Ejector Area Ratio Research Articles

Investigation on improvement potential of steam ejector performance in refrigeration cycle via constant rate of momentum change design method

In this paper, an ejector created by the constant rate of the momentum change method (CRMC ejector) was experimentally studied and compared with the widely used constant pressure method (CPM ejector) under the same ejector area ratio. The influence of the boiler temperature, evaporator temperature, and primary nozzle size on the ability to improve the performance of the CRMC ejector was examined. The results indicated that at the same ejector area ratio, the CRMC ejector always performed a higher mass entrainment ratio than the CPM ejector. However, the critical condenser pressure was similar. The average percent improvement of the entrainment ratio via the CRMC ejector was approximately 20%. Based on the photograph taken from the transparent ejector, a compression shock wave was still found in the flow process of the CRMC ejector. This shows that an improvement potential of the CRMC ejector does not concern the compression shock wave as proposed in the design theory. The key to improvement was believed to be its ability to mitigate the momentum loss during the mixing process. In such a case, some simulation works based on computational fluid dynamics (CFD) were employed for explanation. This can also confirm that the compression shock wave via CRMC ejector is still found. In addition, this paper compared the experimental results with the theoretical results obtained from 1-D theory and CRMC theory to alternatively discuss that an improvement potential of the CRMC ejector was mainly the cause of a lower mixing loss.

Advanced exergy analysis of a solar-driven cascade ejector system with heat storage

Solar-driven cascade ejector system can not only promote the utilization reliability of the solar energy, but also improve the performance of solar energy systems. This paper proposes a novel solar-driven cascade ejector system which integrates a solar ejector heat storage subsystem with R290 as refrigerant and a transcritical CO2 ejector-expansion refrigeration subsystem. The conventional and advanced exergy analysis methods are utilized to investigate the system’s exergetic performance, and explore the interactions among the system components and their improvement potential. The effects of compressor efficiency, area ratio and efficiency of ejectors on the exergetic performance of system and components are investigated. The analysis results show that the transcritical CO2 ejector-expansion refrigeration subsystem has higher exergy efficiency and its components have small exogenous exergy destruction. The endogenous exergy destruction and the avoided exergy destruction of cascade system account for 88.85% and 41.46%, respectively. Besides, 66.35% of exogenous exergy destruction of middle heat exchanger is caused by the compressor and CO2 ejector, and to improve the performance of CO2 ejector and CO2 evaporator would decrease the exergy destruction of compressor. CO2 ejector and R290 ejector have the superior improvement potential in each subsystem compared to other components. The rise of ejector area ratio would increase the endogenous exergy destruction of ejector. For the system with high-performance compressor, R290 ejector efficiency should be attracted more attention to reduce its avoided endogenous exergy destruction.

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.

Thermodynamic optimisation of a booster-ejector vapour compression refrigeration system using solar energy and R152a/Cu nano-refrigerant

Conventional vapour compression refrigeration systems require high electrical energy for low temperature applications. For the first time in the literature to reduce this required energy, comprehensive thermodynamic analysis and optimization of booster-assisted ejector expansion vapour compression refrigeration system with R152a/Cu nano-refrigerant are presented for low-temperature applications. Solar panels are used to cover the total compressor work, using the climate data of Izmir, Turkey. According to the thermodynamic optimization findings, the use of nanoparticles in the refrigeration system led to several improvements when compared to the R152a refrigeration system. These enhancements include a reduction of 6.52-11.71% in the main compressor discharge temperature, a decrease of 18.46-34.48% in the total exergy destruction rate, an increase of 3.08-4.04% in the entrainment ratio, a reduction of 0.089-3.25% in the ejector area ratio, a decrease of 8.34-14.27% in the panel area, and an increase of 8.09-14.05% in both the coefficient of performance and exergy efficiency. Another thing worth mentioning is that coefficient of performance and exergy efficiency improved by 2.06% and 1.96%, respectively, while total exergy destruction reduced by 4.83% compared to our previous study. The results obtained from the thermodynamic optimisation provide a useful reference for the design of an experimental system, as they provide evidence of model validity and can guide the implementation of the system.

