2 cooling and heating system using an ejector, which can operate as modified dual-evaporators ejector expansion cycle (MDEEC) in cooling mode or as conventional heat pump cycle (CHPC) in heating mode through the reasonable arrangement of valves, and countercurrent heat transfer of CO2 with cooled or heated air is achieved in both modes. An ejector is utilized to recover the expansion work and two evaporators provide independent air dry-cooling and dehumidification in cooling mode. Two thermodynamic models are developed to investigate the effects of various parameters on the cycle performance. Comparison of proposed cycles with ejector expansion refrigeration cycle (EERC) and conventional dual-evaporator vapor compression cycle (CDVCC) are conducted based on energy analysis. The results show that coefficient of performance (COP) of this system is improved by more than 25% compared to EERC, and 33.62–56.27% compared to CDVCC. Besides, performance comparison of CHPC using CO2 and R134a is conducted, which reveals that COP of CO2 cycle is consistently higher, maintained above 2.7, and the maximum value is 5.36. The COP improvement is up to 29.74%, and the minimum value is 5.37%. This study provides a solution for efficient cooling and heating applying CO2 as refrigerant.

Energy and exergy analysis of a novel ejector-expansion refrigeration system based on condenser outlet split cycle

BackgroundIn this paper, the possibility of performance enhancement of a new Condenser Outlet Split (COS) cycle with the presence of two ejectors working in different temperatures is investigated. In order to enhance the cycle performance, an auxiliary ejector-expansion refrigeration cycle equipped with a separator and a secondary ejector has been employed, resulting in further performance improvement on both exergy and energy analyses on the different condenser and evaporator temperatures. MethodsThe thermodynamic equations of each component in the standard and proposed cycles have been solved in EES software. Significant FindingsThe auxiliary cycle boosted the pressure at the inlet of the secondary nozzle of the main ejector leads to a better performance of the proposed cycle. Through energy analysis, compressor work recovery increased by 12% and the coefficient of performance showed up to 14.1% enhancement. Through exergy analysis, our proposed cycle have been produced 6.8% reduction in exergy destruction compared to the standard cycle, and the total exergy performance of the given system can be increased from 8.2 to 14%.

Thermodynamic analysis of a novel multi-target temperature transcritical CO2 ejector-expansion refrigeration cycle with vapor-injection

In the present paper, a multi-target temperature ejector-expansion subcooler vapor-injection refrigeration cycle is proposed in order to improve the performance of natural fluid CO2 refrigeration cycles. A thermodynamics model to simulate a two-phase ejector cycle integrating a vapor-injection is first established from the energetic and exergetic perspectives. The behavior of the new cycle is then analyzed, and the adjustment direction of the cooling capacity and the evaporating temperature is pointed out. Furthermore, the new cycle is also compared with the subcooler vapor-injection refrigeration cycle and the ejector-expansion refrigeration cycle. The obtained results show that the behavior of the evaporators is affected by the bypass mass ratio and the entrainment ratio, and the two parameter determines the direction of adjusting the cooling capacity distribution and the evaporating temperature. The COP of the new cycle is about 17.9–29.4% and 2.8–7.8% higher than that of subcooler vapor-injection refrigeration cycle and ejector-expansion refrigeration cycle; the exergy efficiency of new cycle is about 14–28.2% and 3.7–11.3% higher than that of subcooler vapor-injection refrigeration cycle and ejector-expansion refrigeration cycle; and it is also found that the performance of the new cycle is improved more significantly under low cooling temperature and high ambient temperature conditions.

Influence of mixing section inlet and diffuser outlet velocities on the performance of ejector-expansion refrigeration system using zeotropic mixture

• Theoretical analysis of an ejector expansion refrigeration cycle . • Effects of mixing section inlet and diffuser outlet velocities on the system. • Effects of zeotropic mixture mass ratio on system performance. It is known that the performance of vapor compression cooling systems can be increased thanks to the ejector. In the literature, there are many studies on the subject, in which mathematical models of ejector-expansion cooling systems are developed. However, the refrigerant velocities at the mixing section inlet for the secondary flow (suction stream) and diffuser outlet were neglected in these studies. In the mathematical model used in this study, the velocities in both sections are considered and the system performance is calculated. The performance assessment of an ejector-expansion refrigeration system was realized in the case of using the R600a/R290 refrigerant mixture as a working fluid. Thus, the effect of zeotropic refrigerant mixtures on the system performance is also investigated, considering the refrigerant velocities at the mixing section inlet and diffuser outlet. According to the obtained results, it has been found that the cooling performance of the system that uses R600a/R290 mixture as a refrigerant is 5.8%-7% higher when the velocities at the mixing section inlet and diffuser outlet are considered compared to the neglected one. The exergy efficiency is also calculated to be around 4.6% lower when the ejector mixing section inlet and diffuser outlet velocities are neglected.

