Steam Ejector Performance Research Articles

Operation Rule of Steam Ejector and Influence Analysis of Ejection Position

In order to analyze the operation rule of steam ejector used in sewage treatment field, this paper established the mathematical model of steam ejector, simulated the internal flow state, analyzed the influence rule of external parameters on the performance of steam ejector, and analyzed the influence rule of ejector position on the water production ratio of steam ejector multi-effect evaporation desalination system. The research results show that under the same steam ejector structure, as the pressure of the working steam increases, the mixing and disturbance of the working steam and the ejected steam become more intense, and the diamond shock wave structure increases. As the pressure of the ejected steam increases, the momentum exchange effect of the shear blending of working steam and ejected steam is accelerated, and the speed increase rate becomes larger, and the diamond shock wave structure gradually gathers toward the nozzle. As the pressure rise of the ejected steam inlet and outlet increases, the backflow phenomenon near the wall in the mixing chamber becomes more serious, and the diamond shock wave structure is reduced. With the forward movement of the ejector position of the thermal steam compressor, the pressure of the ejected steam increases, and the water production ratio of the steam ejector multi-effect evaporation seawater desalination system shows a downward trend. Therefore, choosing appropriate working condition parameters can effectively improve the working performance of steam ejector and improve its operating efficiency in the field of sewage treatment.

Effect of water nano-droplet injection on steam ejector performance based on non-equilibrium spontaneous condensation: A droplet number study

Condensation and evaporation processes in high velocity flowing steam within ejectors profoundly influence the performance of these devices. In the current study, the effects of water droplet injection in the inlet of the primary nozzle on the condensation and evaporation processes are investigated through the wet steam model. The findings reveal that the existence of liquid droplets in the steam related to the inlet of the primary nozzle has effects on the two-phase parameters, shock waves intensity, entrainment ratio, mixing layer growth and two-phase heat, such that these parameters are minimized or maximized for a specific number of droplets. The inlet wetness in the primary nozzle provides a delay in the condensation shock, and the maximum delay happens in the wetness 0.4%. In the case of using 2.0×1017 droplets with 17.5 nm radius (wetness 0.4%), in comparison with the case of without the droplets at the inlet, the entrainment ratio, primary mass flow rate, and secondary mass flow rate reduce by 2.79%, 0.8%, and 3.72%, respectively. The novelty of this study is displaying the effects of water droplet injection in the inlet of the primary nozzle on the ejector performance.

Steam ejector performance considering phase transition for multi-effect distillation with thermal vapour compression (MED-TVC) desalination system

The multi-effect distillation with thermal vapour compression (MED-TVC) desalination system is efficient to produce freshwater. The steam ejector performance is not fully understood as the phase transition has been ignored in many studies. The present work develops a two-phase condensing flow model to assess the steam ejector performance considering nonequilibrium condensation phenomena. The transition of the flow structure from an under-expanded flow to an over-expanded flow in the steam ejector is investigated in detail. We present that the maximum Mach number can reach 4.02 in the under-expanded flow, which is weakened to 2.88 in the over-expanded flow. The steam undergoes several expansion-compression processes in the steam ejector in the under-expanded flow, which induces the formation and evaporation of massive droplets. In the over-expanded flow, the steam is compressed and then expanded after leaving the primary nozzle and the condensation process is not observed in mixing and constant sections. The increasing suction chamber pressure significantly improves the entrainment ratio while leading to an increasing entropy loss coefficient. The entrainment ratio is improved from 0.25 for the under-expanded flow to 1.69 for the over-expanded flow, while the entropy loss increases from 0.081 for the under-expanded flow to 0.29 for the over-expanded flow. This indicates that the transition of the flow structure from an under-expanded flow to an over-expanded flow can entrain more steam from the last effect while causes more entropy losses in a steam ejector for the MED-TVC desalination system.