Investigation of steam ejector parameters under three optimization algorithm using ANN

Several industries have adopted Steam ejectors as promising energy-saving devices. The steam ejector is used extensively in the HVAC, refrigeration, and desalination industries because it harnesses surplus heat. Numerous computational fluid dynamics (CFD) and thermodynamic models have been addressed in the academic literature. Predictions for steam ejector parameters using these models are fairly accurate. However, considerable discrepancies between experiments and models are sometimes as high as 20 %. Contrarily, CFD simulations for an ejector are computationally expensive and necessitate careful selection and tweaking of the turbulence model. ANN-based data-driven techniques are now used for complicated mechanical system modeling. The advantages of a well-trained ANN model include low computational costs and adaptability for integration with real-time control systems. In this study, we developan artificial neural network (ANN) model of a steam ejector and analyzes how different training strategies affect the ANN model's ability to make accurate predictions. The model is trained using a sizable experimental library with various geometrical and operational conditions. Using a typology of four input factors (Nozzle Throat Diameter (Ntd), Diffuser Outlet Diameter (Dod), Ejector Area Ratio (σp), and Entrainment Ratio (ER)) that capture geometry and operating conditions characteristics, the framework predicts two output parameters: (a) Coefficient of performance (COP) and (b) Pressure reduction ratio (PRR) of the steam ejector. Among the three optimizers tested for algorithm training, the ANN model trained using the ADAM optimizer performed the best. The model's hidden layer contains 102 neurons, and a split ratio of 0.2 is used during dataset training. The average error for COP and PRR predictions made by the ANN model is ± 1.8 % and ± 2.4 %, respectively. As a result, the ANN model can be used to improve the steam ejector system's configuration and operation.

Exergoeconomic Analysis of a Variable Area Solar Ejector Refrigeration System under Hot Climatic Conditions

The present study investigates low-grade heat utilization in ejector refrigeration systems under hot climatic conditions. A variable area ejector is used to maximize the harvested heat from the generator of the solar system at peak times. Exergy, economic, and exergoeconomic analyses are conducted to evaluate the performance of the system. A thermodynamic model of the system has been developed using Ebsilon Professional software. Available experimental and theoretical data validate the results. The effects of properties of the working fluids, ejector geometry, and operation conditions are also evaluated. It was found that the coefficient of performance of the system reached 0.45 at a generator pressure of 3 bars. Furthermore, it was noticed that the overall exergy efficiency could be increased for a fixed generator temperature while increasing the ejector area ratio. A value of 21% exergetic efficiency was calculated for the system. The exergoeconomic analysis of the system demonstrated that heat exchangers are required to be improved thermodynamically at the expense of the capital investment cost.

Performance investigation for CRMC and CPM ejectors applied in refrigeration under equivalent ejector geometry by CFD simulation

In this paper, one of the remaining questions for ejector design, “Does the constant rate of momentum change (CRMC) ejector provide better performance than the constant pressure mixing (CPM) ejector under identical ejector area ratio, ejector length, and operating conditions?”, has been answered. Two steam ejector designs operating with the various boiler and evaporator temperatures were simulated by the SST k-omega turbulence model. The present computational fluid dynamics (CFD) model produced a reasonable agreement with our previous published experimental data. The upstream operating conditions were simultaneously considered to assess the better performance ejector design with the help of the primary expansion coefficient. The predicted results revealed that the CRMC ejector showed an advantage in entrainment ratio and a disadvantage in critical condenser pressure. However, the ejector efficiency comparison confirmed that the CRMC ejector design provided better performance than the CPM ejector design for a primary expansion coefficient greater than unity. The maximum percentage improvement of ejector efficiency was 32.418%.

Experimental Determination of an Optimal Performance Map of a Steam Ejector Refrigeration System

An experimental determination of optimal performance of a steam ejector refrigerator was proposed which aims to indicate the optimal performance under various heat source temperatures. A small-scale steam ejector refrigerator test bench was constructed to carry out the experiment and to determine the optimal performance map. Three primary nozzles with throat diameters of 1.4, 1.6, and 1.8 mm, were tested with an ejector throat diameter of 14.5 mm, providing the ejector area ratios of 107, 82, and 65, respectively. For a particular working condition, the boiler temperature was varied to determine the maximum COP which is recognized as the optimal operation. It was found that the secondary fluid stream is first choked at the optimal boiler temperature. This optimal point varied significantly with the evaporator temperature, condenser pressure, and ejector area ratios. It was found that this steam ejector refrigerator could be operated under the optimal boiler temperature between 102.5 and 117.5 °C depending on the ejector area ratio, evaporator temperature, and condenser pressure. The optimal performance map is beneficial to further control the heat source temperature so that the maximum COP is achieved.

