Ejector Performance Research Articles

Parametric study of low‐temperature solar‐assisted flash evaporation desalination systems using two‐phase water–steam ejector

AbstractThis study aims to investigate a two‐phase subsonic ejector added to a flash evaporation desalination system to increase the system productivity of distilled water. The flash evaporation was of low‐temperature condition that it could be powered by a flat and evacuated tube solar water heater. A parametric study of superheat degree (range 5°C–25°C), back pressure (range 10–30 kPa of absolute pressure), primary fluid flow rate (range 1–3 L/min), nozzle diameter (range 1–3 mm), and salinity concentration (range 0%–7%) were investigated to examine the system productivity and the ejector performance in terms of its entertainment ratio under different operating conditions. Results show that the inclusion of the ejector led to an average of 99% improvement in system productivity, primarily through the efficient secondary flow. Moreover, the effect of the studied parameter was more pronounced in the considered flash evaporation desalination system as it has two places where flash evaporation occurs, compared with the normal system where the flash evaporation occurs at one place. All in all, the application of the ejector could enhance the system's productivity significantly under different operating conditions.

Enhanced performance of two-stage ejector based on flow-field coupling effect in MED-TVC systems

Steam ejectors serve as prevalent flow devices in multi-effect distillation systems, collecting excess steam and energy to promote sustainable energy utilization. In contrast to traditional ejectors, two-stage ejectors exhibit superior pressurization and vacuum capacities. However, the flow-field coupling effect, which is closely related to the entrainment performance of the two-stage ejector, is rarely explored. In this study, the flow-field coupling effect of the two-stage ejectors is investigated, and two new strategies are proposed to optimize the ejector performance. A concept of two-stage choking and a design principle for a two-stage choking structure is proposed by analyzing the size matching between two stages based on the flow-field coupling effect. Based on the design principle, the optimal structure parameter can be obtained by evaluating the two-stage choking state. Subsequently, a dynamic pressure control criterion based on the flow-field coupling effect is proposed to improve the entrainment performance. The results show that the entrainment performance of the two-stage ejector based on this control criterion is increased by 29.31 % and 4.15 % respectively when the second-stage primary pressure is 300 kPa and 450 kPa. Moreover, simulation results demonstrate that the upper limit of the entrainment performance is determined by the second-stage primary flow pressure.

Experimental and numerical studies on the performance of a precooled supersonic ejector

Precooling the secondary flow enhances the performance of the supersonic ejector. However, reducing the temperature of the secondary flow without experiencing significant pressure loss presents a challenge, particularly when the secondary flow is at high temperature and negative pressure. In response to this challenge, an original design for a two-strut supersonic ejector incorporating a plate-fin precooler is developed. Experimental and numerical calculation methods are employed to analyze the system’s performance under various secondary flow conditions, including ambient air, precooled gas, and non-precooled gas. Moreover, the impact of the secondary flow, including total temperature and mass flow rate on the flow structure and mixing process of the supersonic ejector is analyzed. The results show that the shock waves, reflected shock waves and shock trains exist in the flow channel of supersonic ejector simultaneously. The shock waves intensity decreases with the rise of the total temperature and mass flow rate of the secondary flow. Moreover, this leads to the static pressure behind the nozzle changing from a ω−shape to a U-shape along the flow direction. Meanwhile, the precooler has minimal impact on the pressure loss of the secondary flow while achieving a remarkable pressure recovery coefficient of over 97% and a temperature drops of above 40%. Thus, precooling the secondary flow helps decrease the static pressure in the suction chamber, which results in a minimum 29% increase in compression ratio, enhancing the pumping capacity of supersonic ejector. The study also observed that the drop of secondary flow temperature leads to a lower velocity ratio between the secondary and primary flows, which is beneficial for their mixing process.

