Ejector Performance Research Articles

A novel R744 multi-temperature cycle for refrigerated transport applications with low-temperature ejector: Experimental ejector characterization and thermodynamic cycle assessment

A novel vapor-compression system concept employing carbon dioxide as the refrigerant is proposed to serve the needs of a typical medium-size refrigerated truck used for multi-temperature (MT and LT) goods delivery. The system design is based on the implementation of an ejector as the only component increasing the refrigerant pressure from the LT evaporation pressure to the MT evaporation pressure, thus providing cooling effect at two different temperature levels with only one stage of compression. The ejector was experimentally tested and its ability to effectively entrain mass flow rate from low pressure suction conditions (corresponding to a LT evaporation temperature of −25 °C) was assessed. Lower external ambient temperatures and consequent lower expansion energy available at the ejector motive nozzle leads to a reduction of the maximum achievable pressure lift. Moreover, a significant degradation of the ejector performance towards the highest pressure lifts is experienced. Based on the ejector experimental data, a numerical evaluation of the proposed cooling unit performance has been performed, highlighting that in design conditions (LT evaporation at −25 °C) the cooling unit provides a LT freezing power ranging between 1.1 kW and 2.3 kW and a corresponding minimum MT cooling power ranging between 5.1 kW and 3.8 kW, depending on the chosen ejector lift. The MT cooling power can be further increased by increasing the compressor mass flow rate. The system COP is maximized at the maximum available lift provided by the ejector.

Investigation and development of improved methods for the design of ejector

The ejector is a simple mechanical device having no moving parts has the characteristics of being fixed, reliable, inexpensive, simple to keep up and handle. An ejector is a device that allows a fluid at low pressure flow (secondary fluid flow) by speed up some other fluid at high pressure flow (primary fluid flow) through nozzle. It is used in lot of industrial processes, particularly with air or steam as operating fluid. The ejector system has a vast range of applications. They reduce pollution compared to fossil fuel power plants. The geometry of the ejector has a remarkable impact on the performance of the ejector. A steam ejector can effectively make use of unused heat resources, which is mainly used in air conditioning, refrigeration, and seawater desalination sectors. The geometry of mixing chamber of the steam ejector features a critical effect on its outcome. The numerical simulation results shows that the entrainment ratio and critical back pressure of the steam ejector initially increases and then decreases with the increase in mixing chamber length for different mach numbers. Mixing chamber length of 40 mm to 80 mm and nozzle throat diameter 2.5 mm provides high performance of steam ejector for steam ejector refrigeration.Ejector with converging-area chamber has higher performance than ejector with constant area section. Hydrocarbon ejector cooling applications is highly recommended.

Experimental study of a R290 variable geometry ejector

Ejectors are classified as fluid-dynamics controlled devices where the “component-scale” performances are imposed by the local-scale fluid dynamic phenomena. For this reason, ejector performances (measured by the pressure-entrainment ratio coordinate of the critical point) are determined by the connection of operation conditions, working fluid and geometrical parameters. Given such a connection, variable geometry ejector represents a promising solution to increase the flexibility of ejector-based systems. The present study aims to extend knowledge on variable geometry systems, evaluating the local and global performances of the R290 ejector equipped with a spindle. The prototype ejector was installed at the R290 vapour compression test rig adapted and modified for the required experimental campaign. The test campaign considered global parameter measurements, such as the pressure and the temperature at inlets and outlet ports together with the mass flow rates at both inlet nozzles, and the local pressure drop measurements inside the ejector. In addition, the experimental data were gathered for different spindle positions starting from fully open position the spindle position limited by the mass flow rate inside the test rig with the step of 1.0 mm.