Advanced exergy analysis of a CO2 two-phase ejector

Ejector is meaningful and valuable to improve the transcritical CO2 refrigeration system. To study in-depth on the exergy destruction is significant for the performance enhancement of CO2 ejector. This paper presents a comprehensive investigation on the exergetic performance of CO2 two-phase ejector using conventional and advanced exergy analysis method to explore the interactions among ejector components and their improvement potential. The effects of primary flow pressure, suction flow temperature and area ratio (motive nozzle throat area to mixing chamber area) on the ejector exergy destruction are discussed. The results indicate the largest exergy destruction in the ejector is caused by the mixing chamber, followed by the motive nozzle, diffuser and suction chamber. Based on the avoidable exergy destruction rate and exergy destruction proportion, the order of optimization potential for ejector components is motive nozzle, diffuser, mixing chamber and suction chamber. However, the sum of avoidable exergy destruction of mixing chamber is the largest, which has the highest priority for improvement of overall ejector performance. The exogenous exergy destructions of the mixing chamber and diffuser are largely caused by the motive nozzle, and the exergy destructions would be increased with the improvement of motive nozzle performance. There exists an optimal primary flow pressure 9.5 MPa to minimize the exergy destruction of the each component of the ejector. To reduce the suction flow temperature and the ejector area ratio can decrease the avoidable exergy destruction of the components. Moreover, the variation of operating parameter has no effect on the optimization sequence of the overall ejector and its components. This work would provide a helpful way to guide the optimization on the ejector efficiency.

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.

Thermodynamic performance enhancement of booster assisted ejector expansion refrigeration systems with R1270/CuO nano-refrigerant

Ejector expansion refrigeration systems have gained prominence in the refrigeration sector, providing much better thermodynamic performance than conventional refrigeration systems. The present work aims to improve the thermodynamic performance of a booster assisted ejector expansion vapour compression refrigeration system with constant area mixing theory for low-temperature applications using R1270/CuO nano-refrigerant. Comparative energy and exergy based thermodynamic analysis of pure refrigerant and nano-refrigerant (2 wt% of CuO to R1270) systems are carried out. The pressure drop in the receiver part of the ejector and pressure ratio of the booster compressor are optimized for different operating conditions. The optimized results pointed out that the system using nano-refrigerant is the best one for which the proposed system has 8% lower discharge temperature of the main compressor, 0.59% lower ejector area ratio, 3.23% lower entrainment ratio, 8.93% higher exergy efficiency, 8.96% higher COP (Coefficient of Performance) and 21.23% lower total exergy destruction than pure refrigerant-based system at a condenser temperature of 45 °C and an evaporator temperature of −30 °C. Furthermore, there is a minimum COP improvement of 14.42% and a maximum COP improvement of 29.32% compared to research studies in the literature under identical operating conditions. The proposed calculation procedure has maximum deviation of 4.17% compared to experimental studies in the literature. Therefore, it can serve as a useful guide for performing the theoretical analysis of nano-refrigerant based ejector expansion refrigeration systems before setting up an experimental system.

Effect of mixing chamber length on ejector performance with fixed/varied area ratio under three operating conditions in refrigerated trucks

In this paper, an ejector-based multi-evaporator refrigeration system is proposed to provide three switchable operating modes of refrigerated trucks, namely, refrigerating – freezing (R-F), air-conditioning – freezing (A-F) and air-conditioning – refrigerating (A-R) modes. Under these three operating modes, CFD simulations are conducted to evaluate the optimum ejector constant-pressure mixing chamber length (Lpm) and constant-area mixing chamber length (Lam) as well as the sum of these two lengths (Lpam) with fixed and varied ejector area ratio (AR, which is expressed as ratio of the cross-sectional area of constant-area mixing chamber to primary nozzle outlet area). The results show that: (1) optimization of Lpm and Lam has small effect on ejector entrainment ratio (ER, which is defined as the ratio of secondary mass flow rate to primary mass flow rate) with fixed AR of 3 under three operating modes, and the maximum increment of ER are 0.0752, 0.0884 and 0.0205 for R-F, A-F and A-R mode, respectively; (2) under varied AR, when optimizing Lpm and Lam, the increment of ejector ER is 1.615, 2.249 and 0.021 for R-F, A-F and A-R modes, respectively; (3) the optimal Lpm and Lpam of the ejector increase first and then decrease with the increase of AR, however, the optimal Lam is irregular with the increase of AR; (4) compared with Lpm and Lam, the effect of AR on ejector performance is the most prominent when AR gets larger. The novelty of this study is that the relations between the optimal mixing chamber length and varied AR are identified.

