Steam Ejector Research Articles

Three-dimensional numerical simulation and structural optimization of large steam ejectors in exhaust gas heat recovery systems

By establishing a three-dimensional mathematical model based on the physical characteristics of the steam ejector and utilizing computational fluid dynamics (CFD) method, this study conducted three-dimensional numerical simulations to investigate the effects of five key structural parameters, namely, the length of the nozzle diffuser section, the diameter of the nozzle outlet, the length of the contraction section in the mixing chamber, the diameter of the mixing chamber inlet, and the length of the mixing chamber throat, on the ejector performance under identical operating conditions. By fitting 50 sets of simulation data using the least squares method, analytical expressions for these structural parameters in terms of the ejection coefficient μ were obtained. Subsequently, an improved firefly algorithm was employed to identify the optimal combination of structural parameters, followed by simulation verification. The results showed that compared to the single-factor sensitivity analysis method, the improved firefly algorithm obtained a superior combination of structural parameters, resulting in a 2.03% enhancement in the ejection performance of the steam ejector.

A study of the application of wet steam modeling for thermocompressor simulation in TVC desalination

Recently, the wet steam model, grounded in classical nucleation theory, has been utilized for computational fluid dynamics (CFD) simulations of thermocompressors and steam ejectors. However, this model, which accounts for the formation of liquid droplets in a homogeneous non-equilibrium condensation process, presents computational challenges due to its complexity. Unlike the ideal gas model, it involves solving multiple equations concurrently with the Navier-Stokes equations, rendering it computationally intensive and difficult to converge. The primary objective of this study is to evaluate the feasibility and efficacy of employing this intricate wet-steam model for modeling steam thermocompressors, specifically analyzing its impact on pressure, temperature, and Mach number contours. This paper aims to investigate the influence of modeling non-equilibrium condensation on various parameters affecting ejector performance. Utilizing numerical simulations conducted via ANSYS Fluent software, employing both 2-D axisymmetric wet steam and ideal gas models, our study reveals that non-equilibrium condensation leads to a higher entrainment ratio and critical back pressure. Additionally, our findings indicate that while the wet steam model notably affects temperature contours, its effect on pressure and velocity contours is comparatively minimal. The CFD analysis found that pathline trajectories were similar with both ideal gas and wet steam models. Droplet formation and evaporation within the thermocompressor revealed a gradual evaporation up to the midpoint of the constant area section, followed by a rise in liquid mass fraction due to droplet formation. However, after the constant area section, a shock wave led to a sudden pressure increase and decrease in liquid mass fraction of wet steam. These changes persist through the diffuser section of the ejector.Furthermore, to enhance the reliability of our results, this research integrates a robust validation methodology. We compare experimental results obtained from ejector studies in the literature with our simulations. Moreover, we introduce an experimental section in our research, specifically addressing zero suction mass flow rate conditions, thereby offering a practical validation approach.

Numerical simulation of blade-type adjustable steam ejector

As a kind of pressurizing equipment, the ejector has some problems, such as low efficiency and poor anti-wave ability. The design of the adjustable ejector can improve the efficiency of ejector and broaden the application range. In this paper, a blade-type adjustable ejector is proposed for the first time. Firstly, the computational fluid dynamics model is established and verified by experimental data. The effects of different working pressures, blade openings and back pressures on the blade-type adjustable ejector performance are analyzed, and we also analyze the influence of blade geometric parameters (blade angle, blade height, blade number) on the blade-type adjustable ejector. Compared with the traditional fixed steam ejector, when the working conditions change, by changing the geometric parameters of the blade-type adjustable ejector, the entrainment ratio of the blade-type adjustable ejector is always greater than 0.71 and the efficiency is always greater than 13%. The entrainment ratio can be increased by 204% and the efficiency can be increased by 8.49%. In addition, the geometrical parameters of the blade are optimized and the sensitivity analysis is carried out by orthogonal test, which further improves the performance of the ejector. According to the sensitivity analysis results, the order is: blade number, blade height, blade angle. When the working condition changes, the ejector designed in this paper can operate efficiently in a wide working range by adjusting its parameters. At the same time, this study broadens the research direction of the adjustable ejector and provides more extensive reference for the design of the adjustable ejector.

