Ejector Efficiency Research Articles

Research on CO2 ejector component efficiencies by experiment measurement and distributed-parameter modeling

In this study we combine the experimental measurement data and the theoretical model of ejector to determine CO2 ejector component efficiencies including the motive nozzle, suction chamber, mixing section, diffuser as well as the total ejector efficiency. The ejector is modeled utilizing the distributed-parameter method, and the flow passage is divided into a number of elements and the governing equations are formulated based on the differential equation of mass, momentum and energy conservation. The efficiencies of ejector are investigated under different ejector geometric parameters and operational conditions, and the corresponding empirical correlations are established. Moreover, the correlations are incorporated into a transient model of transcritical CO2 ejector expansion refrigeration cycle (EERC) and the dynamic simulations is performed based on variable component efficiencies and fixed values. The motive nozzle, suction chamber, mixing section and diffuser efficiencies vary from 0.74 to 0.89, 0.86 to 0.96, 0.73 to 0.9 and 0.75 to 0.95 under the studied conditions, respectively. The response diversities of suction flow pressure and discharge pressure are obvious between the variable efficiencies and fixed efficiencies referring to the previous studies, while when the fixed value is determined by the presented correlations, their response differences are basically the same.

Investigation of the Overall Efficiency of Steam Jet Ejector over a Range of Working Conditions

A common use of steam ejector is a simple vacuum pumping. It has been shown many advantages, primarily the ejector is inexpensive, small, no moving parts to go wrong, and also the equipment has shown significant cost reduction in the operating stage over the mechanical pumps when the exhaust steam be put to an effective use. The present work addresses with the development of a steam jet ejector by studying the effect of nozzle geometry on the efficiency and performance of steam jet ejector. The main objective of this study is to assess the efficiency of steam ejector as pump and as feed heater with variable pressures and temperatures for different nozzle diameters used (2, 3, 4, 5, 6 mm). The system that has been built in the present work consists of boiler, feed water tank with feed pump, suction and delivery tank, and ejector. The results show that the efficiency of ejector as pump will increase, while the efficiency as a feed water heater decreases if the steam mass flow rate or steam pressure increases. Also, the ejector efficiency will rise up for smaller nozzle inlet diameter, and the best performance was obtained at 4.5 bar steam pressure.

Liquid Jet Ejector Efficiency Improvement

The issues of application of an agitator, a diffuser, and a vertical pipe in a liquid jet ejector are considered. Possible versions of an agitator as a rotating nozzle with blades are recommended. A physical and mathematical model based on fundamental equations, which reflect the operating process of the device, is developed. The estimated dependencies and restrictive conditions of operation of the electrically driven rotating nozzle and blades ejector are provided. The increase in the efficiency of application of the agitator, diffusor, and vertical pipe is numerically quantified by means of extreme characteristics. Thus, a maximum efficiency gain of 37% after agitator is installed; 13% when diffuser is installed; 5% when vertical pipe is installed can be reached. The characteristics that reflect the relationship of maximum attainable operating parameters and the corresponding values of optimum relative nozzle area are obtained. The constancy of the optimum relative nozzle area in a wide range of operating parameters, while using the agitator alongside the diffuser and the vertical pipe, is revealed. Hence, if the agitator is applied, the optimum relative nozzle area is 0.29 ... 0.30, if the diffusor and vertical pipe are added, then – 0.40 ... 0.41. The recommendations on the implementation of the obtained results are made.

Performance optimization of a transcritical CO2 refrigeration system using a controlled ejector

An on-line optimal quasi cascade controller for an ejector with variable nozzle throat area is proposed to improve the operating performance of the transcritical CO2 ejector refrigeration system. The optimal gas cooler pressure is tracked in real time by the controller including a tracker and a predictor. Using the system dynamic model, the dynamic responses of the system performance and ejector efficiency under variable nozzle throat area are first analyzed. Then the parameters of the tracker and predictor are determined by simulation respectively which exhibits a good dynamic characteristic with an acceptable settling time. Besides, the controller presents a good robustness under variable compressor speeds and mass flow rate of cooling water. Furthermore, the system performance is actually increased to the maximal value by the controller even at the variable operating conditions. Finally, the optimal controller is verified by experiments to be an effective way to improve the system performance automatically.

