Ejector Flow Research Articles

Energy-Saving Individual Heating Systems Based on Liquid-Vapor Ejector

The problem of increasing the efficiency of individual heating systems is solved by using heat pumps based on a liquid-vapor ejector with the working fluid R718 (water). The research object was the working process of the liquid-vapor ejector, based on the principle of jet thermal compression. It involves the generation of vapor in the nozzle of the motive flow of the liquid-vapor ejector and does not require its supply from an external source. Schemes and descriptions of the traditional system and the proposed scheme were given. Their difference from the traditional ones was indicated according to the schematic solution and working cycle. The article compared the proposed schemes’ thermodynamic calculation with the working flow R718 and traditional heat pump systems with carried-out refrigerants R134a, R410a, and R32. As a result, the values of the thermodynamic parameters of all system components were obtained. The coefficients of performance (COP) for the traditional and proposed cycles were determined. Applying the new scheme made it possible to increase the COP by an average of 40 %. An exergy analysis assessed the expediency of implementing vacuum units based on liquid-vapor ejectors in individual heating systems. This made it possible to compare systems that use several types of energy (e.g., electrical, thermal) and to determine their efficiency with high accuracy. As a result of the exergy analysis, the value of the proposed scheme’s exergy efficiency was obtained.

Modelling, Optimization, and Experimental Studies of Refrigeration CO2 Ejectors: A Review

CO2 is regarded as an effective and environmentally friendly refrigerant. Using a CO2 ejector is a proven method for enhancing the effectiveness of a transcritical CO2 refrigerant system. However, the complex internal flow of a CO2 ejector, involving supersonic effects, phase change effects, metastable effects, and so on, makes it difficult to understand. In order to summarize the current state of the technology and knowledge gaps, this work provides a comprehensive literature review on CO2 ejectors. In the first part, mathematical modelling and simulation calculations of CO2 ejectors are presented, and an overview and classification of ejector models are given. In the second part, the structural optimization part of the ejector is described in detail, and the nozzle structure, the mixing chamber length, improvements to multi-jet systems, and the impact of these factors on the system performance are analyzed. In the third part, flow visualization is used to study the complex flow phenomenon, and the effect of the shock wave on the entrained rate of the ejector is discussed. Finally, the paper outlines the relationship between all ejector technologies, working fluids, and ejector performance and makes valid recommendations for further research and development of CO2 ejectors.

Multi-Factor Design for a Vacuum Ejector Improvement by In-Depth Analysis of Construction Parameters

A vacuum supersonic ejector is an indispensable pneumatic device placed in nearly all industrial production lines. This device, also called a zero-secondary flow ejector, is characterized by the maximum entrained flow and the minimum secondary pressure. Numerical simulations were carried out by means of the CFD toolbox OpenFOAM v8 and its solver HiSA, which uses the AUSM+up upwind scheme. A single-factor analysis of eight parameters was performed to find how the ejector’s performance was enhanced or decreased, while other parameters were fixed. Four parameters were subject to further analysis to find the geometry that improves the standalone performance of the ejector. The mixing chamber length is the parameter that most improves its performance; alone it leads to a 10% improvement. A multi-factor analysis, based on a fractional factorial design, is carried out with the four relevant parameters. Results indicate that the multi-factor analysis enhances the performance of the ejector by 10.4% and the mixing chamber length is the factor that most influences the improvement. Although a multi-factor design improves the performance, no significant relevance has been detected with respect to the mixing chamber length improvement alone. The improved performance of this device leads to a reduction in operating time and, as a consequence, results in significant energy savings.

An improved hydraulic model of gathering pipeline network integrating pressure-exchange ejector

Pressure-exchange ejector is a novel equipment to overcome the pressure mismatch in multi-pressure gathering pipeline network. Hydraulic simulation plays an important role in the safety monitoring and operation optimization of gathering pipeline network. However, there is currently no hydraulic simulation model of the gathering pipeline network with the pressure-exchange ejector. This paper proposes a steady-state hydraulic simulation model, which consists of pipeline network structure sub-model, pipeline flow sub-model, and pressure-exchange ejector sub-model. Pipe flow, mass balance and detailed characteristics of pressure-exchange ejector are taken into consideration in the model to determine the unknown pressure and flow parameters. The proposed model is solved by the Newton-Raphson iterative method and validated by experimental and field data. The installation schemes of pressure-ejector in a real-world gas field are determined by scenario analysis to improve gas field production. This study provides an analytical tool for multi-pressure gathering pipeline network and guidance for gas field production.