Multi-mode operation and thermo-economic analyses of combined cooling and power systems for recovering waste heat from data centers

Current solutions for waste heat recovery from data centers are mainly district heating and refrigeration. However, intermittent demand for space heating and cooling resulted from seasonal or spatial variations makes inefficient utilization of waste heat. To better harvest the low-grade thermal energy in data centers, combined cooling and power systems are proposed, with the capability of adjusting the energy output to meet diverse energy demands hourly and seasonally. In total, six cogeneration systems with different configurations are investigated, with the power cycles being either organic Rankine cycle or Kalina cycle, and the refrigeration cycles being vapor compression refrigeration cycle, ejector expansion refrigeration cycle or absorption refrigeration cycle. Depending on the energy demands of data centers, each system has three operation modes: combined cooling and power, power alone and cooling alone. The performance is evaluated in terms of both the thermodynamic and economic performance by parametric study and multi-objective optimization. Results show that the organic Rankine cycle/absorption refrigeration cycle hybrid system has the best thermal-economic performance in all three modes. According to the comprehensive evaluation of the TOPSIS method and the entropy weight method, the energy efficiency at the optima is 58.13%, and the unit cost of product is 4.25 $/GJ, with the net power output of 4.25 kW and the cooling capacity of 150 kW.

Performance investigation of an ejector expansion refrigeration system working on different alternative refrigerants to R134a

ABSTRACT In this paper, the performance characteristics of an ejector-expansion refrigeration cycle using six low GWP alternative refrigerants for R134a are presented through the first and second laws of thermodynamics. The ejector is modelled by assuming a constant-mixing pressure. The investigated refrigerants are compared based on the optimum ejector area ratio, discharge temperature, volumetric cooling capacity (VCC), coefficient of performance (COP) and exergy efficiency (ηex). The drop-in analysis is considered based on the same operating/designing parameters, and the VCC, COP and ηex improvements over the conventional refrigeration cycle are presented. The improvements in COP and VCC are between 7.914%–18.46% and 5.712%–22.82%, respectively, for the investigated range of evaporating and condensing temperatures. These values are higher than that of R134a by about 21% and 16%, respectively. The VCC using R1234yf is very close to R134a with a maximum reduction of 6.5%. Therefore, R1234yf refrigerant appears to be the best alternative to R134a in an ejector-expansion system with an appreciable COP and ηex devaluation. R152a outperforms R134a in terms of COP and ηex, thus it is a suitable alternative to R134a except for safety.

A Comparative Performance Study of an Ejector-Expansion Refrigeration Cycle Using R134a and its Alternatives: Application of Automobile Air Conditioning

In this study, the performance of ejector-expansion refrigeration cycle (EERC) with R134a alternative refrigerants (R152a, R1234yf, R404A, R407C, R507A and R600a) for automobile air-conditioning application is investigated numerically. The ejector is modeled with a constant mixing-pressure assumption taking into consideration the friction effect in the ejector mixing section. The studied refrigerants are compared based on the optimum area ratio, discharge temperature, compressor input power, volumetric cooling capacity, exergy destruction, COP, exergy efficiency and COP improvement. The results show that R152a and R1234yf have the closest performance to R134a and can be considered the most suitable alternative refrigerants for R134a. The COP and exergy efficiency are improved by 2.26% and 2.27%, respectively, using R152a compared to the use of R134a, whereas they are reduced by 2.89% and 2.88% using R1234yf. The volumetric cooling capacity is reduced for both R152a and R1234yf by 6.14% and 6.8%, respectively. In addition, the effect of compressor rotational speed on the performances is reported.