Performance analysis of a novel hybrid vapor injection cycle with subcooler and flash tank for air-source heat pumps

In this paper, a novel hybrid vapor injection cycle (HVIC) with subcooler and flash tank for air-source heat pumps is proposed. In the HVIC, an ejector is applied to realize the advantages of both the subcooler and flash tank vapor injection, which can efficiently reduce the irreversible thermodynamic loss and improve the system performance, especially at low ambient temperature conditions. The performance enhancement potential of HVIC is compared with conventional subcooler vapor injection cycle (SVIC) and flash tank vapor injection cycle (FTVC) using cycle simulations. The simulation results indicated that for the HVIC using R290 as refrigerant, the coefficient of performance (COP) and the volumetric heating capacity can be increased by 2.8–3.3% and 6.4–8.8% compared to the SVIC system, 1.1–2.0% and 3.2–6.0% compared to the FTVC system, respectively. In addition, improving the ejector efficiencies and adjusting the injection pressure could also enhance the performance of HVIC. Exergy analysis indicates that the total exergy destruction for the HVIC is lower than that of SVIC and FTVC due to the application of an ejector, and therefore resulting in higher exergy efficiency. Overall, the HVIC could be more effective to enhance heating capacity and system efficiency.

Shape optimisation of a two-phase ejector for CO2 refrigeration systems

The shape optimisation of four CO2 ejectors is presented in this study. The considered ejectors were originally designed for a multi-ejector supermarket CO2 refrigeration system. The objective function was formulated to consider the multiple operating regimes, where the goal of the optimisation was to maximise the device efficiency. Six geometrical parameters were considered in the optimisation procedure. The applied optimisation scheme was a combination of a genetic algorithm coupled with the effective and validated CFD tool, ejectorPL. The optimisation results showed that the ejector efficiency improved by 6%. The shape modification trends were similar for all of the considered ejectors. All of the shape modifications resulted in a smoother expansion inside the motive nozzle, less intense turbulence inside the mixing section and a more uniform velocity field inside the mixing section. The obtained results showed that the presented methodology can be effectively used for ejector design for numerous applications.

Advanced exergy analyses of an ejector expansion transcritical CO2 refrigeration system

This paper presents a thermodynamic investigation on an ejector expansion transcritical CO2 refrigeration system with advanced exergy analysis. By splitting the exergy destruction into endogenous/exogenous and unavoidable/avoidable parts, more valuable information of the interactions among the system components and the components improvement potential is provided. The results indicate that the compressor with largest avoidable endogenous exergy destruction possesses the highest priority of improvement, followed by the ejector, evaporator and gas cooler. The system exergy destruction is dominantly endogenous, and 43.44% of the total exergy destruction can be avoided by improving the system components. The evaporator has a serious impact on the exogenous exergy destruction within the compressor and ejector, and its own exergy destruction is entirely belongs to endogenous part. The effects of the discharge pressure, compressor efficiency and ejector efficiency on the system exergetic performance are discussed. There is an optimal discharge pressure with respect to the minimum endogenous exergy destruction in the compressor. Avoidable endogenous exergy destruction rates of the compressor and ejector are respectively reduced by 93.6% and 81.7% when the corresponding component efficiency varies from 0.5 to 0.9.

Performance of fixed geometry ejectors with a swirl motion installed in a multi-ejector module of a CO2 refrigeration system

This paper provides a performance comparison of fixed ejectors with and without swirl flow at the inlet of the motive and suction nozzles installed in a CO2 supermarket refrigeration system. The Coefficient of Performance (COP) of the multi-ejector-based refrigeration system is dependent on the design of this device. The literature suggests that one of the possible ejector efficiency improvements can be performed using a swirl generator at the inlet of the motive nozzle. Therefore, a swirl generator was simulated for different size CO2 ejectors under typical operating conditions in a supermarket and for a range of rotational speeds. To compare the potential of both solutions, the device performance was numerically simulated using a validated Homogeneous Equilibrium Model (HEM) model for the same transcritical parameters. A global efficiency was presented and discussed for both fixed ejector types.