Research on inner flow and energy characteristics of air ejector for liquid-ring vacuum pump

To analyze the complex flow characteristics, and reveal the mechanisms of energy transfer and hydraulic loss of the liquid-ring pump ejector. The numerical simulation and experiment were applied to analyze the complex shock wave structure, vortex evolution characteristics in the ejector and its influence on hydraulic performance, which provides a novelty reference for the optimization design of the ejector. Furthermore, novelty is expressed in the performance analysis of the ejector based on the performance of its matching liquid-ring pump. The results show that the λ-shock wave and Mach disk are formed inside the nozzle under the action of supersonic jet, and the triple point is formed as the incident shock wave, the reflected shock wave and the Mach disk intersect. The shock wave, as it propagates, changes from Mach reflection to regular reflection, and meanwhile, the position of triple point moves from the initial Mach disk to the new Mach disk. With the interaction of shock wave and jet boundary layer, the shock train is formed in the core region of the jet. The pressure, density and Mach number are oscillatory distributed in the shock wave region. There is a relatively large velocity gradient between the high speed primary flow and the low speed secondary flow near the outlet of nozzle, which induces the formation of opposite rotating vortices in the shear layer of the cylinder. With the evolution of the vortex, the high speed jet transfers energy through the cylindrical shear layer and is accompanied by the large hydraulic loss. The total entropy production of the ejector increases with the increase of primary flow pressure. The entropy production rate has a strong correlation with the vorticity magnitude.

Strategy to Apply DNS in a Supersonic Ejector

Being 20% of the building's total energy consumption, air conditioning can be a key to reduce significantly the energy demand and environmental impact. The blame lies in the compressor. The ejector is a simple equipment with zero energy consumption, ideal to assist the mechanical compressor. However, the ejector flow domain is complex and difficult to compute, once that is highly turbulent. The ordinary turbulence models are based on Reynolds Averaged Navier-Stokes, however, they cannot accurately compute the turbulence behavior inside the ejector. The optimal way to reproduce the interior flow is DNS, nonetheless, the computational cost is the major problem. This paper proposes two possible solutions to make DNS possible nowadays.

Experimental investigation of R744 transcritical flow and mixing in the two-phase ejector

In this work, the laboratory test rig for visualisation of the CO2 ejector is shortly presented. The internal flow structures in the premixing chamber and expansion cone are visualised using two different measurement arrangements, i.e. Particle Image Velocimetry (PIV) system and high-speed camera system. Both systems allow to determine some characteristic features of the R744 flows and propose some important quantities (i.e. expansion and mixing angles) describing expansion and mixing processes. Potentials of those preliminary results for field validation data are also pointed out.

Performance enhancement in a H2/O2 PEMFC with dual-ejector recirculation

Water management in various components of the proton exchange membrane fuel cell (PEMFC) is a significant and challenging issue affecting output performance. PEMFC utilizing dual ejector-based recirculation has been developed to evaluate and improve the performance and water transport properties. A detailed investigation into the effects of ejector operating conditions, such as primary flow pressure and secondary flow relative humidity, on the performance of PEMFC is conducted. The results show that significant performance improvement of PEMFC can be achieved by increasing the operating pressure. The power density can be increased by 37.8% and 86.5% with ejector primary flow pressures of 300 and 400 kPa, respectively. Furthermore, an optimization strategy integrating PEMFC operating condition is proposed to ensure the stability and lifespan of performance. The water management and integration optimization strategy obtained in this paper can provide valuable insight into options for improving the performance of PEMFC with dead-ended anode and cathode. • A multi-phase simulation of PEMFC with dual ejector-based recirculation was studied. • Water flooding can be mitigated by adding an ejector in PEMFC recirculation system. • The power density at 0.7 V can be increased by 37.5% with the ejector. • An optimization strategy integrating PEMFC operating conditions was proposed.

Improving the Energy Efficiency of a Gas Compression System at a Compressor Station

For natural gas pumping via main gas line gas compressor units are used. During the gas compressor units’ operation, there are natural gas consumption as a fuel and for technological needs. To prevent the escape of gas from the internal cavity of the centrifugal compressor N-370-18-1 into machine room, the design considers a hydraulic seal “oil-gas”. The feature of centrifugal compressor with hydraulic seal “oil-gas” is the discharge of gas from the degassing chamber through a candle into the atmosphere. Rational use of wasted gas make it possible to gain a benefit by saving raw and reducing environmental charges. The gas discharged into the atmosphere is proposed to be used in the fuel gas system of the unit. This requires to bring gas parameters in particular pressure and temperature, to the required ones. The kinetic energy of the low-pressure (passive) gas directed from the gas separator to the candle can be increased by direct contact (mixing) with the high-pressure (active gas) flow in the gas-jet ejector. The complexity of the mathematical description of all processes occurring in ejectors with a three-dimensional flow, and the high cost of conducting experiments with gases other than air, make it cost-effective to use CFD (Computational fluid dynamics) modeling methods to study the processes of gas flow in ejectors. The article presents the gas flow modeling results of the gas flow in an ejector by the ANSYS Fluent software package.