A Comprehensive Energetic and Exergetic Analysis of an Ejector Expansion Refrigeration Cycle Using R22 and R410A

In this paper, the performance characteristics of an ejector-expansion refrigeration cycle (EERC) using R410A are investigated in comparison with that using R22 based on first- and second-law perspectives. For this purpose, a numerical model of constant mixing pressure is developed and a parametric study of the effective design parameters is implemented. The results show that at evaporation temperature ([Formula: see text]) and condensing temperature ([Formula: see text]) equal to [Formula: see text]C and [Formula: see text]C, respectively, the coefficient of performance (COP), exergy efficiency and volumetric cooling capacity (VCC) of the R410A EERC is improved by 12.91%, 12.89%, and 10.8%, respectively. Compared with the conventional refrigeration cycle, the EERC is more beneficial at lower evaporation temperature and higher condensing temperature. The COP of R410A EERC, exergy efficiency and VCC improvements over the regular refrigeration cycle are also greater than that of R22 by about 34.7%, 32.3% and 31%, respectively. Exergy analysis shows that applying an ejector in lieu of a throttle valve improved the energetic efficiency by 7.793–15.42% and by 10.59–22.79% for R22 and R410A, respectively, for the given range of evaporating and condensing temperature. In addition, the effects of the suction nozzle pressure drop, area ratio and the component efficiencies of the ejector on the EERC performance are analyzed.

Thermoeconomic analysis of CO2 Ejector-Expansion Refrigeration Cycle (EERC) for low-temperature refrigeration in warm climates

Refrigeration industry is adopting a proactive strategy to phase out fluorinated greenhouse gases by more sustainable working fluids. R744 is a natural refrigerant widely proposed for commercial refrigeration. Its use in cascade and booster cycles allows a combined cooling and freezing production. However, when single-stage evaporation at low temperature is required, the adoption of R744 in transcritical cycles is scarce. The main reasons are due to the low Coefficient of Performance (COP) achieved, as well as the technical limitations to reach extreme pressure ratios using commercial compressors. In light of this, this paper proposes to use the CO2 Ejector-Expansion Refrigeration Cycle (EERC) to overcome these drawbacks. To assess the feasibility of the proposal, a thermoeconomic optimization is conducted for low-temperature refrigeration in warm climates. The analysis has been conducted considering a two-phase flow ejector, a commercial double-stage compressor, and evaporating conditions ranging from −10 °C to −38.11 °C, which was revealed the minimum temperature to avoid the triple point inside the ejector. The results showed that the EERC allows using smaller commercial compressors within a broader operating envelope, improving the annual average COP about 5.5% compared to the reference cycle, besides reducing investment and yearly energy consumption costs.

Thermodynamic analysis of a combined supercritical CO2 and ejector expansion refrigeration cycle for engine waste heat recovery

An engine waste heat driven combined power and refrigeration system, comprised of a regenerative supercritical CO2 Brayton cycle (RSCBC) and an ejector expansion refrigeration cycle (EERC), is proposed. In this system, the RSCBC is adopted as the topping cycle to generate power by recovering the high-temperature waste heat of engine. Meanwhile, the power is utilized by the compressor in the EERC. Such a waste heat recovery system can not only decrease the specific fuel consumption, but also provide refrigeration for refrigerated trucks to realize food preservation. Energy and exergy analysis are conducted on the RSCBC/EERC. The performance of four zeotropic mixtures used in EERC and different mixture compositions are compared. Moreover, the effects of several significant operating parameters are discussed in detail, including turbine inlet pressure and temperature, compressor inlet pressure and temperature, pressure drop in the ejector, evaporating temperature, and condensing temperature. To investigate the influence of the installation of the RSCBC/EERC system, weight estimation analysis is conducted. The results show that the refrigerating capacity and COPcomb of the system with R32/CO2 (0.9/0.1) are up to 225.5 kW and 2.05, respectively. And the equivalent power loss due to the additional weight is estimated to be 5.21 kW. In general, the RSCBC/EERC has proven its application potential in recovering waste heat to provide refrigeration through thermodynamic analysis.

