Entrainment Ratio Research Articles

Optimization of geometric parameters of ejector for fuel cell system based on multi-objective optimization method

ABSTRACT In this study, the multi-objective orthogonal experiment is employed to optimize the geometric parameters of the ejector. The optimization objective is determined by applying linear weighting to the entrainment ratios for 100 SLPM and 990 SLPM operating conditions. Four geometric parameters are optimized, including the nozzle exit diameter, nozzle exit position, mixing chamber length, the mixing chamber diameter. Moreover, Computational Fluid Dynamics simulations are performed, and the effects of each geometric parameter and the interaction between parameters on the performance of the ejector are ranked by range analysis. The results show that the mixing chamber diameter has the most significant impact on the optimization objective, and the degree of influence of the other factors and interactions on the entrainment ratio varies for different operating conditions. Compared with the initial parameters, the parameters obtained by the multi-objective optimization method have an average improvement of 96% in entrainment ratio over the full operating range, and the experimental results are in general agreement with the simulation results. The adaptability analysis of the ejector performance indicates that the ejector optimized by the multi-objective optimization method can meet the hydrogen excess ratio requirements for the full operating range of the fuel cell system.

Thermodynamic optimisation of a booster-ejector vapour compression refrigeration system using solar energy and R152a/Cu nano-refrigerant

Conventional vapour compression refrigeration systems require high electrical energy for low temperature applications. For the first time in the literature to reduce this required energy, comprehensive thermodynamic analysis and optimization of booster-assisted ejector expansion vapour compression refrigeration system with R152a/Cu nano-refrigerant are presented for low-temperature applications. Solar panels are used to cover the total compressor work, using the climate data of Izmir, Turkey. According to the thermodynamic optimization findings, the use of nanoparticles in the refrigeration system led to several improvements when compared to the R152a refrigeration system. These enhancements include a reduction of 6.52-11.71% in the main compressor discharge temperature, a decrease of 18.46-34.48% in the total exergy destruction rate, an increase of 3.08-4.04% in the entrainment ratio, a reduction of 0.089-3.25% in the ejector area ratio, a decrease of 8.34-14.27% in the panel area, and an increase of 8.09-14.05% in both the coefficient of performance and exergy efficiency. Another thing worth mentioning is that coefficient of performance and exergy efficiency improved by 2.06% and 1.96%, respectively, while total exergy destruction reduced by 4.83% compared to our previous study. The results obtained from the thermodynamic optimisation provide a useful reference for the design of an experimental system, as they provide evidence of model validity and can guide the implementation of the system.

Modeling, control and analysis of a novel energy-saving oriented fuel cell anode system

Fuel cell hydrogen supply sub-system needs to provide sufficient mass flow and pressure of hydrogen to meet the working demand of the stack. The hydrogen circulation pump is often used, but causes additional parasitic power of fuel cell system. In this study, a new structure of hydrogen circulation pump is proposed to reduce the parasitic power by using the pressure potential energy of hydrogen flow. The hydrogen feeding system model is established based on the solution of differential equation of state of ideal gas, mass and energy balance. Then, considering the hydrogen intake pressure and the hydrogen excess ratio of the system, a reasonable control strategy is proposed for accurate control. Simulation results show that under the fuel cell work condition and the fuel cell vehicle operation condition, pressure difference between anode and cathode and the hydrogen excess ratio can be regulated to the conditions required by the stack, and the excess ratio error and pressure difference error between anode and cathode is 3.82e-3 and 4.52e-4 Bar, respectively. The parasitic power consumption of the circulating pump is effectively reduced about two-thirds under the fuel cell vehicle operation condition. Then, the effects of anode hydrogen pressure drop, hydrogen inlet pressure and entrainment ratio of ejector on the system are studied. Reducing the anode pressure drop, increasing the ejector entrainment ratio while reducing the hydrogen inlet pressure at low power and increasing it at high power are conducive to energy-saving of the system.

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.