Evaluating and optimizing of steam ejector performance considering heterogeneous condensation using machine learning framework

In the context of global warming and pollution concerns, refrigeration systems have become pivotal in energy conversion system. Within this realm, ejector types that harness renewable energy resources emerge as promising alternatives, offering a pathway towards environmentally conscious and resilient energy practices. Under specific conditions, condensation within the heat exchanger results in diverse droplet sizes at the ejector inlet, inducing homogeneous-heterogeneous condensation (HMTC) and heterogeneous condensation (HTC) phenomena. This study aims to evaluate and improve the performance of steam ejectors by investigating and optimizing the effects of homogeneous condensation (HMC), HTC, HMTC, and evaporation processes using a machine learning (ML) framework. The drone squadron optimization (DSO), Particle Swarm Optimization (PSO), and Genetic Algorithm (GA) are chosen and used in the ML framework to find the optimal droplet radius and number. Findings predict that the presence of 1018 1/kg droplets with a radius of 0.02 μm (Optimal mode) at the inlet results in a 2.6 % increase in the entrainment ratio (Er) and a 6.9 % reduction in the entropy generation compared to the baseline mode. Generally, the research reveals that HTC exhibits superior performance compared to prevailing theories, leading to enhanced ejector performance.

Evaluasi Kinerja Steam Jet Ejector Tingkat Pertama Terhadap Kevakuman Kondensor

The steam jet ejector is a device for extracting NCG from the condenser. NCG can increase the pressure in the condenser until a vacuum condition is not reached. The diffuser pressure on the steam jet ejector has a normal operational limit of below 1 atm, meaning that the ejector performance will be optimal if it is operated at the operational limit under vacuum conditions. The expected objectives are to determine the effect of the steam jet ejector on condenser vacuum, calculate the performance of the first level steam jet ejector through pressure analysis in the diffuser section, calculate the performance of the steam jet ejector in actual conditions compared to the design data conditions and analyze actions that can be taken to improve the performance of the tool. Based on the results of calculations and analysis, it was found that the increase in steam jet ejector pressure had an effect on the increase in condenser pressure from the design pressure of 0.10 bar to 0.107-0.123 bar under actual conditions. The decrease in steam jet ejector performance results in the condenser vacuum level decreasing, but the equipment performance is within normal operational limit conditions, namely below 1 atm. The decrease in steam jet ejector performance is influenced by the motive steam mass flow rate, NCG mass flow towards suction, entrainment ratio value, NCG pressure and motive steam pressure which exceeds the design data.

CFD-based design algorithm for CO2 ejectors

In this work, a novel CFD-database generation algorithm for CO2 ejectors are presented. The algorithm is explained and its details discussed. A case for CFD database generation is then performed based on an ejector design for an industry client. The ejector design is investigated with different design parameters around the suggested design. Design improvements are suggested based on the numerical results, and a final design is suggested. The final design had a high ejector efficiency of simulated to be 46% at the design point, and the ejector performance is evaluated and discussed for off-design conditions.

Theoretical studies on wide-operating-range ejector based on operating conditions and multi-parameter coupling effect in proton exchange membrane fuel cell system

When the ejector in a fuel cell system operates under off-design conditions, its performance will significantly decrease. To improve the performance of the ejector under all operating conditions, this paper proposes a theoretical model for predicting performance and optimizing the structure of the ejector that has not been studied before. Based on the jet theory, a two-dimensional three-segment velocity distribution is established, and the exponent of the velocity function is modified by simulation and experimental data, reducing the model’s calculation error from 15% to 6.5%. By combining the Lagrange algorithm, we investigate the influence of operating conditions and multi-parameter coupling effects on ejector performance, obtaining optimal values for structural parameters under different load conditions. The results show that the optimal value of main nozzle exit position (Lx) increases with increasing current and the optimal value ranges from 0.5 to 6 mm. The influence of dimensionless parameter (λc), dimensionless parameter (λd) and diffusion angle (αd) on ejector performance is significant and optimal values exist. Reducing the nozzle throat diameter (dnt) can effectively promote the entrainment performance at low power, and four adjustment conditions are proposed. When dnt decreases from 3.2 to 2.0 mm, the operating range of the current is increased by 38.42%, the power range is increased by 42.12%, and the pressure drop of the ejector (pd) decreased by 9.66 bar. The theoretical model not only improves the accuracy of predicting the entrainment ratio, but also realizes the study of the influence of multi-structural parameter coupling effect on the performance of the ejector, which leads to a significant improvement in the optimization accuracy and efficiency, and extends the applicable power range of the ejector. This provides a new direction for the future performance optimization of wide operating range ejectors considering multi-parameter coupling effects.