Numerical modeling of droplets injection in the secondary flow of the wet steam ejector in the refrigeration cycle

Steam ejector plays a key role in the refrigeration system. The water has been used as a working fluid because water is more economical and non-toxic. The operating fluid often enters the evaporator as a water liquid and droplets evaporate by absorbing heat. Cooling load changing causes the vapor in the outlet of the evaporator to be accompanied by droplets. Therefore, there are droplets at the inlet of secondary nozzle and flow should be simulated as a wet steam flow with injection droplets at the secondary flow. In this paper, the effects of droplets injection at secondary flow have been investigated on the performance of the refrigeration cycle. For this purpose, the Eulerian-Eulerian method has been used and the results have been validated with experimental data. Six cases are considered with different wetness and number of droplets in the secondary flow. The results of case 6 show COP, T¯outlet, and ER decrease about 22.93%, 15.66%, and 22.93%, respectively. In addition, the steam accompanies by droplets at the outlet of ejector. Therefore, it is essential for designers and operators to model and consider the effects of the droplets on the wall erosion to optimize the wet steam ejector and refrigeration cycle performance.

Numerical investigation of additional gas supply angle influence on flow in jet mill ejector

The results of numerical simulation of the flow in the jet mill ejector which is equipped with an additional gas supply channel have been presented. The influence of the supply system parameters on the nature of the flow in the ejector accelerating tube has been investigated. A comparative analysis of the change in the flow structure in the ejector for different values of the additional gas flow angle has been carried out. The dependences of the flow velocity at the outlet of the accelerating tube, the ejection coefficient and the thickness of the protective layer on the angle of the additional energy carrier supply have been scrutinized. The maximum values of the average output velocities for the given ranges of the additional flow parameters have been determined. Recommendations for the choice of geometric and gas-dynamic parameters of the additional gas flow to ensure the highest efficiency of the acceleration process in the jet mill ejector have been developed. The choice of the angle of the additional gas flow supply, which provides the highest average velocity at the outlet from the accelerating tube with the highest ejection coefficient, has been substantiated.

CFD modelling of the flow in zero-secondary flow ejectors: a sensitivity analysis to numerical parameters

This paper presents a sensitivity study of various CFD simulation parameters conducted in the case of a 2D axisymmetric ejector operating without induced flow. The influence of numerical parameters (solver, discretisation scheme, mesh and turbulence model) is investigated by comparing the various CFD results obtained (pressure, velocity, Mach number, and mass flow rate) with each other. The influence of the turbulence model is closely examined by comparing CFD results with the velocity measurements obtained by particle image velocimetry. The rules to be respected to achieve correct CFD simulation of the flow in supersonic ejectors are proposed. The use of the pressure-based coupled solver associated with the SST k-omega turbulence model is recommended. The terms of energy and pressure can be solved using first-order discretisation while the other equations (momentum, turbulent quantities) require second-order discretisation to correctly predict the supersonic flow with shocks.

R744 ejector simulation based on homogeneous equilibrium model and its application in trans-critical refrigeration system

The operational efficiency of the trans-critical R744 refrigeration system was analyzed from the perspectives of both the refrigeration system and the ejector components based on the refrigeration system thermodynamic and the ejector models. Considering the basic principle of the ejector and the homogeneous equilibrium model (HEM), the computational fluid dynamics software FLUENT was adopted to perform CFD simulations on the design of the R744 two-phase flow ejector. Further, the operational efficiency of a trans-critical R744 refrigeration system was analyzed from the perspectives of both the refrigeration system and the ejector components employing the refrigeration system thermodynamic and the ejector models. It was found that in the trans-critical mode, the power consumption of the R744 parallel compression trans-critical refrigeration system (EPR) with an ejector was always lower than that of the traditional R744 parallel compression trans-critical refrigeration system (BPR), and the maximum power consumption was reduced by 22.8%.