Performance investigation on novel combined power generation and refrigeration system

This article aims to examine a novel combined power and refrigeration system, using renewable and waste heat sources suitable for low-temperature applications. The present system is an integrated Kalina cycle and ejector refrigeration system to generate power and refrigeration simultaneously. To improve the vapour generation, the separator vapour fraction is used as a decision variable. Relative irreversibility and efficiency defect as two important parameters considered in this system for an investigation to identify the weaker components. The combined system generates power and refrigeration with two different mediums by the incorporation of the heat exchanger at the turbine exhaust. The novel system's energy and conventional exergy evaluation are carried out through Python Software. The optimum values of decision variables: turbine concentration, separator vapour fraction, entrainment ratio, expander ratio, split ratio and turbine concentration are identified using Python software from an opted range of variables. The maximum value of net power output, first law efficiency for power generation system, combined system, second law efficiency for power generation system, combined system, refrigeration effect and coefficient of performance are obtained as 113 kW, 8.85%, 11.83%, 93.44%, 81.29%, 38.07% and 0.118, respectively, at higher separator vapour fraction. Among the components considered in the combined power generation system, the condenser and LTRGN account for the higher exergy destruction rate of 30.41% and 25.53%. The coefficient of performance is maximized at a higher value of the refrigeration effect. The turbine pressure at the inlet is increased with increments in turbine work on choosing the higher value of the expander ratio. The higher exergetic value components are not emphasized to focus on improvement.

Investigation of steam ejector parameters under three optimization algorithm using ANN

Several industries have adopted Steam ejectors as promising energy-saving devices. The steam ejector is used extensively in the HVAC, refrigeration, and desalination industries because it harnesses surplus heat. Numerous computational fluid dynamics (CFD) and thermodynamic models have been addressed in the academic literature. Predictions for steam ejector parameters using these models are fairly accurate. However, considerable discrepancies between experiments and models are sometimes as high as 20 %. Contrarily, CFD simulations for an ejector are computationally expensive and necessitate careful selection and tweaking of the turbulence model. ANN-based data-driven techniques are now used for complicated mechanical system modeling. The advantages of a well-trained ANN model include low computational costs and adaptability for integration with real-time control systems. In this study, we developan artificial neural network (ANN) model of a steam ejector and analyzes how different training strategies affect the ANN model's ability to make accurate predictions. The model is trained using a sizable experimental library with various geometrical and operational conditions. Using a typology of four input factors (Nozzle Throat Diameter (Ntd), Diffuser Outlet Diameter (Dod), Ejector Area Ratio (σp), and Entrainment Ratio (ER)) that capture geometry and operating conditions characteristics, the framework predicts two output parameters: (a) Coefficient of performance (COP) and (b) Pressure reduction ratio (PRR) of the steam ejector. Among the three optimizers tested for algorithm training, the ANN model trained using the ADAM optimizer performed the best. The model's hidden layer contains 102 neurons, and a split ratio of 0.2 is used during dataset training. The average error for COP and PRR predictions made by the ANN model is ± 1.8 % and ± 2.4 %, respectively. As a result, the ANN model can be used to improve the steam ejector system's configuration and operation.

A computational study on air-entrainment and pressure distribution for natural convection cooling of a hybrid IRS device

The infrared suppression (IRS) device is an essential component of a naval warship, which passively cools the hot flue gas issuing out of the engine exhaust so as to suppress the infrared emissions. In this work, the natural convection cooling of the hot funnels of a hybrid-type IRS device has been numerically investigated in a finite volume framework by varying the diameter ratio (DR) and the Rayleigh number (Ra) in the range of 1.025 ≤ DR ≤ 1.5, and 1010≤Ra≤1012, respectively. It is observed that the Nusselt number as well the air entrainment ratio augments with the Rayleigh number. However, we noticed an initial increment in the Nusselt number with DR, and thereafter decreases marginally with a further increase in diameter ratio after attaining a peak. An optimum diameter ratio (DR = 1.1) has been obtained for the maximum heat transfer from the funnel walls. At the entry of the base and third funnel, intense suction pressure is induced, whereas the pressure recovers throughout the remaining portions of the IRS device. The influence of air entrainment on the flow and heat transfer phenomenon has been explained by delineating temperature contours, velocity vectors, and streamlines for different representative cases of the computational study. In addition, we nonlinearly regressed the computational data to propose an empirical correlation for the average Nusselt number. Furthermore, the estimation of cooling time has been done through lumped capacitance model.