Numerical investigation of the effect of primary nozzle geometries on flow structure and ejector performance for optimal design

Numerical investigation of the effect of primary nozzle geometries on flow structure and ejector performance for optimal design

Performance of a two-stage ejector with varying liquid fraction at its inlet

Liquid volume fraction (LVF) in a two-phase flow has a certain effect on the flow performance. In this paper, a two-stage ejector applied to a multi-evaporator refrigeration system was proposed by the authors, in which, the refrigerant of R134a is used and then the effects of different LVF in the two-stage ejector inlet on the two-stage performance were studied by using CFD simulation, which is the novelty of this study. One of the main contributions is that the reason for the changed performance of each stage was explained by analyzing the volume flow rates, density and mass flow rates of the two-phase mixture when the LVF of one, two or three inlets varied. The results show that: (1) when the LVF of one inlet increases, the two-phase mass flow rate can be increased evidently due to the significant increase of the density of the mixture; (2) if one inlet fluid is in two-phase, the improvement of the LVF in the first-stage secondary flow, the performance of the first-stage as well as the second-stage can be improved; (3) if two inlet flows are in two-phase, the increase of the LVF of the two inlet flows of the first-stage with the same proportion can offer the best performance to both stages; and (4) when the LVF of three inlet flows increase from 0.04 to 0.12 with the same proportion, the ER of both stages can be increased evidently.

Vehicle refrigeration modification using an ejector: Optimization and exergoeconomic analysis

BackgroundAdvances in technology in recent years have increased energy consumption which has led to global warming. In line with the Paris agreement, the optimal use of energy is a way to overcome the issue. Air conditioning and refrigeration systems are among the sectors that account for a large share of energy consumption. This has elicited the implementation of optimization of refrigeration systems. MethodIn this research, the aim is to utilize the radiator waste heat of an engine with a volume of 2000 cc in an ejector refrigeration cycle as an alternative to conventional refrigeration cycles in vehicles. For this purpose, the ejector refrigeration cycle is modeled with energy, exergy, and eco-exergy equations and the ejector is modeled with dynamic gas equation. After modeling, effective parameters, namely, condenser outlet temperature, inlet temperature and pressure to the secondary nozzle, and inlet temperature to the primary nozzle are optimized using TOPSIS multi-objective optimization method. The selected objectives were reducing system capital investment cost, and increasing, COP, and the ejector performance (ω) criterion. ResultsIt was found that the ejector refrigeration cycle reduces the electric power and capital investment cost by 0.743 kW and 0.0028 $/h, respectively, and also increases the COP by 0.917 compared to the conventional refrigeration systems in the vehicle.

A comparative study of single and dual ejector concepts for anodic recirculation system in high-performance vehicular proton exchange membrane fuel cells

The fuel supply system is a critical element in Proton Exchange Membrane Fuel Cell (PEMFC). In vehicular applications, an anode recirculation system (ARS) is required to return residual hydrogen to the fuel line. A 1D model of an ejector-based ARS was created and integrated with a vehicular PEMFC in this study. Therefore, two configurations, single-ejector-based and dual-ejector-based ARS, were developed to regulate the fuel supply and, thus, utilized to examine and conduct a comparative study of their advantages and disadvantages to the dynamic behavior of the stack. The use of ARS was found to improve stack performance and fuel utilization by delivering high stoichiometry, recirculation rate, and relative humidity. Contrary to a single-ejector-based ARS, whose use is restricted due to its limited working range, dual-ejectors can cover all fuel cell stack operating ranges. Sensitivity analysis revealed that primary pressure was the most significant parameter affecting ejector performance and flow characteristics.

Optimization of geometric parameters of ejector for fuel cell system based on multi-objective optimization method

ABSTRACT In this study, the multi-objective orthogonal experiment is employed to optimize the geometric parameters of the ejector. The optimization objective is determined by applying linear weighting to the entrainment ratios for 100 SLPM and 990 SLPM operating conditions. Four geometric parameters are optimized, including the nozzle exit diameter, nozzle exit position, mixing chamber length, the mixing chamber diameter. Moreover, Computational Fluid Dynamics simulations are performed, and the effects of each geometric parameter and the interaction between parameters on the performance of the ejector are ranked by range analysis. The results show that the mixing chamber diameter has the most significant impact on the optimization objective, and the degree of influence of the other factors and interactions on the entrainment ratio varies for different operating conditions. Compared with the initial parameters, the parameters obtained by the multi-objective optimization method have an average improvement of 96% in entrainment ratio over the full operating range, and the experimental results are in general agreement with the simulation results. The adaptability analysis of the ejector performance indicates that the ejector optimized by the multi-objective optimization method can meet the hydrogen excess ratio requirements for the full operating range of the fuel cell system.