Numerical Study of Water-air Ejector using Mixture and Two-phase Models

In this research, steady-state Mixture and Eulerian-Eulerian method for liquid-gas parallel flow ejector were examined. The simulation demonstrated that the Mixture model simulation represents better and efficient. The Eulerian-Eulerian model needed longer computational time and had a complexity to achieve the optimal convergence. However, both methods' performances were shown slightly similar. The models indicated a difference of about 6% in the flow rate ratio, their pressure diagrams nearly coincide, and their velocity parameter varies by 7% by comparing to the existing experimental data. Additionally, the Mixture model results appropriately conformed much better to the experimental data. So, the Mixture model was chosen for futher parametric study. Simulation results indicated that the flow rate ratio decreases by increasing the throat's cross-sectional area, and the flow rate ratio increases by increasing the nozzle's cross-sectional area. In this regard, e.g., the flow rate ratio of ejector by increasing pressure from 70 to 80 kPa, the air inlet increases up to 94%, and by increasing ejector outlet pressure, the flow rate ratio reduces such that no suction can be observed at 160 kPa. Consequently, at 150 kPa pressure ratio, the flow rate ratio was reduced by almost 100%.

Study on evolution laws of two-phase choking flow and entrainment performance of steam ejector oriented towards MED-TVC desalination system

In this study, a visualizable experimental platform of steam ejector oriented towards MED-TVC desalination system is constructed, and the evolution laws of two-phase choking flow and ejector's entrainment performance under various operating parameters are obtained. Further, a matching double-choking theory with consideration of the condensing flow is developed to explain the inherent reason behind these evolution laws. Key results revealed that the formed two-phase choking flows have great effects on ejector's entrainment performance. The primary jet flow choking area linearly increases as the primary steam pressure raises, and the entrainment choking area experiences a small reduction, while the extended flow area marginally increases. Accordingly, the entrainment ratio significantly decreases, while the choking cross-section is slightly shifted upstream. In addition, the primary jet flow choking area considerably decreases with increasing entrainment pressure, but the entrainment choking area is nearly unchanged and the extended flow area increases by more than 8 times. As a result, the entrainment ratio remarkably increases, the choking cross-section migration distances are much larger than that in the case of primary steam pressure varies. A meaningful guide evolves from fact that priority should be given to restrain the condensing flow for achieving a higher energy efficiency of ejector.

Керування газо-масопотоками в струминному обладнанні

Based on a numerical simulation of gas flows in an ejector unit and an analysis of grinding chamber acoustic signals, this paper shows ways to increase the efficiency of jet grinding. To prevent ejector speed-up tube wear and to obtain a ground product without impurities, the effect of feeding an additional energy carrier flow on the flow pattern in the speed-up tube of a jet mill was studied. A comparative analysis of the ejector flow pattern as a function of the presence of an additional feed and the speed-up tube shape was carried out. It was shown that the use of a conical nozzle offers a more uniform flow at the ejector outlet. The additional energy carrier feed provides a uniform increase in flow speed and reduces speed-up tube wall wear. The acoustic signals of the mill working zones were related to the jet grinding process parameters, around which a ground product quality control method was developed. The paper presents a technique for determining the material particle size in the energy carrier flow from the results of acoustic monitoring of the process. The technique uses the established relationship between the dispersion of the acoustic signal characteristic frequency and the mass of the corresponding fracture of the mixture in in-flow material transportation. The technique speeds up material particle size determination and improves the finished product quality. An automatic system was developed to control the grinding process by controlling the loading process according to the characteristics of the grinding zone acoustic signals. An operating model of a controlled hopper of a gas jet mill was made. The operability of the control system was verified on a simulation model, which includes a control objet (mill) model and a control system model. It was shown that the system of mill loading automatic control by the characteristics of the grinding zone acoustic signals offers an up to 10 percent increase in mill capacity, which was verified in industrial conditions at Vilnohorsk Mining and Metallurgical Plant.

Computational fluid dynamic modelling of supersonic ejectors: comparison between 2D and 3D modelling

It is known that the global performances of ejector-based systems (viz., at the “global-scale”) depend on the local flow properties within the ejector (viz., at the “local-scale”). For this reason, reliable computational fluid-dynamics (CFD) approaches, to obtain a precise and an a-priori knowledge of the local flow phenomena, are of fundamental importance to support the deployment of innovative ejector-based systems. This communication contributes to the existing discussion by presenting a numerical study of the turbulent compressible flow in a supersonic ejector. In particular, this communication focuses on a precise knowledge gap: the comparison between 2D and 3D modelling approaches as well as density-based and pressure-based solvers. The different approaches have been compared and validated against literature data consisting in entrainment ratio and wall static pressure measurements. In conclusion, this paper is intended to provide guidelines for researchers dealing with the numerical simulation of ejectors.