Accurate condensing steam flow modeling in the ejector of the solar-driven refrigeration system

The ejectors are widely employed in power engineering installations, both refrigeration, and thermal ones. In the paper, a steam ejector of a solar-driven refrigeration system is investigated numerically, using different CFD models, to reveal the flow structures and evaluate its performance. A modified nucleation model adopting the Benson and Shuttleworth surface tension definition is proposed. The model composed by the modified nucleation model and Young's droplet growth equation demonstrates the superiority in predicting the non-equilibrium condensation phenomenon. An ejector experimental data is contrasted with three different numerical models, the results show that the effect of the non-equilibrium condensation (NEC) on the steam ejector performance cannot be ignored, and the modified model can accurately predict the ejector performance. An investigation of a steam ejector being a crucial part of a solar-driven refrigeration system is carried out employing different models. The internal flow structures and ejector performance are investigated, the difference of results predicted by three numerical models are compared and analyzed. The results show that the non-equilibrium condensation process reduces the entrainment ratio in critical mode, but it will enlarge the critical mode zone. Besides, the treatment of steam property has a certain impact on the calculation results.

Performance of steam ejector with nonequilibrium condensation for multi-effect distillation with thermal vapour compression (MED-TVC) seawater desalination system

The single-phase and two-phase flow models are developed and compared for the performance evaluation of a steam ejector for the multi-effect distillation with thermal vapour compression (MED-TVC) seawater desalination system. The results show that a single-phase flow model with ignoring the phase change predicts an unphysical temperature of the steam in the supersonic flow with the minimum value of approximately 122 K, which raises the query of the formation of the ice. The two-phase wet steam model corrects the distribution of the flow parameter by predicting the heat and mass transfer during the phase change. The steam achieves the first nonequilibrium condensation process inside the primary nozzle and another four alternating condensation and re-evaporation processes. The single-phase flow model under-predicts the entropy loss coefficient by approximately 15% than the two-phase wet steam model. The performance comparison is achieved against the single-phase model to present the accuracy of the two-phase model for the steam ejector simulation. This demonstrates that the nonequilibrium condensation is essential for the performance analysis of steam ejectors for MED-TVC seawater desalination system.

Numerical Simulation of Influence of Nozzle Spindle Position on the Performance of Steam Ejector

Numerical Simulation of Influence of Nozzle Spindle Position on the Performance of Steam Ejector

Numerical investigation on the influence of mixing chamber length on steam ejector performance

A steam ejector can effectively utilize waste heat resources, which is widely used in the fields of air conditioning, refrigeration, and seawater desalination. The structure of the steam ejector’s mixing chamber has a critical influence on its performance. In this paper, the effects of the mixing chamber length on the steam ejector performance under different Mach numbers at the nozzle exit, constant area section length, and diffuser length are studied using three-dimensional (3D) numerical simulations. The numerical simulation results show that the entrainment ratio and critical back pressure of the steam ejector rise first and then decrease with the increasing of the mixing chamber length under different Mach numbers, constant area section lengths and diffuser lengths. The steam ejector can achieve a better performance with the mixing chamber length in the range of 40–80 mm, when the nozzle throat diameter is 2.5 mm under a typical working condition of steam ejector refrigeration.

Optimization of the primary nozzle based on a modified condensation model in a steam ejector

The beauty and complexity of steam ejectors have fascinated scientists for decade. A modified condensation model is presented to evaluate the steam ejector performance and to optimize the steam ejector geometry. Four models consisting of different nucleation models and droplet growth models are employed to predict the non-equilibrium condensation phenomenon in a nozzle and in a steam ejector. The results show that the modified condensation model is more appropriate than the other three models. The internal flow structures as well as p-h diagram are applied in the steam ejector performance analysis. The results show that the steam ejector entrainment ratio predicted by the modified condensation model is smaller than the value predicted by the dry gas model. Given that the nucleation process mainly occurs in the steam ejector primary nozzle, only the primary nozzle is optimized using the Multi-Objective Genetic Algorithm method based on the modified condensation model. The optimal results indicate that the entrainment ratio of the optimized steam ejector increases by about 27.5% against the original value. The findings are of fundamental and practical relevance. It hopes that experimenters will be motivated to check our predictions.