Study on the ejector-expansion refrigeration system for low-temperature freezer application: Experimental and exergetic assessments

In this study, the authors propose applying the ejector-expansion refrigeration system (ERS) to develop a -50 °C low-temperature freezer. The main performance of the ERS based prototype freezers were investigated by experimental and exegetic methods. The influences of nozzle throat diameter and compressor displacement on ejector performance were discussed in detail. The higher efficiency and transiting exergy efficiency of ejector could be obtained with a larger nozzle throat diameter and compressor displacement. When the nozzle throat diameter rises from 0.4 to 0.7, ejector efficiency and transiting exergy efficiency increase from 16.1% to 20.1% and 26.1% to 30.2%, respectively. Moreover, these results demonstrated that the ERS-based freezer could operate stably with appropriate nozzle throat diameter and compressor displacement. Compared with the conventional single-stage vapor compression refrigeration system (CVRS), the compression ratio of ERS was reduced by 15.8%. In addition, the system performance decreased with the increase of capillary tube length. When capillary tube length varied from 40 mm∼ 80 mm, the COP of the freezer decreased from 0.59 to 0.52, and the overall exergy efficiency of freezer decreased from 22.1% to 17.1%. This research confirms that the ERS could provide a novel way for developing a -50 °C low-temperature freezer.

Improving the performance of a commercial absorption cooling system by using ejector: A theoretical study

Absorption cooling systems (ACS) have lower coefficients of performance (COP) compared to direct expansion (DX) cooling systems. Nevertheless, ACS offers a green alternative to typical DX systems. In this study, a numerical model was developed for the commercial low-capacity Robur® absorption cooling system (RACS). The model was developed based on mass, concentration, and energy balance equations, in addition to heat transfer equations. The model results were validated against experimental data available in the literature for the same cooling unit yielding a good agreement. Hence, to improve the COP of the RACS, a vapor ejector was introduced between the generator and the condenser. An improvement of 70.6% in the COP was obtained at the design condition. A parametric analysis was implemented to study the significance of the key parameters in the RACS performance. It was found that the increase in the ambient temperature not only increased the activation temperature, but it also decreased the COP and increased the circulation ratio (CR). Consequently, in hot environments, lowering the evaporator temperature is recommended to avoid the need for higher CR. Optimizing the nozzle throat and the mixing tube diameter improves the ejector performance, and hence the RACS performance, as long as the ejector operates under critical conditions. Finally, the absorber coil was found to have the most significance on the RACS performance in comparison with the rectifier coil and the refrigerant heat exchanger.

Performance Evaluation and Degradation Mechanism for Proton Exchange Membrane Fuel Cell with Dual Exhaust Gas Recirculation

Fuel gas utilization and water management are particularly challenging integrated engineering problems in hydrogen–oxygen proton exchange membrane fuel cell (H2/O2 PEMFC) systems. Herein, a standardized process is adopted to evaluate the performance and investigate the degradation mechanisms of a PEMFC with dual exhaust gas recirculation. The purpose of incorporating recirculation subsystems in the fuel cell is to achieve a high fuel gas utilization rate and realize effective water management inside the stack, which consists of 3D‐printed ejectors and a customized recirculation pump. Evaluation of the electrochemical performance degradation and morphological characterization of the fuel cells under different operating strategies are performed after 50 h durability experiments. At a current density of 400 mA cm−2, the performance degradation rates of the stack decrease from 16.50% to 7.49% and 0.71% in the ejector and recirculation pump operation strategies, respectively. The results show that using exhaust gas recirculation devices (ejector/pump) in the fuel cell stack can help in effectively mitigating water flooding and chemical degradation of the membrane electrode assembly. The findings of the study provide a perspective on the exhaust gas recirculation behavior and contribute to the engineering application of H2/O2 PEMFCs.