Numerical study of a CO2 swirl ejector with lubricating oil

At present, most simulations of ejectors ignore the presence of lubricating oil, which may affect the accuracy of the results. Additionally, there has been less research conducted on the influence of motive nozzles with swirl generators on the performance of ejectors. In this study, a heterogeneous mixture model was developed for a three-phase swirl ejector equipped with a motive nozzle featuring a swirl generator. This article examines the performance of swirl ejectors under supercritical conditions using three-dimensional numerical simulations conducted in ANSYS. The study explores swirl ejectors with varying helical angles of 77°, 64°, 58°, 50°, 37° . The study also takes into account the influence of lubricating oil to enhance the practicality of the research. Firstly, lubricating oil with a volume fraction of 2 % was introduced into both the motive and suction streams, followed by conducting an ejection analysis. The results indicate that the swirl enhances the entrainment ratio, and the swirl strength can be modified by changing the helical angle. A smaller helical angle results in greater swirl strength and a higher entrainment ratio. When the helical angle is 37° and the helical pitch is 20 mm, a swirl number of 0.42, an entrainment ratio of 0.998, and an effective entrainment ratio of 0.863 is achieved. However, when the oil circulation ratio in the suction stream is increased from 2 % to 10 % while keeping the oil circulation ratio of the motive stream constant, the entrainment ratio decreases.

Performance prediction and geometry optimization of ejector in PEMFC system using coupled CFD-BPNN and genetic algorithm

The ejector is a promising hydrogen recirculation device in proton exchange membrane fuel cell (PEMFC) systems. However, the limited entrainment performance of the ejector at wide operating conditions hinders its development and widespread application in PEMFC systems. To address this challenge and design a high-performance ejector adapted to the wide power range of PEMFC systems, a backpropagation neural network (BPNN) model with computational fluid dynamics (CFD) simulation data is developed. The sensitivity analysis of geometric parameters based on the CFD model reveals that the nozzle throat diameter and the mixing chamber diameter exert the most pronounced impact on the entrainment performance, with average influence rates of 24% and 57%, respectively. Furthermore, two advanced multi-objective genetic algorithms are applied to improve ejector performance. The linear weighted genetic algorithm (LWGA) method proves effective in elevating the overall ejector performance, achieving a remarkable enhancement in entrainment performance of up to 7.9%. On the other hand, the non-dominated sorting genetic algorithm (NSGA- II) method is favorable for expanding the operational power range of the ejector by 30%, as well as a 4.5% increase in overall ejector performance. This work provides a robust framework for designing and optimizing high-performance ejectors in high-power PEMFC systems.

Optimization of the two-stage ejector with blocking area ratio of primary nozzle throat under certain liquid volume fraction in two-phase inlet fluids