Improvement of the wet steam ejector performance in a refrigeration cycle via changing the ejector geometry by a novel EEC (Entropy generation, Entrainment ratio, and Coefficient of performance) method

In this research, the improvement of an ejector performance has been studied as crucial part of an ejector refrigeration system by means of applying changes in its geometry. Water steam is taken as a non-expensive, non-toxic, and available refrigerant and wet steam model has been employed to more accurate numerical simulation and analysis. It is investigated the effect of changing geometric parameters according to the presence of wetness in the flow field. The geometric parameters are the length and diameter of the constant area section of the ejector and the diameter of primary nozzle throat. In addition to entrainment ratio (ER) and critical compression ratio (CR) of the ejector as conventional design criteria, COP of the refrigeration system and the total entropy generation (EG) in the flow inside the ejector are also used; which results in a novel EEC (Entropy generation, Entrainment ratio, and Coefficient of performance) method for ejector design in the ejector refrigeration systems. The impact of changing each geometry parameter is examined in a separate process. Finally, the increment in the length and diameter of the constant area section and decrement in the diameter of the primary nozzle throat are considered as desirable changes. Consequently, by applying these changes ER and COP have improved by 32% and total entropy generation is decreased.

Performance evaluation and operation optimization of the steam ejector based on modified model

Steam ejectors are widely applied in various industries, as they have the ability to improve the low-grade energy. In this work, a modified model is proposed and employed to evaluate steam ejector performance and to optimize steam ejector operation. Firstly, the modified nucleation model is built. Four models consisting of different nucleation models and droplet growth models are adopted to predict the non-equilibrium condensation. The results show that the model consisting of the modified nucleation model and Young′s droplet growth model (ϕ=0.75,α=9) presents the best ability to predict pressure distribution and the Wilson point than the other three models. Secondly, a steam ejector is investigated using the modified model and the ideal gas model, the results show that the modified model is more suitable to predict the steam ejector wall pressure distribution than the ideal gas model, and the steam ejector performance predicted by the modified shows less error than that predicted by the ideal gas, compared with that obtained by the experiment. The relative error of critical condenser pressure reduces from 4.4% to 1.5%. At last, the steam ejector operation is optimized based on the modified model, and the results is analyzed in sufficient detail.

Experimental Investigation of the Steam Ejector in a Single-Effect Thermal Vapor Compression Desalination System Driven by a Low-Temperature Heat Source

The paper presents an experimental investigation of a steam ejector in a single-effect thermal vapor compression (S-TVC) desalination system driven by a low-temperature (below 100 °C) heat source. To investigate the performance of the steam ejector in the S-TVC desalination system, an experimental steam ejector system was designed and built. The influences of the nozzle exit position (NXP), operating temperatures, and the area ratio of the ejector (AR) on the steam ejector performance were investigated at primary steam temperatures ranging from 40 °C to 70 °C, and at secondary steam temperatures ranging from 10 °C to 25 °C. The experimental results showed that the steam ejector can work well in the S-TVC desalination system driven by a low-temperature heat source below 100 °C. The steam ejector could achieve a higher coefficient of performance (COP) by decreasing the primary steam temperature, increasing the secondary steam temperature, and increasing the AR. The steam ejector could also be operated at a higher critical condensation temperature by increasing the primary steam temperature and secondary steam temperature, and decreasing the AR. This study will allow S-TVC desalination to compete with adsorption desalination (AD).

Numerical study for the influences of primary steam nozzle distance and mixing chamber throat diameter on steam ejector performance

The geometry and operation parameters have important influences on the performance of steam ejectors. An axisymmetric two-dimensional mathematical model for transonic compressible flow inside a steam ejector has been established in this paper to investigate the flow characteristics inside steam ejectors aiming at optimizing primary steam nozzle exit section distance and mixing chamber throat diameter simultaneously. The results show that there are an optimum value for the primary steam nozzle distance ratio and an optimum diameter ratio of mixing chamber throat to primary nozzle throat at which the steam ejector acquires its best entrainment performance under the given design conditions. With the optimized primary steam nozzle distance, the optimization of the diameter ratio of the mixing chamber throat to primary nozzle throat is significant. In our case, the improvement of the entrainment ratio is as large as 25%. Deviation from its optimized value may result in a serious degeneration in the ejector performance. Therefore, to ensure the steam ejector performance, the primary steam nozzle distance should be designed at its optimum value and the diameter ratio of the mixing chamber throat to primary nozzle throat be within a narrow vicinity of its optimum value.