Simulation and Experimental Investigation of Performance and Flow Behavior for Steam Ejector Refrigeration System

The ejector refrigeration system is a desirable choice to reduce energy consumption. A Computational Fluid Dynamics CFD simulation using the ANSYS package was performed to investigate the flow inside the ejector and determine the performance of a small-scale steam ejector. The experimental results showed that at the nozzle throat diameter of 2.6 mm and the evaporator temperature of 10oC, increasing boiler temperature from 110oC to 140oC decreases the entrainment ratio by 66.25%. At the boiler temperature of 120oC, increasing the evaporator temperature from 7.5 to 15 oC increases the entrainment ratio by 65.57%. While at the boiler temperature of 120oC and the evaporator temperature of 10oC, increasing the nozzle throat diameter from 2.4 to 2.8 mm decreases the entrainment ratio by 40%. The numerical results showed that reducing the condenser back pressure or increasing the primary fluid temperature, secondary fluid temperature, and nozzle throat diameter moves the second shock waves in the downstream direction. It could be concluded that the second shock series position detects the ejector operation mode. The ejector runs in critical mode if the second shock series position is close to the diffuser. In contrast, if the second shock series position moves toward the upstream, the ejector runs in subcritical mode.

Performance Evaluation of a Steam Ejector Considering Non-Equilibrium Condensation in Supersonic Flows

Performance Evaluation of a Steam Ejector Considering Non-Equilibrium Condensation in Supersonic Flows

Numerical Investigation on the Effect of Wet Steam and Ideal Gas Models for Steam Ejector Driven by Ship Waste Heat

Steam ejectors could improve the energy efficiency of ships by efficiently utilizing low-grade waste heat from ships for seawater desalination or cooling. The internal flow characteristics of steam ejectors can be deeply analyzed through numerical simulation, which is of great significance for improving their performance. Due to the influence of the nonequilibrium phase change, the results of the wet steam model and the ideal gas model are significantly different. In this paper, the flow field characteristics of the wet steam model and the ideal gas model under different primary flow pressures (Pm) are compared and analyzed. The results show that the structures of the shock wave train for the wet steam model and the ideal gas model are different under different Pm. When the first shock wave of the shock wave train changes from a compression shock wave to an expansion shock wave, the Pm for the ideal gas model is 75,000 Pa and that for the wet steam model is 55,000 Pa. The phase change reduces the energy loss of the shock wave. With the increase in the Pm, the variation in the length of the shock wave train for the wet steam model decreases by 61%, the variation of the primary temperature at the nozzle exit increases by 60% and the variation in the choke temperature decreases by 50% compared with the ideal gas model. The investigation in this paper provides guidance for the design theory of a ship waste heat steam ejector.

An Ejector and Flashbox-Integrated Approach to Flue Gas Waste Heat Recovery: A Novel Systematic Study

In this study, a comprehensive examination was conducted to explore the technology involved in the recovery of waste heat from flue gas emitted by a 1000 MW unit. Traditional methods are constrained in their ability to harness waste heat from flue gas solely for the purpose of generating medium-temperature water. The system being examined not only recovers waste heat but also utilizes it to generate steam, thereby greatly improving resource efficiency. The process entails utilizing the flue gas to heat water to a certain temperature, followed by subjecting it to flash evaporation. This process leads to the generation of low-pressure waste heat steam. Within the steam ejector, the waste heat steam combines with high-pressure motive steam extracted from the source, resulting in the formation of medium-pressure steam. Within the steam ejector, the waste heat steam blends with high-pressure motive steam drawn from the source, forming medium-pressure steam that eventually feeds into the A8 steam extraction pipe (low-pressure turbine pumping pipe). The present study examines the fluctuation patterns in motive steam flow, suction coefficient, waste heat steam volume, and outlet temperature of the flue water heat exchanger when different motive steam sources are used. Additionally, the research calculates the reduction in CO2 emissions, the coal consumption for power supply, and the cost savings in fuel for the retrofitted system. The findings indicate that maximizing energy utilization can be achieved by operating the retrofitted unit at the lowest feasible waste heat steam pressure. The implementation of the new system has resulted in a substantial decrease in coal consumption for power supply. When employing main steam as the extraction steam source, the consumption of coal for power generation decreases in proportion to the decrease in waste heat steam pressure while maintaining a constant unit load. When the waste heat steam pressure reaches 0.0312 MPa, the recorded coal consumption for power generation varies between 289.43 g/kWh at 100% turbine heat acceptance (THA) and 326.94 g/kWh at 30%THA. When comparing this performance with the initial thermal power plant (TPP) unit, it demonstrates reductions of 2.26 g/kWh and 1.52 g/kWh, respectively. After implementing modifications to this 1000 MW unit, it is projected that the annual CO2 emissions can be effectively reduced by 6333.97 tons, resulting in significant cost savings of approximately USD 0.23 million in fuel expenses. This system exhibits considerable potential in terms of emission reduction and provides valuable insights for thermal power plants aiming to decrease unit energy consumption.