This paper proposes an innovative two-stage ejector with a needle blocking the main nozzle area within 0%-60% to control the mass flow rate of the inlet. Based on this, under certain liquid volume fraction in two-phase inlet fluids, the nozzle exit positions (NXP1 and NXP2) and constant-area mixing chamber lengths (L1 and L2) of the first and second stages were optimized with blocking area ratio (BAR) of primary nozzle throat by using CFD simulation, the working fluid is R134a. The main results are as follows: (1) The maximum increase rate of the entrainment ratio (ER) of the first and the second-stage with optimization of four geometries without needle blockage are relatively slight, in comparison, both of them with optimization of L1 can reach 23.47% and 20.38%, which obtain the best improvement; (2) Under the condition of a needle blockage at the primary flow inlet of the first-stage ejector, the increase rate of ER1 with optimization of NXP1 and L1 are close to that without needle blockage; (3) Under the condition of a needle blockage at the primary flow inlet of the second-stage ejector, the first-stage ejector can achieve relatively large improvement of ER, especially, the optimization of NXP2 can increase the maximum ER1 by 258.73% of initial value, and the optimization of L2 can increase the maximum ER1 by 239.38% of initial value. The study in this work is helpful to understand the two-stage ejector performance improvement by adjusting the blocking area ratio of primary nozzle throat under certain liquid volume fraction in two-phase inlet fluids.

Numerical study on the influence of plugging rate on the performance of adjustable steam ejector

During the operation of thermal power plant systems, severe challenges to the quality and safety of the heat supply arise owing to the effects of peak regulation. Steam ejectors, widely employed in the district heating sector, often exhibit poorer performance under off-design conditions as a result of their fixed structure. This study analyzes the effects of varying plugging rate, primary pressure, and induced pressure on the performance of adjustable steam ejectors. As the plugging rate increases, the mass flow rate of the primary fluid decrease, potentially falling below 32%, and that of the induced fluid initially experiences a minor increase, followed by a rapid decrease. Concurrently, the critical back pressure also decreases with an increase in the plugging rate, potentially falling by up to 65%. By contrast, the entrainment ratio surges with increasing plugging rate, with the maximum increase reaching up to 4.75 times. Under the same primary steam pressure and induced steam pressure, there exists an optimal entrainment ratio. Furthermore, both the critical back pressure and the optimal entrainment ratio increase as the primary steam pressure and induced steam pressure increase.

Experimental and simulation analysis of the performance of premixed vertical ejectors

Infrared gas stoves have advantages such as rapid combustion speed and high thermal efficiency. The ejector, a pivotal component of the infrared gas stove, plays a crucial role in influencing the mixing ratio of gas and air. The vertical ejector is modeled and the simulation method is validated through experiments. The impact of structural parameters on the vertical ejector performance is investigated in this paper, like the contraction tube length, inlet diameter, and mixing tube length. The simulation results indicate that with the change in the contraction tube length, the excess air coefficient peaks at approximately 1.16. An increase in mixing tube length leads to a decreasing trend in the excess air coefficient. For ejectors with throat diameters of 9.8 mm, 11.2 mm, and 12.6 mm, their excess air coefficient reaches peak values at diffusion angles of 3.5°, 4.7°, and 5.0°, respectively. Furthermore, Response Surface Methodology is utilized to study the comprehensive influence of structural parameters on ejector performance and obtain the optimal structure. The excess air coefficient is 1.13 with the optimal geometric structure.

Numerical Investigation of a Two-Phase Ejector Operation Taking into Account Steam Condensation with the Presence of CO2

The application of a two-phase ejector allows for the mixing of liquid and gas and provides effective heat transfer between phases. The aim of the study is a numerical investigation of the performance of a water-driven, condensing two-phase ejector. The research was performed using CFD methods, which can provide an opportunity to analyze this complex phenomenon in 2D or 3D. The 2D axisymmetric model was developed using CFD software Siemens StarCCM+ 2022.1.1. The Reynolds-Averaged Navier–Stokes (RANS) approach with the Realisable k-ε turbulence model was applied. The multiphase flow was calculated using the mixture model. The boiling/condensation model, where the condensation rate is limited by thermal diffusion, was applied to take into account direct contact condensation. Based on the mass balance calculations and developed pressure and steam volume fraction distributions, the ejector performance was analyzed for various boundary conditions. The influence of the suction pressure (range between 0.812 and 0.90) and the steam mass flow rate (range between 10 g/s and 25 g/s) is presented to investigate the steam condensation phenomenon inside the ejector condenser. The provided mixture of inert gas (CO2) with steam (H2O) in the ejector condenser was investigated also. The weakening of the steam condensation process by adding CO2 gas was observed, but it is still possible to achieve effective condensation despite the presence of inert gas.