Combined auxiliary entrainment and structure optimization for performance improvement of steam ejector with consideration of back pressure variation

It is crucial to enhance the entrainment performance of steam ejectors which operate under double-critical conditions to widen their application in industries. In this paper, combined auxiliary entrainment technical approach is proposed and corresponding geometric structure optimization has implemented systematically, for a better use of the inside low-pressure potential thus greatly improving the entrainment performance of the steam ejector under double-critical conditions. Moreover, a comprehensive analysis and discussion of the influence of the geometrical parameters on the auxiliary entrainment performance has been obtained from mass flow rate, pressure field and special internal flow characteristics. The results reveal that the combined auxiliary entrainment is the best choice for the given steam ejector operating under the double-critical conditions, and the optimum geometrical parameters of throat auxiliary entraining entrance are same as the designed condition and remain unchanged. For the diffuser auxiliary entraining entrance, the opening starting position Xs could be set at the entrance of the diffuser identically, the opening angle could be chosen as a common range Rθ from 75° to 105°. However, the optimum opening width d increases with the decrease of back pressure pC. In general, there is an optimum geometrical parameters combination that the entrainment performance can achieve its maximum value for each pC. The smaller the pC, the bigger the entrainment ratio improvement, as large as 34.8% for pC of 32 kPa.

Pitot and static pressure measurement and CFD simulation of a co-flowing steam jet

Condensation in the primary nozzle of a steam ejector changes the steam jet properties during the nozzle expansion process and affects the mixing rate of the primary and secondary streams and thus the performance of steam ejectors. Only limited experimental data is available for the mixing of wet steam jets at conditions relevant to steam ejectors. The present work provides static and pitot pressure measurements within a wet supersonic steam jet which mixes with a low pressure co-flowing secondary stream. High pressure steam was delivered to the primary nozzle at a stagnation pressure and temperature of 270 kPa and 406 K, respectively. The primary nozzle throat diameter was 3.2 mm and its exit diameter was 13.6 mm. Pitot and static pressure measurements were obtained on the mixing jet centreline from the nozzle exit to a downstream location of 185 mm in the mixing chamber. Radial profiles of pitot and static pressure were also measured at positions of 5, 20, 35, 85, 135 and 185 mm downstream of the nozzle exit. With the mixing chamber pressure maintained at approximately 1.3 kPa, the mixing jet was in an under-expanded condition. CFD simulations with a non-equilibrium wet steam model also demonstrate the under-expanded jet structure. The pitot pressure profiles at the furthest locations downstream (135 and 185 mm) show reasonable agreement between experiments and simulations in terms of the spreading of the jet due to turbulent mixing. However, there are significant differences between the experimental and simulated pitot and static pressures profiles in the transverse and axial directions. Contributions to these differences are likely to arise because the simulated static pressures in the under-expanded wet steam jet core are lower than the triple point for water (0.61 kPa), so potential exists for liquid-solid and vapour-solid phase transitions that are not currently modelled in the simulations.

Effect of a mixture of carbon dioxide and steam on ejector performance: An experimental parametric investigation

The results are presented for an experimental investigation characterizing the performance of a steam ejector when the secondary fluid is a mixture of steam and a non-condensable gas. In the context of post-combustion carbon capture, carbon dioxide was chosen as the non-condensable for this work. In order to study the pure steam ejector over a wide operating range, performance curves were prepared for primary pressures of 350, 450 and 550 kPa, with secondary pressures of 50, 70 and 90 kPa. Effects of the primary nozzle position, the primary pressure, the secondary pressure, and the nozzle diameter were evaluated. For a reference primary pressure of 450 kPa and secondary pressure of 70 kPa, performance curves were prepared for four levels of entrained CO2 in the secondary fluid mixture, up to 45% by mass, and for four nozzle throat diameters ranging from 4.03 to 5.09 mm. It was observed for the first time that in contrast with the pure steam ejector performance curves, increasing amounts of entrained CO2 improved the critical entrainment ratio, but the critical pressure remained unchanged. This behaviour was in sharp contrast with that of a pure steam ejector. A linear relationship was observed between the increase in the entrainment ratio of a steam ejector and the mass fraction of CO2 contained in the ejector secondary fluid.