Performance analysis of a modified dual-ejector and dual-evaporator transcritical CO2 refrigeration cycle for supermarket application

This paper proposes a modified dual-ejector and dual-evaporator transcritical CO2 refrigeration cycle for supermarket application. Based on the conventional dual-evaporator transcritical CO2 refrigeration cycle, the modified cycle introduces two ejectors and a flash tank. The first liquid-vapor ejector sucks partial throttling flash vapor flowing to the low-temperature evaporator into the high-temperature evaporator; the second vapor-vapor ejector takes the vapor from the high-temperature evaporator as the primary flow to entrain the vapor from the low-temperature evaporator, and then the compressor suction pressure is lifted. Furthermore, the introduction of the first ejector increases the primary flow of the second ejector, and then improves the ability of the second ejector to lift the suction pressure of the compressor. The performance comparison between the two cycles is conducted by adopting energy and exergy analysis methods, and the efficiencies of the two ejectors are also analyzed. The comparison results demonstrate that the use of dual-ejector reduces the compressor pressure ratio by up to 19.1% under a typical working condition, and the improvements of the COP and exergy efficiency could reach up to 15.9–27.1% and 15.5–27.5% under all given working conditions. In addition, the modified cycle has an optimal gas cooler pressure of around 8.15 MPa, which is lower than the 8.3 MPa of the conventional cycle. The performance comparison results state clearly the energy-saving potential of the modified cycle and its application prospect in supermarket refrigeration.

AN INVESTIGATION TURBULENCE MODEL OF STANDARD k- TO GET OPTIMUM PARAMETERS OF TURBULENCE CONSTANTS (cµ, c1, AND c2) OF COMPRESSIBLE FLUID DYNAMICS IN A CONFINED JET

This research aims to find the optimal standard k-e turbulence model constants (cµ, c1e, and c2e) for better predicting compressible fluid dynamics in an air jet ejector. The turbulence field in a jet flow plays an important role in influencing the performance of the momentum transfer process at a shear layer in nozzle application for momentum source and mixing process. In this research, some activities have been done before analyzing and optimizing the turbulence model constants, including preliminary turbulence modeling study for compressible flow in the air-jet ejector, verification, and validation with primary experimental data as well as by other secondary data. The preliminary studies in turbulence modeling presented that the turbulence modeling of a 3mm air jet-ejector resulted in a similar trend of the relation between entrainment ratio and motive fluid pressure. The results showed that the sensitive parameters in the standard k-emodel dissipation and diffusion terms, cµ, c1e, and c2e, strongly affected the optimum value of turbulence kinetic energy (k) and dissipation rate (e), compared to the reference model. Better k and e could be obtained by changing the c2e into positively proportional, but the cµ and c1e must be changed with opposite proportionality. It was found that the optimum standard k-e model constants in the case of air-jet ejector with 3 mm nozzle diameter for cµ, c1e, and c2e are 0.05, 1.48, and 1.88, respectively, with the error values for k being -8.88% and e being -17.44%.

Numerical investigation on the performance of transcritical CO2 two-phase ejector with a novel non-equilibrium CFD model

Flashing flow in the transcritical CO2 ejector was simulated using a novel non-equilibrium evaporation-cavitation CFD model. The novel model was verified using the experimental results of three ejectors with nozzle diverging angles (NDAs) of 0°, 2.00° and 6.70°. Furthermore, the effects of dimensions of mixing chamber and diffuser on the ejector performance were disclosed. The results suggested that prediction errors of secondary flow mass flow rate using the proposed model were less than 9%, and the maximum error of primary flow mass flow rate was within the range of 15%, which was much smaller than that of −34.55% predicted by homogenous equilibrium model. The results also showed that the mass transfer rates increased with increasing NDAs, and the maximum mass transfer rate of evaporation was approximately 3–13 times that of cavitation as the NDAs increased from 0° to 6.70°, proving evaporation dominates the flashing process in the CO2 ejector. Besides, the results showed that the entrainment ratio increased first and then decreased with increasing the mixing chamber width, mixing chamber length and diffuser angle, and the entrainment ratio was improved by 36.55%. This study is helpful to understand flashing mechanisms inside the CO2 ejector and improve the ejector performance.