Designing a hydrogen gas ejector for 5 kW stationary PEMFC system – CFD-modeling and experimental validation

Ejectors are durable and inexpensive equipment for realizing hydrogen recirculation in proton exchange membrane fuel cell (PEMFC) systems. In the present work, a hydrogen recirculation ejector targeted for high turndown ratio operation in a 5 kWe PEMFC system was designed, manufactured with 3D-printing, and characterized experimentally with both air and humid hydrogen.The ejector was modeled at the experimental conditions with computational fluid dynamics (CFD) assuming 2D axisymmetric flow and with three turbulence models. A systematic comparison of experimental and simulation results was conducted with humid hydrogen at conditions covering the entire operating map up to 6 bar gauge primary pressure. The simulation results deviate on average 60%–70% from the experimental results, the deviation being less pronounced at conditions relevant in PEMFC applications.The SST k-ω turbulence model was identified to agree best overall with the experimental data while the RNG and Realizable k-ε turbulence models were observed to accurately predict the position of maximum ejector efficiency. Hence, the SST k-ω model is more useful for predicting ejector performance while one of the two k-ε models should be adopted when optimizing ejector design.

Exergy Analysis of a Solar-Driven Dual Parallel-Connected Ejector Refrigeration System

Nowadays, developing solar cooling technologies, especially ejector refrigeration system, has become preferable to scientific researchers. Exergy analysis is a technique in which the basis of evaluation of thermodynamic losses follows the second law rather than the first law of thermodynamics. An experimental exergy analysis of a solar-driven dual parallel-connected ejector (DPE) refrigeration system was conducted using water as working fluid. Saturated steam with 2 bar and 120oC was provided by heat–pipe evacuated tube solar collector with an assistant of an electric heater. The saturated stream was used as a motive flow for the ejectors. The exergy destruction and exergetic efficiency of the main components of the DPE refrigeration system were determined and compared with those when using a single ejector (SE) under same operating conditions. It was found that the most irreversibilities of both systems occurred at the solar collector, electric boiler and ejectors, respectively. Also, the total irreversibility (Exergy destruction) of the system when using DPE was lower than using a SE. In additions, the exergetic efficiency of the ejector, evaporator, and overall system when using DPE were increased by 21%, 10%, and 27%, respectively. The system thermal ratio (STR) and coefficient of performance (COP) of the system using DPE compared with SE were increased by 20% and 23%, respectively.

Experimental investigation on two-phase driven ejector performance in a novel ejector enhanced refrigeration system

This paper presents an experimental investigation on two-phase driven ejector performance characteristics in a novel ejector enhanced refrigeration system (NERC). An experimental setup using refrigerant R600a is designed and built based on the NERC system. In the experimental setup, the ejector uses two-phase refrigerant coming from the high-temperature evaporator as the primary fluid. The experiments are carried out to examine the influences of the main operational and geometric parameters, including the primary fluid pressure, the secondary fluid pressure, the NXP and the nozzle throat diameter. The results show that the entrainment ratio, the pressure lift ratio and the overall ejector efficiency of the two-phase driven ejector are strongly affected by those parameters. Additionally, the effect of the quality of the two-phase primary fluid is also experimentally investigated. The meaningful results obtained here may serve as good guidelines for further improving the two-phase driven ejector performance and providing promising use of the two-phase driven ejector in the ejector-expansion technology.

Эффективность эжекционного охла- ждения наддувочного воздуха и особенности ее экспериментальной оценки