Energy and exergy analysis of primary steam superheating effects on the steam ejector applied in the solar renewable refrigeration cycle in the presence of spontaneous nucleation

Abstract The generator energy consumption in the renewable refrigeration cycles is supplied by solar energy, geothermal energy and waste heat. The thermal energy of low grade can be utilized to superheat the vapour in a generator of the refrigeration cycle. The effect of primary flow superheating was examined on the renewable refrigeration cycle performance using the wet steam model in the ejector. The vapour’s degree of superheating was selected in the 0–100 K range. The superheating level effects were investigated on parameters (wet steam, entrainment ratio, energy consumption, COP, second law efficiency and exergy destruction). The aim of this study is a comprehensive evaluation of the effect of superheat on the ejector refrigeration cycle and the flow behavior in the steam ejector simultaneously. The results represented that superheating the inlet steam in the primary nozzle weakens the spontaneous condensation intensity and delays the condensation shock, the combining process between the secondary flow and the primary flow is improved, and the entrainment ratio is increased, the generator energy consumption and the efficiency of the second law are decreased, the exergy destruction in the ejector is reduced, and the total exergy destruction of the refrigeration cycle is increased. Considering the second law efficiency, COP, the entrainment ratio and the energy consumption, a temperature of 40° of the superheat was achieved as the best degree of the superheat in this cycle that in comparison to the state without superheating, the entrainment ratio and COP are increased by 4.4 % and 1 %, the second law efficiency and the generator energy consumption are reduced by 19.5 % and 1.6 %, respectively.

Supersonic Nozzle Location in Steam Ejector Effect on the Mass Fraction and Vacuum of Second Fluid

Supersonic Nozzle Location in Steam Ejector Effect on the Mass Fraction and Vacuum of Second Fluid

Integration model and performance analysis of coupled thermal energy storage and ejector flexibility retrofit for 600 MW thermal power units

A flexible retrofitting method for thermal-energy-storage-coupled thermal power units is proposed. The exergy flow Sankey diagram and efficiency of the three charging methods was analyzed in detail, and comparative data were provided. The new thermal energy storage mode coupled with steam ejectors was the optimal solution, with a significantly higher round-trip efficiency than the published results. Further study of the mode revealed slight temperature variations in the molten salt did not affect system efficiency. As the extraction of reheated steam decreases and the extraction of main steam increases, the minimum generation capacity of the unit decreases continuously, reaching a minimum of 40 MW (6.67%). In contrast, the maximum output of the unit at 100% THA release can reach 682 MW, which caused the unit load to change from 26-100% to 6.67–113.67% before and after the retrofit. As the ejection coefficient increased, the round-trip efficiency increased significantly, corresponding to 73%, 77%, and 80% at the study points. The mathematical model based on principal component analysis can effectively characterize the relationship between the ejection coefficients, extraction of main steam, extraction of reheat steam, low valley peaking rate, peak modulation rate, and round-trip efficiency, providing a signal conversion basis for automatically controlling peaking commands during unit operation. Finally, the benefits before and after retrofitting were analyzed in terms of thermal plant operation, proving that the payback period of the system was 4.09 years. Peak tariff and auxiliary service revenue are the most critical parameters affecting the payback period, and a 10% reduction in the peak tariff corresponds to an increase in the payback period of one ∼ two years. The results of this study provide substantial theoretical and practical guidance for the flexible retrofitting of thermal power units.

