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Annular ejectors are widely used in aerospace and other applications, and their performance has a significant impact on the overall system. In this paper, the effects of main nozzle area ratio, contraction section angle and diffusion section angle on the performance of annular ejector are investigated by using computational fluid dynamics combined with one-factor experiments, on the basis of which the L 9 (3 3 ) orthogonal table is established to optimise the structure of main nozzle and to screen the main influencing factors. The results show that the flow field inside the annular ejector is extremely complex. The influence of the main nozzle area ratio on the performance of the annular ejector is very great, and the change of the area ratio will lead to the change of the position of the second excitation sequence as well as the Mach number at the outlet of the main nozzle. However, as with the results of the one-way analysis, the effect of the angle of the constriction section on the exit Mach number is negligible.

Steam ejector, as a heat pump, plays a key role in ejector refrigeration system which operates with water vapor as an available, economic and environmentally friendly refrigerant. In this research, supersonic steam flow through the ejector is simulated by CFD methods to investigate effects of ejector geometry on its performance. Basic design criteria are entrainment ratio (ER) and critical compression ratio so that the former affects COP of the refrigeration system and the latter changes the temperature at which condenser is operated. For more accurate design, we also investigate the effect of ejector geometry (non-dimensional parameters consist of D/L and d/D) on the entropy generation rate as a design criterion. In fact, increase in ER and COP and decrease in the entropy generation rate are desirable changes in the present work. Among all geometric parameters which affect the entropy generation, the diameter of the throat of the primary nozzle is more effective than the rest. Finally, the ejector geometry has been proposed that make improvement in the ejector ER and COP of the refrigeration cycle up to 32% and 38%, respectively, and reduction of 28% in total entropy generation rate.

With the increasingly serious energy and environmental problems, the R1234yf ejector refrigeration system (ERS) shows great development potential in the refrigeration industry due to its simplicity, low maintenance costs and environmentally friendly nature. However, poor ejector performance has always been the main bottleneck for system applications. In order to overcome this problem, this paper proposes a design method for R1234yf ejectors based on the gas dynamic method and optimizes the geometrical parameters including the area ratio (AR) and nozzle exit position (NXP) to improve its performance through the control variable optimization algorithms. Based on the validated simulation model, the results show that the entrainment ratio increases initially and then decreases with the increase in AR and NXP, respectively; the AR has a significant effect on the shock wave position in the mixing chamber and the NXP can directly influence the expansion state of motive fluid; the ejector performance increases by about 17% over the initial entrainment ratio by the control variable optimization algorithms. This work can guide the R1234yf ejector design and promote the development of the ERS with environmentally friendly working fluids.

In a modified ejector cooling system (MECS), the ejector is assisted by a jet pump that allows the MECS to operate at higher condenser pressure relative to that in a conventional ejector cooling system (ECS). The behavior of an MECS is analyzed herein for a new eco-friendly working fluid, R1234yf, and compared with the commonly used refrigerant R134a. Energy and exergy investigations are conducted for a fixed cooling capacity of 1 kW and fixed ejector exit pressure of 700 kPa. The coefficient of performance (COP) obtained in the modified system is 0.29, whereas for the conventional ejector cooling system it is only 0.03 under the same designed conditions. At a generator temperature between 82 and 94 °C, the heat load in the MECS varies between 2.5 and 3 kW whereas the ECS consumes 14–44 kW while operating both systems at the same condenser pressure. The pump work required in the MECS is found to be higher than in the ECS, and it is higher with R134a in both systems. The total irreversibility of the MECS is calculated as 1.023 kW and 0.93 kW for R134a and R1234yf, respectively, under the designed conditions. Increasing the ejector exit pressure is found to decrease the performance of the modified system.

This report aims to investigate different component efficiencies present in CRKEC based ejector model. This study calculates the efficiencies of component on-design and off-design condition. This study shows the effect of the inlet, secondary, and exit pressure on the efficiencies of the nozzle, mixing, diffuser and entrainment efficiency of supersonic ejector. The literature’s definitions of ejector component efficiencies are listed below. There is a discussion of how ejector shapes, operating circumstances, and working fluid properties affect ejector efficiency. Future studies on ejector efficiency, ideal design, and control of ejectors and ejector systems will benefit from this research. The literature’s definitions of ejector component efficiencies are listed below.