New Adapted One-Dimensional Mathematical and Regression Model to Predict Ejector Performance

New Adapted One-Dimensional Mathematical and Regression Model to Predict Ejector Performance

Structural optimization of hydrogen recirculation ejector for proton exchange membrane fuel cells considering the boundary layer separation effect

Ejectors can greatly improve the efficiency of proton exchange membrane fuel cells (PEMFCs) by pumping unreacted hydrogen, and boundary layer separation (BLS) significantly impacts the recirculation performance of an ejector. However, current studies usually focus on improving ejector performance without considering the effect of the BLS. Therefore, this paper focuses on the influence of the key structural parameters of the ejector on the BLS and the recirculation performance of the ejector. A mathematical model of the hydrogen recirculation ejector is established. Considering the BLS effect, the influence of the ejector structure parameters on the BLS and the performance of the ejector are studied under the design condition. To ensure the high performance of the ejector in a wide working range, the structure of the ejector is optimized in the full working range. The results show that when the backpressure is less than the reflux point (3.47 bar), the ejector works in the subcritical mode, and the hydrogen recirculation ratio decreases rapidly with increasing backpressure. When the backpressure is 3.35 bar, the BLS appears, and the separation area increases with increasing backpressure. The optimized ejector has good hydrogen recirculation performance in a specific range of throat diameters (6.2–7.2 mm), constant-area mixing chamber lengths (26.8–33.5 mm), and nozzle exit positions (−8–2 mm). When the throat diameter is less than 13.4 mm or greater than 33.5 mm, the degree of BLS is intensified, and the recirculation performance of the ejector decreases sharply. When the primary flow pressure is 6 bar, the efficiency of the optimized hydrogen recirculation ejector is significantly improved by 33.2%.

Performance analysis of dual ejector-expansion air source heat pump cycle with three-stage evaporation for cold region application

In the present study, a modified dual ejector-expansion heat pump cycle with three-stage evaporation has been proposed for air source heat pump applications in cold region. This cycle layout could lead to an improvement in cycle performance due to much expansion work recovery and better temperature variation matching between cooled air and refrigerant. The performance analyses of the proposed cycle and ejectors using refrigerant R290 have been conducted at different operating conditions. In addition, the performance characteristics of the cycle are compared to those of the baseline cycles using a conventional expansion device, as well as a single ejector and a single evaporator. Through thermodynamic analyses, it is found that the improvements in the coefficient of performance of the proposed cycle can reach up to 26.1% and 10.5%, respectively, as compared to the basic vapor-compression heat hump cycle and ejector-expansion heat hump cycle. The exergy destruction of the proposed cycle can be reduced by 28.6% and 13.6% than those of the other two basic cycles. In addition, the performance of ejectors under different operating conditions is studied. The pressure lift ratio of the ejector in the new cycle varies from 1.36 to 1.69, which shows 14.3%∼21.6% improvement compared to the basic ejector-expansion heat pump cycle. Overall, this paper confirms the performance advantages of the proposed new heat pump cycle and its potential application in an air-source heat pump 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.

Experimental investigation on the performance of a novel resonance-assisted ejector under low pressurization

It is of great significance and value to apply different techniques to optimize the entrained performance of an ejector. In this paper, a novel resonance-assisted ejector is proposed by applying a mixing enhancement technique. Experimental studies were conducted to investigate the oscillation effect on the performance of the ejector under different geometries and operating conditions. The results show that adding high-frequency oscillations to the primary flow can provide up to a 14% improvement in entrainment performance. As the length of the resonance tube increases, the performance tends to increase and then decrease. The performance is sensitive to variations in the distance between the nozzle of the resonance generator and the inlet of the resonance tube. The shorter the distance, the greater the performance improvement. The critical pressure ratio of the resonance generator is approximately 5.5. The entrained performance enhancement rate increases gradually over the critical pressure ratio. Entrainment enhancement caused by resonance generator can be eliminated with small mixing cross-sectional areas. The oscillation effect enhances the entrained performance at different backpressures, and the higher the pressure the greater the enhancement rate. This paper provides new ideas for the optimization of ejector performance.