Design Enhancement of Eductor for Active Vapor Transport and Condensation during Two-Phase Single-Species Flow

This study is focused on enhancing secondary vapor entrainment and direct-contact condensation in a water jet eductor for the purpose of developing a compact, medium-scale desalination system. It encompasses an extended investigation of an eductor as a condenser, or heat exchanger, for the entrained phase. Exergy study, experimental measurement, and computational analysis are the primary methodologies employed in this work. The target parameters of the optimization work were set through exergetic analysis to identify the region of maximum exergy destruction. In the case of water and water vapor as primary and secondary fluids, mixing and condensation initiates in the mixing chamber of the eductor and is where the maximum exergy destruction was calculated. Therefore, multi-jet primary nozzle eductors were studied to determine the effect of increased interphase interaction area on the exergy destruction and the maximum suction and cooling capacities. Increases in the entrainment ratio, condensation rate and heat transfer coefficient were noted for increasing numbers of nozzles when comparing one-, two- and three-jet eductors.

Single-phase air parallel ejectors: An experimental and numerical study

Ejector-based refrigeration systems (ERS) raise a lot of interest, given their lower electrical consumption compared to conventional refrigeration systems. However, a single ejector suffers from a lack of capacity flexibility, while the commercial success of this technology often relies on its ability to handle the fluctuating heating load availability and cooling load requirements. To that end, this work proposes the use of multiple ejectors having similar performance curves that could operate individually or simultaneously, according to the needs. To investigate the suitability of the proposed solution, a test bench equipped with two ejectors having different capacities, and a turbulence model, are used. The results show that the performance of the two ejectors is exactly the same, whether they are used separately or simultaneously. To the best of the author’s knowledge, it is shown here for the first time that, when several ejectors are used simultaneously, they each retain their performance, without any disturbance of their entrainment ratio or critical outlet pressure. This important new finding paves the way for the design of ERS for variable capacity applications, such as solar cooling systems.

Numerical Investigation on the Effect of Section Width on the Performance of Air Ejector with Rectangular Section

Due to its simple structure and lack of moving parts, the supersonic air ejector has been widely applied in the fields of machinery, aerospace, and energy-saving. The performance of the ejector is influenced by the flow channel structure and the velocity of the jet, thus the confined jet is an important limiting factor for the performance of the supersonic air ejector. In order to investigate the effect of the confined jet on the performance of the ejector, an air ejector with a rectangular section was designed. The effects of the section width (Wc) on the entrainment ratio, velocity distribution, turbulent kinetic energy distribution, Mach number distribution, and vorticity distribution of the rectangular section air ejector were studied numerically. The numerical results indicated that the entrainment ratio of the rectangular section air ejector increased from 0.34 to 0.65 and the increment of the ER was 91.2% when the section width increased from 1 mm to 10 mm. As Wc increased, the region of the turbulent kinetic energy gradually expanded. The energy exchange between the primary fluid and the secondary fluid was mainly in the form of turbulent diffusion in the mixing chamber. In addition to Wc limiting the fluid flow in the rectangular section air ejector, the structure size of the rectangular section air ejector in the XOY plane also had a limiting effect on the internal fluid flow. In the rectangular section air ejector, the streamwise vortices played an important role in the mixing process. The increase of Wc would increase the distribution of the streamwise vortices in the constant-area section. Meanwhile, the distribution of the spanwise vortices would gradually decrease.

Research on similarity characteristics of critical states transferring of adjustable ejector

With ejector technology enters system scale form device scale, the methodology of adjustable ejector has been summarized in the paper. Based on the aerodynamic theory, a performance prediction model for adjustable ejector under variable operating conditions and structures has been presented. Three regulation modes for adjustable ejector have been compared with fixed structure ejector. And results show that adjustable ejector can enlarge the working range of ejector in critical mode. In the ideal qualitative and quantitative combined regulation, adjustable ejector can always work on the peak performance in critical mode with highest entrainment ratio and efficiency. And two special characteristics of “constant capacity” of ejector under different operating conditions and structures have been revealed. A remarkable find is the strong similarity characteristics in critical mode. All critical entrainment ratios converge on curve which is approximately exponential relationship with Critical Expansion Ratio. The Critical Compression Ratio is in linear relation with Critical Expansion Ratio. The critical modes transferring spectrum features of ejector has been presented.