Numerical investigation of the effects of dry gas model and wet steam model in solar-driven refrigeration ejector system

Abstract Nowadays, the use of equipment with little pollution is essential due to the increase in the planet’s temperature. Ejectors are considered one of the equipment with no pollution, and their failure rate is low due to the lack of moving parts. Also, scholars have recently focused on improving the efficiency of industrial equipment. The use of accurate modeling is required to improve steam ejector performance. In a steam ejector, non-equilibrium condensation creates a two-phase flow situation. The wet steam model, used in this study, characterizes this two-phase flow. The study’s objective was to compare this wet steam model with the dry gas model. In the wet steam model, the liquid mass fraction is 0.25, and its calculated entrainment ratio is lower than the dry gas model, closely matching experimental observations. The dry gas model reaches a maximum Mach number of about 5, while the wet steam model approximates 4. A significant temperature difference exists between the two models, with the dry gas model indicating lower temperatures compared to the wet steam model. Diagonal shocks and expansion waves are evident in the mixing chamber, fixed cross-section, and diffuser. These phenomena occur with greater intensity and a slight delay in the wet steam model compared to the dry gas model.

Design and optimization of a multi-level wasted heat recovery system for a natural gas-based gas turbine cycle; comprehensive exergy and economic analyses

The increasing demand for power and the imperative of harnessing wasted heat to optimize power systems have motivated this current study. The main goal is conceptualizing an innovative multi-generation plant fueled by natural gas, which ingeniously integrates four distinct cycles: steam Rankine, absorption power, ejector refrigeration, and proton exchange membrane electrolyzer. This integration is synergistically coupled with a gas turbine to elevate overall system performance significantly. The investigation extends to the thorough examination, including the system's energy, exergy, and economic attributes, facilitating an all-encompassing assessment of the newly conceived plant's efficiency. Through a meticulous parametric inquiry, the study scrutinizes the influence of various parameters on the operational prowess of the system. Moreover, the quest for optimum performance unfolds through a multi-objective optimization process conducted across three distinct scenarios. Regarding the outcomes, at the base operating conditions, the novel system exhibits the capacity to yield 3,896.6 kW of net power, additionally generating a cooling load of 77.7 kW and producing 0.22 kg/h of hydrogen. Notably, it attains an exergy efficiency of 47.1 %, with the combined unit cost of products and a commendable payback period measuring at 9.16 $/GJ and 1.4 years, respectively, under baseline conditions. The preeminent role in exergy destruction is attributed to the gas turbine cycle, accounting for 88.59 % of the total, while the highest share of the total investment cost is allocated to the turbines. The pinnacle of optimal performance is realized in a state wherein the system achieves its zenith in terms of efficiency and output, reflecting the culmination of meticulous design and analysis.

Performance and economic analysis of steam extraction for energy storage to molten salt with coupled ejector and thermal power units

A new thermal power unit peaking system coupled with thermal energy storage and steam ejector was proposed, which is proved to be technically and economically feasible based on the simulation of a 600 MW thermal power unit. Results show that the percentage of exergy losses in the retrofitted system is in the order of condenser, turbine and thermal energy storage system, with the exergy losses in the heat release process accounting for approximately 70 % of the cycle. The condenser and evaporator corresponding to the storage and heat processes account for 60 % of the total exergy losses in thermal energy storage system. The retrofitted system has a maximum cycle efficiency of 70–80 % with low and peak modulation rates of 16.5 % and 11.7 %. Extraction of main steam dominates the peaking rate and cycling efficiency compared to extraction of reheat steam. Increasing the main steam pressure at the ejector inlet increases the low peaking rates by 1.5 %, while reducing the molten salt flow rate per unit peaking depth by 10 t/h, which is essential for the stable operation of the retrofitted system. The economic analysis of the retrofitted system shows that the system operating time is the main factor affecting the payback period compared to the interest rate and starts to be profitable in 3.8 years, with later profitability of up to RMB 25 million/year. Further analysis reveals that two different extractions of reheat steam with the same extraction of main steam will achieve the same payback period, which offers a variety of possibilities for practical operational scenarios. In addition, when the extraction of main steam is <250 t/h, the payback time of the system will exceed 15 years, at which point it will be challenging to meet the economic viability of the retrofitted system.

