Ejector Expansion Refrigeration Cycle Research Articles

Dynamic simulation on operating modes of ejector in transcritical CO2 ejector expansion refrigeration cycles

This article proposes an ejector model based on the real properties of CO2, which includes the critical mode and sub-critical mode (the critical mode means the primary and suction flows are both choked, and the sub-critical mode refers to only the primary flow choking). Moreover, a dynamic model of the transcritical CO2 ejector expansion refrigeration cycle is developed to simulate system responses at different ejector operational modes. The prediction results by the ejector model and system model are compared with available experimental data, respectively. Furthermore, the dynamic responses of the ejector expansion refrigeration cycle based on the entire ejector model are compared with those predicted upon the ejector model only with critical mode. The present results show the entrainment ratio provided by the ejector model coincides well with the experimental data, and most data lie within ±10% error. The system model predicts the gas cooler pressure and evaporator pressure with errors of 1.8% and 4.2% for the measured results, respectively. Moreover, the pressure and mass flow rates of the system based on the ejector model only with critical mode are higher than that by the entire ejector model. The proposed model is useful to predict performances accurately and conduct dynamic analysis reasonably.

Dynamic model of a transcritical CO2 ejector expansion refrigeration system

This paper presents a dynamic model of a transcritical CO2 ejector expansion refrigeration cycle (EERC) which is a promising refrigeration system due to its environment-benign nature and low throttling loss. The mathematical models for gas cooler, evaporator and separator are formulated by using the mass and energy conservation equations. Based on the real properties of CO2, the ejector model is developed and the variable ejector component efficiencies are taken into account because they vary with operation conditions. The compressor and expansive valve are modeled in a set of algebraic equations. The presented transient simulation results are in good agreement with the experimental data. The dynamic behaviors of the system undergoing the change of expansion valve opening and ejector area ratio are observed by the developed model, which helps to understand the characteristics of the EERC and guide the system control.

Theoretical investigation on an ejector–expansion refrigeration cycle using zeotropic mixture R290/R600a for applications in domestic refrigerator/freezers

This paper presents a modified vapor–compression refrigeration cycle (MVRC) for applications in domestic refrigerator/freezers using zeotropic mixture R290/R600a. In the MVRC cycle, an ejector and a phase separator are added based on a traditional vapor–compression refrigeration cycle (TVRC) to improve the cycle performance. The coefficient of performance COP, volumetric cooling capacity, exergy loss and exergy efficiency are theoretically investigated for the MVRC cycle and compared with the TVRC cycle. The results show that the MVRC cycle outperforms the TVRC cycle under all given operating conditions and the advantage is more obvious at lower evaporating temperature, lower subcooling temperature and higher condensing temperature. Specifically, the COP and volumetric cooling capacity can be improved maximally by 16.71% and 34.97%, respectively. The exergy efficiency can be raised maximally by 6.71% and the total exergy loss can be reduced maximally by 24.47%. The further simulation results indicate that there exists an optimal mixture composition for the MVRC cycle that could obtain the maximum COP.

Energetic and Exergetic Analysis of an Ejector-Expansion Refrigeration Cycle Using the Working Fluid R32

The performance characteristics of an ejector-expansion refrigeration cycle (EEC) using R32 have been investigated in comparison with that using R134a. The coefficient of performance (COP), the exergy destruction, the exergy efficiency and the suction nozzle pressure drop (SNPD) are discussed. The results show that the application of an ejector instead of a throttle valve in R32 cycle decreases the cycle’s total exergy destruction by 8.84%–15.84% in comparison with the basic cycle (BC). The R32 EEC provides 5.22%–13.77% COP improvement and 5.13%–13.83% exergy efficiency improvement respectively over the BC for the given ranges of evaporating and condensing temperatures. There exists an optimum suction nozzle pressure drop (SNPD) which gives a maximum system COP and volumetric cooling capacity (VCC) under a specified condition. The value of the optimum SNPD mainly depends on the efficiencies of the ejector components, but is virtually independent of evaporating temperature and condensing temperature. In addition, the improvement of the component efficiency, especially the efficiencies of diffusion nozzle and the motive nozzle, can enhance the EEC performance.

Performance analysis of the ejector-expansion refrigeration cycle using zeotropic mixtures

To evaluate the performance of the ejector-expansion refrigeration cycle (EERC) using zeotropic mixtures, a numerical study is conducted. A constant-pressure two-phase ejector model for zeotropic mixtures is established. The effects of both the fluid composition and the working conditions are investigated. Mixture R134a/R143a is selected as the working and the simulation results reveal that, the cycle COP increases first and then decreases as MFt (the mass fraction of R134a) increases in the researched condition. The COP gets a maximum value of 4.18 with MFt of 0.9 and yields a minimum value of 3.66 with MFt of 0.5. With mixture 0.9/0.1, the COP improvement reaches a maximum value of 10.47%. This improvement rises at high condensing temperature or low evaporating temperature. The exergy analysis shows that the compressor and ejector contribute the most exergy destruction, and the cycle exergy efficiency achieves a maximum value with MFt of 0.7.