Influence of geometric parameters on the performance of ejector used in aeroengine air system

By using an ejector to draw low-pressure, low-temperature air into the aeroengine's air system, it is possible to significantly enhance the cooling effect of the hot component of the engine. It is very necessary to clarify the sensitivity of ejector performance to different geometric parameters, especially the receiving chamber height, mixing chamber diameter, and diffuser diameter, which are of great significance to improve ejector performance and save limited aeroengine space. Therefore, this paper investigated the effects of these three geometric parameters on the ejector's performance by numerical simulation. The results show that increasing the mixing chamber diameter can significantly improve ejector performance. When the compression ratio is 1.17 and the mixing chamber diameter is increased from 3 mm to 9 mm, the entrainment ratio and the total pressure recovery coefficient are increased by 23.1 % and 7 %, respectively. Especially when the compression ratio is 1, simultaneously increasing the size of the receiving chamber, mixing chamber, and diffuser can greatly improve the ejector's performance. When the diameter of the mixing chamber is increased from 6 mm to 27 mm, the entrainment ratio and the total pressure recovery coefficient are increased by 211 % and 39 %, respectively. The change in ejector structure will influence its flow field and then affect the mixing process. When the size of the ejector is too small, the strong background shock wave suppresses the mixing of the primary flow and the secondary flow, which then causes an increase in the total pressure loss. When the size of the ejector is too large, the eddy current loss leads to ejector performance reduction.

A streamlining method for ejector nozzle profile optimization based on polynomial function

In this study, ejector performance was optimized by streamlining the primary nozzle profile using polynomial functions. Thirteen streamline nozzle profiles with different initial and exit expansion half-angles which determined by quadratic and cubic functions were established, and their performance are discussed. The results indicate that the nozzle profiles designed by cubic function have the best performance than quadratic function. To improve the effective working range, the ejector should have an initial expansion half-angle that is as small as possible and an exit expansion half-angle that is as large as possible. To enhance the entrainment ratio, the ejector should have a constant exit expansion half-angle and a minimum initial expansion half-angle of 1°. An excessive initial expansion half-angle caused a sealed Mach number contour inside the nozzle, which wasted energy to reduce the velocity and increase the static pressure, decreasing the working efficiency of the primary flow. In addition, the entrainment ratio significantly decreased with a large exit expansion half-angle (greater than 17°).

Measurement and Prediction of Droplet Entrainment in Inclined Liquid–Liquid Flow by PLIF Method

Inclined liquid-liquid two-phase flows widely exist in petroleum, chemical, and other important industrial processes. The study of droplet entrainment in inclined flow is of great significance for investigating the heat/mass transfer between phases and optimizing the industrial production processes. In this study, a planar laser-induced fluorescence (PLIF) system is designed to visualize the inclined liquid-liquid flows. The silicone oil (organic phase) and water/glycerol mixture (aqueous phase) are used as the experimental media. The length and amplitude of the interfacial waves are derived from the flow visualizations. The relationship between the critical wavelengths and Froude number is explored to indicate the transition from stratified flow (ST) to stratified flow with mixing at the interface (ST&MI). The wave aspect ratio is derived to characterize the instability and breakage of the interfacial wave. Meanwhile, the entrainment ratios of dispersed droplets in the continuous phases are detected, and the effects of the flow rate and the interfacial shear on the droplet entrainment are studied. Finally, a physical model is developed to predict the droplet entrainment ratios based on the force balance analysis of the interfacial wave. In general, the developed model is effective in predicting the droplet entrainment ratio with mean absolute errors of 0.015 and 0.023 for the organic and aqueous droplets, respectively.

Investigation of Fluid Characteristic and Performance of an Ejector by a Wet Steam Model

In this paper, a wet steam model is utilized to study the fluid characteristic and performance of a supersonic ejector. The condensation process, which has been ignored by most researchers, is analyzed in detail. It is found that the most intensive condensation happens at the primary nozzle downstream and nozzle exit region. Moreover, the impacts of primary flow pressure and back pressure on ejector performance are studied by the distribution of Mach number inside the ejector. Furthermore, the results show that the secondary mass flow rate first grows sightly then remains almost unchanged, while the primary mass flow rate rises sharply and ejector entrainment ratio drops dramatically with the increase in primary flow pressure.