Performance improvement of ejector refrigerator–based water chiller working with different mixing chamber profiles

This paper proposes the performance improvement of the ejector refrigerator based water chiller (ejector-based chiller) by means of using different mixing chamber profiles. Two different ejector mixing chamber profiles are constructed which are based on the conventional method (CONV–ejector) and the constant rate of momentum change method (CRMC–ejector). With the different design methods, the ejectors have different flow areas along the ejector’s axis; however, they have identical ejector throat diameters of 9 mm. Both ejectors are equipped with two primary nozzles, and hence, they have the same ejector area ratio of 6.3 and 7.9, respectively. The refrigerator is powered by hot water at a temperature of 94–98 °C while the condenser is cooled by cooling water at 29–31 °C. The chilled water temperature (Tchill) under various cooling loads and COP is assessed. It is found that the CRMC–ejector produces a much lower chilled water temperature than the CONV–ejector at identical cooling load. The system COP can be increased by 27–63% via the CRMC–ejector. With the change in Thot, both ejectors produce identical Tchill; however, the CRMC–ejector still produces much lower Tchill at an identical cooling load. A larger primary nozzle throat yields a higher Tchill.

Numerical study on the auxiliary entrainment performance of an ejector with different area ratio

In this paper, an ejector-based multi-evaporator refrigeration system is proposed for the tropical region refrigerated trucks. CFD simulations are performed to study the auxiliary entrainment effect of the ejector operated in air-conditioning - freezing mode. First, the performance of the ejector with various auxiliary hole position in different chambers is investigated. Then, based on the optimal auxiliary hole position of each chamber, the influence of double and triple auxiliary holes on the ejector performance is identified. Next, optimal angle with the optimized auxiliary hole position is determined. Last, the effect of the ejector area ratio on optimal auxiliary hole position, angle and entrainment ratio is evaluated. The main results show that: (1) Optimal auxiliary hole position is 59.5 mm or the length ratio of distance between the inlet of constant-area mixing chamber and the auxiliary hole center point to the length of the constant-area mixing chamber is 1.90, and optimal auxiliary hole angle is 45°; (2) The effect of the auxiliary hole position on the ejector performance is stronger than the auxiliary hole angle; (3) the optimum auxiliary hole position, angle as well as entrainment ratio are affected by the ejector area ratio.

Experimental Investigation of the Performance and Spray Characteristics of a Supersonic Two-Phase Flow Ejector with Different Structures

A two-phase flow ejector is an important part of a water mist fire suppression system, and these devices have become a popular research topic in recent years. This paper proposes a supersonic ejector that aims to improve the efficiency of water mist fire suppression systems. The effects of ejector geometric parameters on the entrainment ratio (ER) were explored. The effects of primary flow pressure (PP) on the mixing process and flow phenomena were studied by a high-speed camera. The experimental results show that the ER first increases and then decreases with increasing PP. ER increases with increasing ejector area ratio (AR). The PP corresponding to the maximum ER of ejectors with a different nozzle exit position (NXP) is 3.6 bar. The ejector with an NXP of +1 and AR of 6 demonstrate the best performance, and the ER of this ejector reaches 36.29. The spray half-cone angle of the ejector increases with increasing ER, reaching a maximum value of 7.07°. The unstable atomization half-cone angle is mainly due to a two-phase flow pulsating phenomenon. The pulsation period is 10 ms. In the present study, a general rule that provides a reference for ejector design and selection was obtained through experiments.

Study on Conceptual Design of a Solar Ejector Refrigeration System

The refrigeration system based on the conventional compression cycle consumes an enormous amount of high-grade energy. Using fossil fuels as the energy sources results in the addition of CO2into the atmosphere and consequently stimulating higher greenhouse effect. The ejector refrigeration systems powered by renewable energy sources would be an effective alternative without increasing global CO2footprint. In this study, the performance characteristics of a solar ejector refrigeration system working with R718 are analytically calculated by using a one-dimensional flow model. At the critical mode, the solar ejector-refrigeration system is analyzed at various working conditions such as condenser temperature, evaporator temperature, generator temperature, and ejector area ratio. The critical system performance is analyzed to meet any designated working conditions with a wide range of condenser temperatures. It is found that during the critical mode of operation, higher area ratio, higher evaporator temperature and lower generator temperature enhance the performance of the system. The minimum evaporator temperature, and the maximum generator temperature designed to acquire the required coefficient of performance value are also calculated.