Performance evaluation of a modified R290 dual-evaporator refrigeration cycle using two-phase ejector as expansion device

This paper presents a modified dual-evaporator ejector expansion refrigeration cycle (MDEEC) in which a two-phase ejector is used as the expansion device to recover the expansion work. Based on constant-pressure mixing theory, a thermodynamic model is developed to investigate the effects of various parameters on the system performance. Also a comparative study of the modified cycle with a conventional one (CDVCC) and a previous ejector cycle (COSEC) is conducted in terms of energy and exergy analysis. The results show that COP of the modified cycle is improved by about 10% and the exergy destruction of expansion device is reduced by more than 90% compared with the COSEC. At the operating condition of Tc = 45 °C and Te2 = 5 °C, the COP and exergy efficiency of the MDEEC can reach 6.515 and 0.3184, respectively, which are 42.6% and 36.7% higher than those of the CDVCC. It is also revealed the performance improvements become more significant at higher condensing temperatures or lower evaporating temperatures. Finally, the effects of the ejector components efficiency and the performance under off-design conditions are discussed.

Performance assessment of a low-grade heat driven dual ejector vapour compression refrigeration cycle

In the present study, an ejector expansion refrigeration cycle is modified by placing a low-grade heat driven ejector between the compressor exit and the condenser inlet to reduce the secondary energy consumption. This modified cycle is designated as dual ejector vapour compression refrigeration cycle. The condenser temperature is assumed to be 308 K. R32 and R1234yf are considered as working fluids due to their lower global warming potentials and lesser flammability compared to hydrocarbons. The result indicates that for each of the considered working fluids, there is an optimum compressor pressure ratio corresponding to which mechanical COP (Coefficient of performance) is a maximum. It is observed that using combinations of the heat driven ejector and the compressor, mechanical COPs are 25.7% and 37.2% higher compared to those of ejector expansion refrigeration cycles operating with R32 and R1234yf respectively for an evaporator temperature of 263 K. Corresponding heater exit temperatures are found to be 338 K (for R32) and 348 K (for R1234yf). Mechanical COP of the proposed dual ejector cycle is also higher than that of the vapour compression cycle operating with single heat driven ejector.

Performance assessment of an ejector enhanced dual temperature refrigeration cycle for domestic refrigerator application

Recently, more than 10% energy saving potential was experimentally demonstrated in the condenser outlet split ejector expansion refrigeration cycle when compared with a conventional refrigerator. Nevertheless, introducing two-phase refrigerant into the evaporator causes excessive pressure drop, and compression of redundant vapor counteracts the ejector performance. To overcome these challenges, a modified cycle is proposed by adding a separator to minimize vapor feeding into the low-temperature evaporator. A cycle model is developed and verified by experimental data achieving 10% accuracy. Theoretical investigations of the new cycle indicate 7.7% and 5.5% efficiency and volumetric cooling capacity improvement comparing with the conventional condenser outlet split cycle at nominal conditions. Impacts of evaporating temperature, condensing temperature, pressure drop of the evaporator, heat recovery effectiveness, and separator efficiency are discussed. This study offers an option to further improve energy efficiency for the dual temperature domestic refrigerator.

Thermodynamic Analysis of Transcritical CO2 Ejector Expansion Refrigeration Cycle with Dedicated Mechanical Subcooling

The new configuration of a transcritical CO2 ejector expansion refrigeration cycle combined with a dedicated mechanical subcooling cycle (EMS) is proposed. Three mass ratios of R32/R1234ze(Z) (0.4/0.6, 0.6/0.4, and 0.8/0.2) were selected as the refrigerants of the mechanical subcooling cycle (MS) to further explore the possibility of improving the EMS cycle’s performance. The thermodynamic performances of the new cycle were evaluated using energetic and exergetic methods and compared with those of the transcritical CO2 ejector expansion cycle integrated with a thermoelectric subcooling system (ETS). The results showed that the proposed cycle presents significant advantages over the ETS cycle in terms of the ejector performance and the system energetic and exergetic performances. Taking the EMS cycle using R32/R1234ze(Z) (0.6/0.4) as the MS refrigerant as an example, the improvements in the coefficient of performance and system exergy efficiency were able to reach up to 10.27% and 15.56%, respectively, at an environmental temperature of 35 °C and evaporation temperature of −5 °C. Additionally, the advantages of the EMS cycle were more pronounced at higher environmental temperatures.