Multi-Objective Optimization of a Solar Combined Power Generation and Multi-Cooling System Using CO2 as a Refrigerant

This paper proposes a new combined multi-cooling and power generation system (CMCP) driven by solar energy. Carbon dioxide is used as a refrigerant. A parabolic trough collector (PTC) is employed to collect solar radiation and convert it into thermal energy. The system includes a supercritical CO2 power system for power production and an ejector refrigeration system with two ejectors to provide cooling at two different evaporating temperatures. The CMCP system is simulated hourly with weather conditions for Tunisia. The PTC mathematical model is used to calculate the heat transfer fluid outlet temperature and the performance of the CMCP system on a specific day of the year. A 1D model of an ejector with a constant area is adopted to evaluate the ejector performance. The system’s performance is evaluated by an energetic and exergetic analysis. The importance of the system’s components is determined by an exergoeconomic analysis. The system is modeled using MATLAB software. A genetic algorithm is used for multi-objective optimization to determine the best values and solutions for the system’s design parameters. The optimal energy and exergy efficiencies were found to be 13.7 percent and 37.55 percent, respectively, and the total product unit cost was 31.15 USD/GJ.

Simulation and experimental measurements of 10-kW PEMFC passive hydrogen recovery system

Simulations are performed to examine the performance of a vacuum ejector in the hydrogen recovery loop of a 10-kW PEMFC system. The simulations commence by examining the effects of the primary flow fluid pressure and secondary flow temperature on the recirculation ratio and hydrogen stoichiometric ratio. Further simulations are then performed to investigate the temperature, pressure, velocity and Mach number distributions within the ejector for various values of the primary flow inlet pressure and temperature. A prototype ejector is fabricated using a 3D printing technique. Experiments are performed to evaluate the gas tightness and gas recovery performance of the ejector under realistic operating conditions. The simulation results show that the recirculation ratio and hydrogen stoichiometric ratio increase with a decreasing primary flow inlet pressure and secondary flow inlet temperature. As the primary flow inlet pressure increases, the pressure, velocity, and Mach number in the mixing chamber increase, and the hydrogen recovery performance decreases. Furthermore, as the temperature of the primary fluid flow increases, the stability of the isentropic flow condition within the ejector is enhanced. The experimental results show that the prototype vacuum ejector has a maximum gas leakage of just 0.7 psi and a minimum hydrogen recirculation rate of 59.3%. Consequently, it has significant potential for passive hydrogen recovery in large-scale fuel cell systems.

Research on performance of multi-nozzle ejector for aeroengine air system

Research on performance of multi-nozzle ejector for aeroengine air system

Experimental performance of ejector heat pump operating in the sub-critical mode

Ejector heat pump (EHP) is an efficient-energy technology with a promising potential to replace the vapor compression cycle in heating and cooling applications. It can be powered by low-grade waste heat and uses environmentally friendly working fluids. EHP has also become a viable solution in research seeking cooling applications. However, little attention has been paid to using EHP for heating purposes. In order to investigate this, a steam EHP for domestic water heating was designed and built. The coefficient of performance (COP) is evaluated at various operating and design conditions in sub-critical operational modes to achieve higher condensation temperatures. Two primary nozzles with a throat diameter of 1.5 mm and 2.0 mm were investigated. The primary nozzle is movable along the ejector’s axis, allowing investigation of its positional effects on the EHP’s COP. Experimental measurements revealed that using a smaller throat diameter results in a high COP and low back pressure. The EHP COP and back pressure increase when the LTE temperature increases. Using a throat diameter of 1.5 mm, the EHP COP increases as the nozzle exit position (NXP) becomes closer to the constant area section. A COP of 2.42 and a back pressure of 4.28 kPa are achieved at a high-temperature evaporator (HTE) temperature of 130 °C and a low-temperature evaporator (LTE) temperature of 30 °C using a primary nozzle with 1.5 mm.