Performance of ejector refrigeration cycle based on solar energy working with various refrigerants

The refrigerator unit based on electrically driven vapor compression technology consumes high energy, associated with high cost and loss of ecosystem. Recently, solar thermal energy emerges as a key research area and introducing it in refrigerator application has happened extremely fast. Solar thermal refrigeration systems based on ejector compression technology are thriving because of its utilization of low-grade energy sources, straight forward design, non-moving parts, lower maintenance costs, and durability. In this present work, the performance of a solar ejector refrigeration system (ERS) is calculated analytically using one-dimensional model. The performance parameters are calculated with the assumption that both the condensation and evaporation processes occur along the saturation line. Initially, the influence of the ejector area ratio, generator temperature, condenser temperature, and evaporator temperature on the performance of the ERS is analyzed in critical mode with water (R718) as the working fluid. The analysis shows that the coefficient of performance increases more than two times on increasing the ejector area ratio from 6.4 to 12.8. The results also show that a higher coefficient of performance (COP) is obtained at a higher ejector area ratio. The COP is found to be inversely related to the generator temperature, meanwhile the coefficient of performance increase more than 74% on increasing the refrigeration temperature from Tc = 8 °C to Tc = 15 °C. Then, the performance of ERS is obtained at the subcritical conditions at varying generator temperatures. At subcritical mode, COP is found to be directly proportional to the generator temperature, and the highest COP occurs at an optimum generator temperature. The performance of the ERS with various refrigerants as R717, R718, R245fa, R123, R141b, and R365fa is calculated at the critical mode. With refrigerant R717, the system shows higher performance as well as a cooling effect than other refrigerants. However, most environmental benign refrigerant R718 shows comparatively low performance, but it is found that R718 produces a significant cooling effect than other refrigerants excluding R717 refrigerant.

An experimental investigation to determine the optimal heat source temperature for R141b ejector operation in refrigeration cycle

This paper provides an experimental investigation of an R141b ejector refrigeration system which concentrates on the effect of the driving generator temperature on the ejector performance under various working conditions. The experimental ejector refrigerator working with R141b was designed and built for investigation. The generator temperature was varied to determine the optimal generator temperature. The working generator temperature was varied between 80 and 105 °C. The evaporator temperature was ranged from 6 to 14 °C. Three primary nozzles were used to investigate the effect of the ejector area ratio to the optimal performance. The condenser saturation temperature was ranged from 28 to 34 °C. It was found that the optimal generator temperature varied with the change in the working conditions and primary nozzle used. With variation in the evaporator temperature, the upstream pressure ratio was initially introduced and its impact on the optimal operation was later discussed. This upstream pressure ratio strongly influenced the optimal operation at relatively high evaporator temperature, and hence, the proper value was determined for this present work. In addition, the proper ejector area ratio for working condition consistent with this present work was determined. The results also demonstrated the feasibility of using an ejector refrigerator with a relatively low generator temperature while rejecting unwanted heat at relatively high condensation temperature.

Performance investigation of a solar-driven ejector refrigeration cycle

Purpose This paper aims to investigate the performance and working fluids screening for an ejector refrigeration cycle (ERC) activated by solar energy. Several common and new hydrofluorocarbons, hydrocarbons, hydrofluoroolefins and hydrofluoroethers are proposed as refrigerants for the ERC to determine the most appropriate one. Design/methodology/approach The ejector performance is characterized by the ejector area ratio (EAR) and entrainment ratio (ω), while the cycle performance is described by the coefficient of performance (COP). The influences of many working parameters like the evaporator, condenser and generator temperatures on the ejector and cycle performances are investigated for all candidates as well. Findings The results indicate that the best ejector and cycle performances are attained with the highest critical temperature dry refrigerant, i.e. R601 under all studied working conditions. From the perspective of energy efficiency and environmental issues, R601 can be considered the most appropriate working fluid amongst all candidates. However, extra attention should be considered against its flammability. The maximum COP, the corresponding ω and the necessary EAR using R601 are 0.743, 1.02 and 15.5, respectively, with 25 ºC condenser temperature and the typical values for the rest operating conditions. Originality/value Many common and new hydrofluorocarbons, hydrocarbons, hydrofluoroolefins and hydrofluoroethers are suggested as working fluids for the ERC to determine the most appropriate one. The mixing process inside the ejector constant-area section is assumed constant-pressure process.

Experimental Investigation of Ejector-Assisted Vapor Compression System

The performance of an ejector as an expansion device rather than the conventional expansion valve or capillary tube in a vapor compression system is experimentally analyzed. Experiments have been conducted using 28 ejectors of different dimensions at the same condenser and evaporator temperatures, and it has been observed that for utmost performance, an optimum area ratio of the ejector is required. One of the ejector geometry has been experimented further for a wide range of condenser and evaporator temperatures. The coefficient of performance is found to be enhanced by at least 10% in comparison to the conventional vapor compression system for the considered range of condenser and evaporator temperatures and the maximum improvement in COP obtained is 12.83% at 14.3∘C evaporator temperature and 32.4∘C condenser temperature with 17.9211 ejector area ratio. The refrigerant R134a has been used as the working substance.