Effect of generator temperature on steam ejector performance in renewable refrigeration cycle considering wet steam model and dry steam model

The rise in global warming has led to an increased utilization of cooling systems. High energy consumption associated with common refrigeration cycles not only contributes to air pollution but also intensifies the consumption of fossil fuels. Consequently, the imperative to conserve energy has become paramount in today's world. One of the methods to decrease energy consumption involves employing systems capable of harnessing waste heat from industries, solar energy, and other sources. The ejector refrigeration cycle (ERC) stands as an example of such systems. In present study, the impact of elevating the generator temperature on various aspects such as flow behavior in the ejector, aerodynamic shocks, entrainment ratio (ER), and entropy production was examined. The investigation encompassed both wet steam model (WSM) and dry steam model (DSM). Based on the findings, it was observed that with an increase in generator temperature, the ER decreases while the production entropy increases. In the WSM, the liquid mass fraction (LMF) also experiences an increase. Additionally, the Mach number distribution in the DSM surpasses that of the WSM and the temperature drop in the DSM is greater compared to the WSM. With the rise in generator temperature from 388 K to 418 K, both the DSM and WSM exhibit a decrease in ER by 52.9% and 58.7%, respectively. Furthermore, the production entropy experiences a substantial increase of 180% and 206% for the DSM and WSM, respectively.

Study on the effect of pulsed gas flow on the entrainment performance of hydrogen ejector

The ejector is a crucial component of the hydrogen circulation system of proton exchange membrane fuel cell (PEMFC), which is widely used because of its simple structure, reliable operation, and no additional power consumption. However, the current research on pulsed ejectors is still lacking and in-depth. In this study, CFD modeling is conducted on the ejector, and the pulsed gas flow is simulated by user define function (UDF), and the influence of the pulsed gas flow on the entrainment performance of the ejector is analyzed. The results show that, compared with the steady-state condition, the entrainment performance of the ejector using pulsed gas flow under different primary flow pressures is improved, and the maximum entrainment ratio is 3.195 under steady-state conditions and 3.507 under transient conditions, which is increased by 9.8%. The effect is especially pronounced at low pressure, where the entrainment ratio increases by 16.6%. And by comparing the gas flow of different pulse frequencies, it is found that when the pulse frequency is 1Hz, the ejector has the best entrainment performance.

A comprehensive investigation of two-phase flow in off-design operating condition of ejector performance by using entropy generation analysis

A comprehensive investigation of two-phase flow in off-design operating condition of ejector performance by using entropy generation analysis

Experimental investigation of multi-ejector CO2 heat pump system with and without IHX

Environmental degradation due to the use of synthetic refrigerants should motivate end users to request natural refrigerants to secure their businesses from unforeseen negative ecological impacts. Further, using natural refrigerants as working fluids for HVAC requirements helps achieve zero CO2 emissions from this sector. The CO2 heat pumps are energy efficient units providing simultaneous heating and cooling. Implementing performance enhancing components like ejectors and/or internal heat exchangers (IHX) is sometimes beneficial. This study experimentally evaluates the ejector performance in a multi-ejector CO2 system of 33 kW cooling capacity, with and without an IHX, at different gas cooler exit temperatures. Evaporator and gas cooler exit temperatures are varied from 4 to 10 °C and 34 to 46 °C, respectively. These temperature ranges suit the simultaneous cooling (AC) and heating demands in various buildings and food- and beverage industries. At the gas cooler exit temperature of 42 °C, the system COP is improved by 12 % with an IHX, whereas the ejector efficiency increased from 14 to 18 % without the IHX. The ejector efficiency and entrainment ratio also increased at elevated heat rejection temperatures. However, as expected, the system COP decreased. Therefore, the heating system must be adapted to avoid high gas cooler exit temperatures.