Comparative analysis on thermodynamic performance of combined heat and power system employing steam ejector as cascaded heat sink

Comparative analysis on thermodynamic performance of combined heat and power system employing steam ejector as cascaded heat sink

Numerical Analysis of Steam Ejector Performance with Non-Equilibrium Condensation for Refrigeration Applications

In recent years, there has been great interest in developing cooling systems with humidity- and temperature-independent control capabilities that can operate efficiently at varying temperatures. This paper proposes a bi-loop double-evaporator ejection–compression cycle, which utilizes low-grade heat and is suitable for the construction industry. The proposed cycle involves the concurrent operation of a vapor compression cycle and an ejector refrigeration cycle that enables it to handle altered pressure levels and operate with varying compression ratios all the way to a common condenser pressure. Conventional computational fluid dynamics (CFD) approaches often model steam as an ideal gas with single-phase flow. In contrast, this research employs the wet steam model to optimize ejector geometry. The wet steam model takes into account non-equilibrium water vapor condensation, thus providing a more precise assessment of spontaneous condensation behavior and its impact on ejector performance. When compared to the conventional dry gas model, the use of the wet steam model dramatically decreases the entrainment ratio error from 16.24% for single-phase steam to 3.92% when compared to experimental data. This study concentrates on four critical attributes of wet steam, including Mach number, droplet nucleation rate, average droplet radius, and liquid mass fraction, to develop a strategy for enhancing ejector performance and efficiency. The study demonstrates that optimal area and primary nozzle diameter ratios for the steam ejector are 5 and 2.4, respectively. Increasing the area ratio mitigates condensation intensity, thereby reducing the liquid mass fraction in the diffuser. Overall, this paper provides valuable insights into improving and optimizing ejector performance, thus highlighting the importance of considering the behavior of spontaneous condensation in ejector design and modeling.

Performance and mixing process investigation of a novel mixing-enhanced ejector

Ejector refrigeration systems rarely require electrical energy, satisfying the requirements of sustainable development and low carbon emissions. However, owing to the limitations of the operating conditions, the ejector performance is not sufficient, and there is an urgent need to improve the entrainment performance of the ejector. In this study, experiments and numerical simulations were performed on a conventional ejector, and the numerical simulation results were fitted with the experimental data. A numerical simulation was used to investigate the mixing process and entrainment performance of the novel mixing-enhanced supersonic steam ejector. The optimal values of lm = 120 mm and dc = 57.5 mm achieved the best entrainment ratio (0.778) for the novel ejector under 5%-tab blockage ratio. The results showed that the entrainment performance of the novel ejector improved by 51.1–54.7% and 10.5–12.3% compared to those of the conventional ejector and the conventional ejector with an adjusted mixing chamber, respectively. This was because the generated streamwise vortices entrained more secondary flow into the mixing chamber, and the mixing process between the primary and secondary flow avoided unnecessary kinetic energy loss, increasing the mixing efficiency and accelerating the secondary flow crashing out of the diffuser.

Investigation on improvement potential of steam ejector performance in refrigeration cycle via constant rate of momentum change design method

In this paper, an ejector created by the constant rate of the momentum change method (CRMC ejector) was experimentally studied and compared with the widely used constant pressure method (CPM ejector) under the same ejector area ratio. The influence of the boiler temperature, evaporator temperature, and primary nozzle size on the ability to improve the performance of the CRMC ejector was examined. The results indicated that at the same ejector area ratio, the CRMC ejector always performed a higher mass entrainment ratio than the CPM ejector. However, the critical condenser pressure was similar. The average percent improvement of the entrainment ratio via the CRMC ejector was approximately 20%. Based on the photograph taken from the transparent ejector, a compression shock wave was still found in the flow process of the CRMC ejector. This shows that an improvement potential of the CRMC ejector does not concern the compression shock wave as proposed in the design theory. The key to improvement was believed to be its ability to mitigate the momentum loss during the mixing process. In such a case, some simulation works based on computational fluid dynamics (CFD) were employed for explanation. This can also confirm that the compression shock wave via CRMC ejector is still found. In addition, this paper compared the experimental results with the theoretical results obtained from 1-D theory and CRMC theory to alternatively discuss that an improvement potential of the CRMC ejector was mainly the cause of a lower mixing loss.