A Numerical Study for Predicting Steam Ejector Performance at Different Pressure Ratios

This paper presents a numerical study for predicting the steam ejector performance for different pressure ratios. The considered steam ejector operates at small pressure ratios of back to motive pressures. Both the suction and motive fluids are regarded to be dry steam. Due to low pressure created by the motive steam nozzle flow, entrainment of steam to be mixed with motive steam where both resume flowing toward the ejector exit. Mass ratio of suction to motive flows is an important element to describe the ejector performance.The present study aims to optimize the steam ejector efficiency that runs at different pressure ratio for each suction pressure. The variation of the mass ratio and ejector efficiency with the ejector back pressure at different values of the suction pressure and constant motive pressure, also a variation of the mass ratio and ejector efficiency with the ejector back pressure at different values of the motive pressure and constant suction pressure are investigated. The numerical results are validated with the available experiments from the literature. The results show that the mass ratio is almost constant at low values of back pressure, depending on the suction and back pressures, then the mass ratio decreases sharply with increasing the back pressure. The suction pressure has the positive consequence on the mass ratio. Moreover, the results show that the ejector efficiency increases with increasing the back pressure to gain its upper limit value, subsequently that the efficiency decreases with raising the back pressure. Also, raising the suction pressure will cause an improvement in the ejector efficiency. The value of back pressure at which the maximum efficiency is achieved and its value increases with magnifying the suction pressure.

A Numerical Study for Predicting Steam Ejector Performance at Different Pressure Ratios

A Numerical Study for Predicting Steam Ejector Performance at Different Pressure Ratios

Numerical study for the influences of primary nozzle on steam ejector performance

The influences of primary nozzle on the performance of steam ejectors were investigated numerically, and the effects of the primary nozzle outlet diameter as well as the divergent section length under different entrained stream pressures on the steam ejector were analyzed and discussed. The results revealed that the entrainment ratio of steam ejector initially increases sharply with the primary nozzle outlet diameter and then decreases after the outlet diameter exceeds a certain value. Therefore, there is an optimum range for the primary nozzle outlet diameter at which the ejector obtains its best performance. It was also disclosed that the divergent section length has only a comparatively weak effect on the ejector performance. The entrainment ratio increases slowly first with the divergent section length to its maximum and then decreases gradually due to the increase of flow frictional drag. Hence there also exists an optimum value for the divergent section length at which the steam ejector performs best. However, it should be stressed that this largest entrainment ratio corresponding this optimum divergent section length differs little from the non-optimum value which means we can design the divergent section with a wider range of the length.

Effect of mixing on the performance of wet steam ejectors

Steam ejector computational simulations using a wet steam model give higher entrainment ratios and higher critical back pressures for the ejector compared with the ideal gas model. This paper identifies the origin of these differences. Simulation results show that the wet steam model predicts an entrainment ratio for the choked flow ejector operation that is 10% higher than that for the ideal gas model. The wet steam model also gives a higher critical back pressure by about 7% relative to the ideal gas model with a closer agreement to experimental data for the unchoked ejector operation. Enhanced mixing layer growth which arises due to steam condensation in the primary nozzle is identified as the main reason for higher entrainment ratio of the ejector simulations using the wet steam model. The difference in the mixing layer growth rate between ideal gas and wet steam simulations is 21%, indicating enhanced entrainment for the wet steam model. Furthermore, the mixture at the start of the diffuser is shown to have a higher pitot pressure than in the ideal gas simulations and these elevated pitot pressures allow the ejector to operate in a choked mode to a higher critical back pressure.

Numerical Study on condensation Process of Steam Flow in Nozzles

Steam ejector is an important component in engineering applications, which require high vacuum, such as steam plant condenser. Prediction of steam ejector performance is very significant tool for the design of the ejector. The steam ejector consists of three parts; nozzle, mixing chamber and diffuser. The nozzle has the task of creating the vacuum required. In the current paper numerical treatment of wet steam flow through the nozzle of an ejector is presented. The first task of this work is to test and evaluate several turbulence models on a generic case, constructed for turbulent steam flow in a convergent-divergent nozzle. The effect of pressure ratios, that is responsible for controlling the location or absence of the generated shock wave as well as the impact of the shock wave on the condensation of steam inside the nozzle are numerically concerned. These features are clearly observed from the pressure distribution, Mach number, liquid mass fraction, droplet nucleation rate, droplet critical radius and static temperature. It is concluded from the current work that the standard k-ω model is the most appropriate turbulence model for simulating this complex flow compared to the other considered models for nozzle steam flow sumulation.