Numerical investigation in effects of refrigerants’ thermodynamic properties on performance of supersonic ejector

ABSTRACT Using zeotropic mixtures with unique temperature glide characteristics as the working medium in heat-driven ejector refrigeration system will potentially reduce the irreversible losses in heat exchange process. However, the intrinsic link between the pure/mixture refrigerants’ thermophysical properties and the entrainment performance of supersonic ejector has not yet been elucidated. In this study, a novel ejector CFD model is established by coupling the real-gas thermodynamic equation and species transport equation, then the relationships between thermophysical properties of pure/mixture refrigerants and ejector’s dimensionless operational parameters were thoroughly investigated. The results indicated that the ejector expansion ratio rises as primary flow inlet temperature or refrigerant’s normal boiling point increases, while the dimensionless parameters of primary nozzle are relatively insensitive to the variation of primary flow inlet temperature and refrigerant’s boiling point, resulted in changes of supersonic jet expansion behaviour. Moreover, the specific volume and adiabatic index change characteristics resulted in minor fluctuations of primary nozzle’s dimensionless parameters. When the bubble point temperature is fixed at 30℃ in the condenser, the saturated vapor/liquid phase pressure glide characteristics of R600a/R1234ze mixture may lead to an increasement of ejector’s compression ratio.

Comparison of the performance enhancement of vacuum ejector by means of structure optimization and bypass methods

The ejector can create a vacuum environment without electricity and produce no pollutants, making it widely used in various fields. However, during the working process, a large amount of high-pressure air needs to be continuously supplied to maintain the vacuum level. Given the current energy shortages, it is essential to enhance the entrainment capacity and reduce the energy requirements of the vacuum ejector. To achieve this goal, a two-stage vacuum ejector (TSVE) and structure optimization are adopted. While achieving the same vacuum level (80 kPa or 90 kPa), the air consumption (m˙p) and entrainment ratio (Er) of vacuum ejectors with various shapes are compared. Through structural optimization, five high-performance vacuum ejectors (Pp < 0.6 MPa, Er > 0.65) are selected. Computational Fluid Dynamics (CFD) is applied to observe the mixing processes in the vacuum ejector. In addition, the optimized vacuum ejector and TSVE are compared to the original one. An experimental system is designed for this purpose. The findings indicate that both methods can enhance the performance of the vacuum ejector. However, the benefits of TSVE are more pronounced at lower vacuum levels, while the advantages of the optimized vacuum ejector become more obvious as the vacuum level increases.

Performance investigation of solar ejector cooling system: Case study area-Addis Ababa, Ethiopia

This study investigates the performance of a solar ejector cooling system under both on-design and off-design operating conditions, focusing on the case study area of Addis Ababa, Ethiopia. Data crucial to the analysis were gathered from the Ethiopian National Meteorology Agency (ENMA) over six consecutive years (2013-2018). The system's performance was evaluated through hourly and monthly analyses under on-design conditions, yielding promising results. Under on-design conditions, the system demonstrated favorable performance metrics. Specifically, at noontime in March, when the design points were set at Tg = 90°C, Tc = 30°C, and Te= 12°C, the system achieved a total hourly maximum coefficient of performance (COP) of 0.2049 and a cooling capacity of 186.9 W/m². Furthermore, the study determined that a collector area of 22.3 m² per ton of cooling capacity is required during noontime for all cooling seasons in Addis Ababa, Ethiopia. Additionally, an off-design operating condition map was developed for the system. The findings indicate that the solar ejector cooling system can effectively provide cooling during office hours (8:00-15:00) in Addis Ababa, Ethiopia.