A proton exchange membrane fuel cell (PEMFC) system requires an adequate hydrogen supply and circulation to achieve its expected performance and operating life. An ejector-based hydrogen circulation system can reduce the operating and maintenance costs, noise, and parasitic power consumption by eliminating the recirculation pump. However, the ejector’s hydrogen entrainment capability, restricted by its geometric parameters and flow control variability, can only operate properly within a relatively narrow range of fuel cell output power. This research introduced the optimal design and operation control methods of a dual-ejector hydrogen supply/circulation system to support the full range of PEMFC system operations. The technique was demonstrated on a 70 kW PEMFC stack with an effective hydrogen entrainment ratio covering 8% to 100% of its output power. The optimal geometry design ensured each ejector covered a specific output power range with maximized entrainment capability. Furthermore, the optimal control of hydrogen flow and the two ejectors’ opening and closing times minimized the anode gas pressure fluctuation and reduced the potential harm to the PEMFC’s operation life. The optimizations were based on dedicated computational fluid dynamics (CFD) and system dynamics models and simulations. Bench tests of the resulting ejector-based hydrogen supply/circulation system verified the simulation and optimization results.

In the adjustable CO2 ejector refrigeration system, the needle of the ejector as the component for regulation has a great impact on the performance of the refrigeration system. This paper investigates the changes in the entrainment ratio resulting from the adjustment of the needle position when two different needles are used. The results show that the Transient and steady state changes in the entrainment ratio are the same when a round needle is used, while the tip needle has a large change. At the same time, the round needle has a larger entrainment ratio relative to the tip needle when the throat area is reduced by the same percentage. The use of a round needle improves performance and stability during transient changes. For the round needle, with the increase of throat area reduction, the pressure change in the mixing section is reduced, and the surge in the mixing section is also reduced to a certain extent.

The theoretical analysis for the absorption cooling system of the multi-ejectors flash tank has been investigated. In this research, the analysis of the energy balance is conducted to predict the possibility of improvement in the thermal loads components of the absorption cooling system with multi-ejectors -flash tank. The computer program of simulation has been used to assess the single, double and triple ejectors for the absorption cooling system performance by utilizing a solution of the water ammonia as a working liquid, which operated under stable conditions. The results indicate that the cycle with three ejectors has the lower generator and evaporator thermal loads than the other cycles. It is also showed that the generator load for a cycle using double ejectors is higher than other cycles, while the evaporator thermal load is found permanently less than the basic and single cycle and slightly higher than the cycle which has three ejectors. As well as the improvement in overall COPs of the combined cycle using double ejectors under different operating conditions is higher than that of the other combined cycles. It was found that the total COPs for the double ejector cycle are higher by ratios (9.2% and 5%) at higher and lower operation conditions, respectively, than the combined triple ejectors’ cycle.

Recent work on ejector performance enhancement indicates that more information on ejector internal flow structure is needed to have a clearer picture of factors and conditions affecting operation and performance of these devices. This paper relies on experimental studies and CFD simulations to identify flow structures occurring under typical ejector refrigeration conditions and primary nozzle geometry and position. Effects on parameter distributions and the resulting operation of the device are given particular attention. The CFD model used for this purpose was validated by using in-house data, generated from an experimental prototype and over a wide range of conditions. The experiments for the selected condition were predicted very satisfactorily by numerical model. The study then focused on the role of the primary nozzle geometry and the distance of the nozzle from the beginning of the mixing chamber (NXP), in locally shaping the flow structure and the related consequences on ejector operation. Simulations on NXP for given operating conditions have shown that an optimum value was always found, and slightly varied the operating conditions within the range considered. Primary nozzle shape changes in terms of outlet diameters for given upstream conditions directly affected the expansion level of the flow. The simulations showed that an optimum range of nozzle exit diameters could be found, for which ejector performance was highest. Moreover, under these conditions it was observed that pressure fluctuations inside the ejector were reduced.

Due to unique technical and economic features, ejectors are widely used in various industries, including the water desalination industry and mixing fluids. Therefore, improving the ejector's performance is of utmost importance. In the present research, the effects of changing the primary nozzle outlet position (NXP) and changing the diameter of the primary nozzle (dn) on parameters such as Mach number, static pressure, dynamic pressure, mass flow rate, and entrainment ratio have been investigated and simulated using computational fluid dynamics. The results showed that increasing the NXP caused an increase in the mass flow rate of the secondary fluid and, as a result, the entrainment ratio of the ejector and a decrease in the size of the core of the primary fluid jet. This leads to an increase in the effective surface, a push of the shock train toward the constant-diameter region, and an increase in the maximum static pressure at the beginning of the diffuser. With the increase in the dn of the primary fluid jet core, the secondary fluid flow rate, the ejector entrainment, and the maximum static pressure value at the beginning of the diffuser increased, and the shock train was pushed toward the constant-diameter region.