Numerical Study on Flow and Noise Characteristics of High-Temperature and High-Pressure Steam Ejector

Based on the shear stress transfer (SST) k-ω model, Ffowcs-Williams and Hawkings (FW–H) equation, and Lilley sound source equation, the flow and sound field of high-temperature and high-pressure steam ejectors are simulated. The entrainment performance, near-field sound source, and far-field noise of the steam ejector are discussed. The influences of working parameters including the primary steam pressure, the secondary steam pressure, and the back pressure are analyzed. The results show that under the design conditions, the steam ejector has two shock waves and three sound source regions. A shear layer at the boundary of the first shock wave generates the Sound source-I, and the flow separation at the boundary of the second shock wave causes the Sound source-III. The Sound source-II is located near the mixing chamber wall and the sound pressure levels around the ejector depend on the distances from the Sound source-II. In terms of the entrainment performance, with the increasing primary pressure or the decreasing secondary pressure, as the driving pressure difference of the secondary steam decreases, so does the entrainment ratio. As the back pressure increases, the entrainment ratio firstly remains constant, and then rapidly decreases when the back pressure exceeds the critical value at pb = 5.5 MPa. In terms of the noise characteristics, the sound pressure level and the intensity of the second shock wave have a positive correlation. When the primary or secondary pressure increases, the sound pressure level increases. Moreover, with the increasing back pressure, the sound pressure level firstly decreases, reaches the minimum of 98.2 dB at the critical back pressure, and then slowly increases.

Investigation and development of improved methods for the design of ejector

The ejector is a simple mechanical device having no moving parts has the characteristics of being fixed, reliable, inexpensive, simple to keep up and handle. An ejector is a device that allows a fluid at low pressure flow (secondary fluid flow) by speed up some other fluid at high pressure flow (primary fluid flow) through nozzle. It is used in lot of industrial processes, particularly with air or steam as operating fluid. The ejector system has a vast range of applications. They reduce pollution compared to fossil fuel power plants. The geometry of the ejector has a remarkable impact on the performance of the ejector. A steam ejector can effectively make use of unused heat resources, which is mainly used in air conditioning, refrigeration, and seawater desalination sectors. The geometry of mixing chamber of the steam ejector features a critical effect on its outcome. The numerical simulation results shows that the entrainment ratio and critical back pressure of the steam ejector initially increases and then decreases with the increase in mixing chamber length for different mach numbers. Mixing chamber length of 40 mm to 80 mm and nozzle throat diameter 2.5 mm provides high performance of steam ejector for steam ejector refrigeration.Ejector with converging-area chamber has higher performance than ejector with constant area section. Hydrocarbon ejector cooling applications is highly recommended.

Comparative designs and optimizations of the steam ejector for a CHP system

High-efficiency heating in the combined heat and power (CHP) system is considered a promising strategy for energy conservation and emission reduction with the explosion of the heating demands. To recover the excessive waste heat from the exhaust steam and reduce the exergy destruction of the heating supply, we proposed a novel CHP cascade heating system integrated with a steam ejector and carried out research about ejector comparative designs and optimizations. Three methods were applied for the ejector designs in a CHP system and the software Fluent was used for numerical simulation to analyze and compare the performance and internal flow characteristics of the ejector. The ejector designed with the optimized thermodynamic method yielded the largest heating capacity and the highest system heating exergy efficiency of 212 MW and 71.0%, thus offering greater strengths for designing ejectors in the CHP cascade heating systems. On this basis, the thermodynamic performance of the designed ejector was further optimized by adjusting the structure of the mixing chamber based on the exergy analysis. The ejector entrainment ratio maximally increased by 11.4% and 6.4% through optimizing the inlet angle and the length of the contraction section of the mixing chamber. Compared with the existing ejector in the CHP heating system, the entrainment ratio of the designed ejector had a significant increment of 24.9% with a higher pressure lift ratio. Meanwhile, the heating capacity of the designed ejector and system heating exergy efficiency improved by 19 MW and 6.1%, respectively. This work provided an applicable method for the ejector designs and optimizations in a CHP system.