Thermodynamic study on a new transcritical CO2 ejector expansion refrigeration system with two-stage evaporation and vapor feedback

By the stability analysis of the basic transcritical CO2 ejector expansion refrigeration cycle (EERC), the paper proposed a new system which introduces another evaporator downstream the ejector to increase the gas quality into the separator and a vapor feedback valve to decrease the exceed gas into the compressor. The two new components stand for two different cycles: two-stage evaporation cycle and vapor feedback cycle. The theoretical analysis of the new system is carried out based on the first and second laws of thermodynamics to show the effect of the parameters on the system performance, such as entrainment ratio, high-side pressure, outlet temperature of gas cooler, etc. The results by the first law show that, compared with basic EERC the new system can be used in wider range of working conditions, and the COP of the two-stage evaporation cycle is 28.6% higher and the vapor feedback cycle is lower slightly. By exergy analysis at optimum high-side pressure, it is found that the exergy destruction of ejector is the greatest part. The simulation results also give the working ranges of the two cycles, which can help to analyze the system control. Hence, the improvement in the system is a promising method to reduce the restrain in basic EERC system but more study is still needed.

Thermodynamic Analysis of R410A Refrigeration Cycle with a Two-Phase Ejector

A thermodynamic analysis of the ejector expansion refrigeration cycle (EERC) was carried out based on a two-phase flow model. First the ejector parameter was optimized under the given condition. Then the influence of condenser temperature and evaporator was investigated. Numerical simulation result shows that the EERC always has a better performance than the basic system. When the evaporator is 0°C, the system COP can be improved by 18.6%.

Performance characteristics of R1234yf ejector-expansion refrigeration cycle

With a constant-pressure mixing ejector, the performance characteristics of an ejector-expansion refrigeration cycle (EERC) using R1234yf as refrigerant have been investigated. Also, the performance of R1234yf and R134a in the EERC has been compared. The study shows that, at condensing temperature of 40°C and evaporation temperature of 5°C, the coefficient of performance (COP) and volumetric cooling capacity (VCC) of the R1234yf EERC peak up to 5.91 and 2590.76kJ/m3, respectively. Compared with the standard refrigeration cycle the R1234yf EERC generally has a better performance, especially at the condition of higher condensing temperature and lower evaporation temperature. The COP and VCC improvements of the R1234yf EERC over the standard refrigeration cycle are also greater than that of the R134a cycle. In addition, the ejector design parameters including the pressure drop in suction nozzle, area ratio and component efficiencies on the R1234yf EERC performance have been analyzed.

Optimization of a novel carbon dioxide cogeneration system using artificial neural network and multi-objective genetic algorithm

In this research study, a combined cycle based on the Brayton power cycle and the ejector expansion refrigeration cycle is proposed. The proposed cycle can provide heating, cooling and power simultaneously. One of the benefits of such a system is to be driven by low temperature heat sources and using CO2 as working fluid. In order to enhance the understanding of the current work, a comprehensive parametric study and exergy analysis are conducted to determine the effects of the thermodynamic parameters on the system performance and the exergy destruction rate in the components. The suggested cycle can save the energy around 46% in comparison with a system producing cooling, power and hot water separately. On the other hand, to optimize a system to meet the load requirement, the surface area of the heat exchangers is determined and optimized. The results of this section can be used when a compact system is also an objective function. Along with a comprehensive parametric study and exergy analysis, a complete optimization study is carried out using a multi-objective evolutionary based genetic algorithm considering two different objective functions, heat exchangers size (to be minimized) and exergy efficiency (to be maximized). The Pareto front of the optimization problem and a correlation between exergy efficiency and total heat exchangers length is presented in order to predict the trend of optimized points. The suggested system can be a promising combined system for buildings and outland regions.

Energy and exergy analyses of a new combined cycle using carbon dioxide as working fluid

In this study, a new combined cycle based on the Brayton power cycle and the ejector expansion refrigeration cycle is proposed. The proposed cycle can provide simultaneous heating, cooling and power. And be driven by low temperature heat sources. The suggested cycle can save energy around 46% in comparison with a system producing cooling, power and hot water separately. Moreover, the second law efficiency of the combined system is around 30% which can be obtained under the given conditions. Finally, the surface area of the heat exchangers is determined. The suggested cycle can be a promising combined system for buildings and outland regions.