To increase the power and fuel economy of internal combustion engines is necessary to achieve high degrees of efficiency and perfection of design of major it systems. One way to increase capacity is turbocharged with intermediate cooling of charging air. Among the systems the intermediate cooling of charge air is the least studied system ejection cooling. In order to improve engine design analyzed the functional and design features of the ejection system, cooling of charge air in an internal combustion engine with a supercharger. These estimates compare the studied system with traditional systems-air cooling, are considered and proved the advantages of the proposed system. The detailed description of the device and principle of operation of a software system ejection cooling. Defined objectives and program of the pilot study and determining the efficiency of extraction system-air cooling. The scheme of installation for the experimental determination of the effectiveness of the proposed system-air cooling. Define the required parameters for the analysis of gas-dynamic phenomena in the system of suction jet cooling during the pilot study, matched with the necessary measuring and recording equipment. The effectiveness of the system ejection-type cooling is assessed by the complex of parameters: the coefficient of ejection, ejector efficiency and thermal efficiency of the cooler, depending on the mode of operation of the engine. The selected places of installation of sensors for measuring pressure, temperature and flow gas streams. The limits to measurements of the parameters for the selected sensors. The methodology and calculated dependences to the experimental evaluation of the efficiency of the ejector, the charge-air cooler and induction system cooling Nadu exhibition of the air in General. The stages of processing of obtained experimental data. Developed methodology and scheme of the setup allows to experimentally evaluate the effectiveness of the ejection system-air cooling and to determine with a reasonable degree of accuracy the best modes of the system.

エアバキュームクリーナーのエジェクター部形状が性能におよぼす影響

In this study, we investigated the effect of the angle of air supply θ and the air inlet position x on the ejector performance of air vacuum cleaner. First, as the effect of the angle of air supply, it was found that in the case of θ=16deg, the ejector efficiency increases approximately 23% in comparison with θ=8deg which was a basic form. It is because that in the case of θ=16deg, high speed flow supplied from inlet expands uniformly in the narrow flow passage. Next, as the effect of the air inlet position, it was found that the ejector efficiency increases in the case of x=20mm regardless of the angle of air supply, and it raises approximately 56% at θ=8deg for x=3mm in particular. It is because that in the case of x=20mm, high speed flow which meets main passage at upstream side can be sent to the narrow flow passage independent of the angle of air supply.

大流量比エジェクタ設計のためのCFDによる最適形状探査

Shape optimization of a traditional ejector with a high flow rate ratio of suction and driving is carried out with CFD in order to maximize the ejector efficiency. Three different commercial optimization algorithms are then evaluated: a genetic algorithm, a hybrid algorithm of global and local exploration, and a combined algorithm of hybrid and self-exploration. It turned out that the combined algorithm provided the best shape among the three algorithms with no more than 100 cases of CFD calculation.

CFD-based shape optimisation of a CO2 two-phase ejector mixing section

In this study, the geometry of a CO2 ejector mixing section was optimised. Two optimisation algorithms, a genetic algorithm (GA) and an evolutionary algorithm (EA), were used with a validated CFD model based on the homogeneous equilibrium model (HEM). The ejector was designed to increase the Coefficient of Performance (COP) of CO2 refrigeration systems used in supermarkets. Hence, the objective function (OF) for the optimisation was defined as the ejector efficiency for various refrigeration system loads, which determined the ejector operating conditions (OCs). The optimisation results showed a very strong relation between ejector performance and the mixer diameter. Similar results were obtained with both optimisation algorithms. In each case, the mixer diameter was nearly equal to that of the baseline; however, the length of the mixing section was greater in the optimal design. The ejector efficiency of the optimised design was as much as 2% higher than that of the baseline design.

A computational study about the types of entropy generation in three different R134a ejector mixing chambers

The purpose of this investigation is to study the efficiency of a R134a ejector operating with three different mixing chambers by means of a CFD based entropy generation analysis. With the aid of the differential equation for entropy, the local entropy generation is pursued. Using this method, the areas where the irreversibilities occur are identified and geometry improvements suggested. The novelty of the numerical procedure presented herein is that the bulk entropy generation is analysed by means of four sources related with viscous dissipation and heat transfer, divided in mean and fluctuating terms. Entropy generation within the boundary layer has also been considered. The latter has proved to be small, as well as the heat transfer contribution. The fluctuating viscous dissipation accounts for more than 75% of the added entropy, being its main sources the shear layer after the nozzle exit and the shock wave trains, independently of their position.