Theoretical study on a novel R32 refrigeration cycle with a two-stage suction ejector

This paper presents a new ejector enhanced vapor compression refrigeration cycle operating with the refrigerant R32. In this cycle, an ejector with two suction inlets is employed to recover the expansion process losses of the cycle. The theoretical model for the developed cycle is established and the performance of this cycle using refrigerant R32 is investigated. Furthermore, the performance comparisons of the developed cycle, basic vapor compression refrigeration cycle and conventional ejector expansion refrigeration cycle have also been carried out. The theoretical study shows that the developed cycle gives a higher cooling (heating) capacity and a higher coefficient of performance. The newly developed cycle could make a contribution for the application of refrigerant R32 in air-conditioner systems.

Performance characteristics of natural-refrigerants- based ejector expansion refrigeration cycles

The thermodynamic analyses and comparison of three natural-refrigerants-based vapour compression refrigeration cycles (ammonia, isobutane, and propane) are presented in this article using a constant pressure mixing ejector as an expansion device. Optimization of the area ratio of the ejector is done based on maximum cooling coefficient of performance (COP) and performance improvement for different operating conditions. The effect of using an internal heat exchanger is studied as well. Results show that optimum area ratio and cooling COP increases with a decrease in cycle temperature lift, whereas the COP improvement over basic expansion cycle increases with the increase in cycle temperature lift. Study shows that the optimum parameters, as well as performance using the ejector as an expansion device, are strongly dependent on the refrigerant properties as well as the operating conditions. The optimum area ratio is maximum for ammonia and minimum for propane, whereas maximum cooling COPs are similar. Using the ejector as an expansion device, propane yields a maximum COP improvement of 26.1 per cent followed by isobutane (22.8 per cent) and ammonia (11.7 per cent) for studies ranges. The effect of using an internal heat exchanger in the ejector expansion refrigeration cycle is found to be not profitable.

Effect of throat diameters of the ejector on the performance of the refrigeration cycle using a two-phase ejector as an expansion device

This paper is a part in a series that reports on the experimental study of the performance of the two-phase ejector expansion refrigeration cycle. In the present study, three two-phase ejectors are used as an expansion device in the refrigeration cycle. The effects of throat diameter of the motive nozzle, on the coefficient of performance, primary mass flow rate of the refrigerant, secondary mass flow rate of the refrigerant, recirculation ratio, average evaporator pressure, compressor pressure ratio, discharge temperature and cooling capacity, which have never before appeared in open literature, are presented. The effects of the heat sink and heat source temperatures on the system performance are also discussed.

Particular characteristics of transcritical CO 2 refrigeration cycle with an ejector

The present study describes a theoretical analysis of a transcritical CO 2 ejector expansion refrigeration cycle (EERC) which uses an ejector as the main expansion device instead of an expansion valve. The system performance is strongly coupled to the ejector entrainment ratio which must produce the proper CO 2 quality at the ejector exit. If the exit quality is not correct, either the liquid will enter the compressor or the evaporator will be filled with vapor. Thus, the ejector entrainment ratio significantly influences the refrigeration effect with an optimum ratio giving the ideal system performance. For the working conditions studied in this paper, the ejector expansion system maximum cooling COP is up to 18.6% better than the internal heat exchanger cycle (IHEC) cooling COP and 22.0% better than the conventional vapor compression refrigeration cycle (VCRC) cooling COP. At the conditions for the maximum cooling COP, the ejector expansion cycle refrigeration output is 8.2% better than the internal heat exchanger cycle refrigeration output and 11.5% better than the conventional cycle refrigeration output. An exergy analysis showed that the ejector expansion cycle greatly reduces the throttling losses. The analysis was also used to study the variations of the ejector expansion cycle cooling COP for various heat rejection pressures, refrigerant temperatures at the gas cooler exit, nozzle efficiencies and diffuser efficiencies.

Performance of the two-phase ejector expansion refrigeration cycle

This paper is a continuation of the authors’ previous work. The paper presents new experimental data of the system performance of the two-phase ejector refrigeration cycle (TPERC). The TPERC uses a two-phase ejector as an expansion device while the conventional refrigeration cycle (CRC) uses an expansion valve. The TPERC enables the evaporator to be flooded with refrigerant, resulting in a higher refrigerant-side heat transfer coefficient. The experimental study shows that the TPERC gives a higher cooling capacity and a higher coefficient of performance. Moreover, the pressure ratio and the discharge temperature of the compressor of the TPERC are lower than those of the CRC.