Evaluating ejector efficiency working under intermediate pressure of flash tank–absorption cooling cycle: Parametric study

Combining the ejector–flash tank with the single stage absorption cycle using NH3/H2O as the working fluid has shown potential improvement in the COP. In our previous work, ejector efficiency faced some limitation due to the presence of booster at refrigerant streamline side. Removing the booster from the refrigerant streamline side and allowing the secondary flow of the ejector to work only under the intermediate pressure of the flash tank could optimize the ejector efficiency. This study examines the effect of system parameters, such as an entrainment ratio (ω), pressure ratio (PR), circulation ratio (CR), and the effectiveness of heat exchangers on the thermal loads, the coefficients of performance (COPc, COP), and the efficiency ratio (η) at various operating temperatures of the components. The study also discussed the effect of the operating conditions of the proposed cycle components on the performance parameters and the CR value in details. Comparing the results between the proposed cycle and our previous work showed that the new arrangement of the refrigerant streamline side increases the energetic secondary flow and consequently improved ejector efficiency. Moreover, the results showed that the thermal loads decrement of the generator and the absorber with SHE effectiveness increment is about 38% for each; while the thermal loads increment of evaporator and absorber with RHE effectiveness increment is found 14.86%, and 8% respectively. The performance increase ratio at maximum heat exchanger effectiveness is found 60.7% for SHE and 14.86% for RHE. Overall, the proposed cycle is considered beneficial from the viewpoint of the first law of thermodynamics.

Development and performance mapping of a multi-ejector expansion work recovery pack for R744 vapour compression units

A multi-ejector expansion pack, intended as a substitute for a standard high-pressure electronic expansion valve (HPV), was designed, manufactured and experimentally investigated. Four different ejector cartridges were sized to enable a discrete opening characteristic with a binary profile for a parallel-compression R744 system. The system is rated for 70 kW at a 35 °C gas cooler outlet temperature and a −3 °C evaporation temperature. High values of ejector efficiency, exceeding 0.3 over a broad operation range, were recorded for all four of the cartridges tested under vapour compression conditions. The applicability of the multi-ejector pack as a main flashing device was verified experimentally. Similar profiles of the discharge pressure control error were recorded for both alternative options: expansion purely in the HPV vs. HPV-assisted expansion in the multi-ejector pack.

Conventional and advanced exergy analysis of an ejector refrigeration system

This paper presents a comprehensive investigation of an ejector refrigeration system using conventional and advanced exergy analysis. Splitting the exergy destruction within each system component into endogenous/exogenous and avoidable/unavoidable parts provides additional useful information and improves the quality of the exergy analysis. Detailed calculations of the exergy destruction parts are schematically illustrated. Conventional exergy analysis indicates that about half of the total exergy destruction is caused by the ejector and about one quarter occurs in the generator. The advanced exergy analysis reflects the strong interactions between system components. The ejector has the highest priority to be improved, followed by the condenser and then the generator. The temperature difference in the condenser has the largest influence on the exergy destruction compared to that in the generator and the evaporator, and the ejector efficiencies are also very crucial for the exergy destruction. The system performance can be largely enhanced through improvements of the ejector and the condenser as well as the generator.

Performance Prediction of Compressible Two-Phase Flow through Ejectors

The objective of present work is to investigate theoretically the performance of two-phase flow (gas-liquid) through ejectors. The numerical investigation is based on non-homogeneous, (liquid and vapor velocities are not equal), non-equilibrium (liquid and vapor temperatures are not equal),two-fluid model, (Eulerian-Eulerian), conservation equations governing steady, two–dimensional (axisymmetric), turbulent, compressible, and parabolic two-phase flow. These equations are namely continuity, momentum, and energy. These equations are solved iteratively using control volume method with Prandtl’s mixing length as a turbulence model. Mass and heat transfer between the liquid and vapor phases are considered. Wall function is used instead of using very fine grid near the wall. The coordinates system is converted to bodyfitted coordinates. Refrigerant 134a is used as a working fluid. The Modified Benedict-Webb-Rubin (MBWR) equation of state is used to represent compressibility. The presented model is validated against previously published data in literature. The validation showed reasonable agreement. Effects of changes in geometry and operating conditions on ejector performance are investigated. Moreover, effects of certain parameters on ejector efficiency are presented showing that, for maximum efficiency both geometrical and operational parameters must be carefully selected. Overall, the results lead to useful information for ejector optimum design and prediction of the ejector behavior and performance.