Entrainment Rates and Their Synoptic Dependence on Wind Speed Aloft in California's Central Valley

Daytime atmospheric boundary layer (ABL) dynamics—including potential temperature budgets, water vapour budgets, and entrainment rates—are presented from in situ flight data taken on six afternoons near Fresno in the San Joaquin Valley (SJV) of California during July/August 2016. The flights took place as a part of the California Baseline Ozone Transport Study aimed at investigating transport pathways of air entering the Central Valley from offshore and mixing down to the surface. Midday entrainment velocity estimates ranged from 0.8 to 5.4 cm s−1 and were derived from a combination of continuously determined ABL heights during each flight and model-derived subsidence rates, which averaged -2.0 cm s−1 in the flight region. A strong correlation was found between entrainment velocity (normalized by the convective velocity scale) and an inverse bulk ABL Richardson number, suggesting that wind shear at the ABL top plays a significant role in driving entrainment. Similarly, we found a strong correlation between the entrainment efficiency (the ratio of entrainment to surface heat fluxes with an average of 0.23 ± 0.15) and the wind speed at the ABL top. We explore the synoptic conditions that generate higher winds near the ABL top and propose that warm anomalies in the southern Sierra Nevada mountains promote increased entrainment. Additionally, a method is outlined to estimate turbulence kinetic energy, convective velocity scale (w*), and the surface sensible heat flux in the ABL from a slow, airborne wind measurement system using mixed-layer similarity theory.

Optimization of Three Key Geometries of a Steam Ejector under Varied Primary Nozzle Geometries

In this paper, three key geometrical dimensions such as XL3 (constant pressure mixing chamber length), D5 (diameter of the throat of the ejector), and XL5 (length of the throat of the ejector) were separately or sequentially optimized under different lengths and angles of two sections of the primary nozzle. Furthermore, shock cluster number and shock chain length or area of low static pressure zone were used to analyze the effect of geometries on ejector performance, which is normally indicated by entrainment ratio (ER, or the ratio between the mass flow rate of secondary flow and the mass flow rate of primary flow). The results show that: (1) the improvement of ejector performance with only optimization of the primary nozzle is quite limited, in comparison, the impact of length and angle of nozzle diverging section on ejector performance is higher than that of converging section; (2) the relative sensitivity of ER to three key dimensions is much higher than that to the angles and lengths of the primary nozzle; (3) with the increase of XL3 and D5, ER needs a larger angle and smaller length of nozzle converging section; (4) the impact of key geometries on ejector performance can be analyzed with the help of shock cluster number and shock chain length or area of low static pressure zone.

Optimal technical analysis of vacuum ejector for passive hydrogen recovery

In this study, the numerical analysis and experimental measurements are conducted on the internal flow field and temperature distribution of ejectors with different throat diameters. The computational fluid dynamics (CFD) is used to simulate different ejectors and investigate the effects of Mach number, pressure, and temperature distributions. The hydrogen Entrainment Ratio (ER) of ejectors is also measured for proton exchange membrane fuel cell applications. The experimental measurements and simulations of the hydrogen Entrainment Ratio of the ejectors showed that the recovery efficiencies are 59%, 53%, and 33% for the pipe diameters of 0.5, 0.7, and 1.0 mm at the inlet pressures of 340 kPa, respectively. In different area ratios, the larger area ratio of the nozzle leads to greater difference between the diameter of the throat and the diameter of the throat outlet. This causes a smaller recovery rate. In the internal flow field of the ejector, higher recovery rate can be achieved by using the closer location of the positive shock wave to the nozzle outlet.

High performance ejector enhanced by heat exchanger in solid oxide fuel cell anode recirculation system

The ejector-based recirculation system has a promising application in the solid oxide fuel cell (SOFC) with the advantages of no parasitic power, small size, lightweight, and easy maintenance compared with the pump-driven system. However, it is difficult for the ejector to satisfy the requirements of high backpressure and the high-entrainment ratio at the same time in the SOFC system. To overcome the problems, a heat exchanger enhanced SOFC anode recirculation system is proposed for improving the performance of the ejector whose primary flow is heated by the second flow through a heat exchanger in the high-pressure ratio of 1.08. The flow characteristic and performance of the ejector are investigated with the variation of the inlet temperatures by computer fluid dynamics (CFD) and the experiment. The results show that the entrainment ratio ω and the steam to carbon ratio (STCR) are improved respectively from 2.37 to 7.73 and 0.74 to 2.11 at the pressure ratio of 1.08 compared with the condition without the heat transfer. Meanwhile, the current density and power of the SOFC are increased from 414.68 A/m2 to 552.20 A/m2 and 34.84 kW to 45.88 kW, and the voltage of the SOFC has practically maintained at 0.88 V. The improvement of the SOFC power is up to 30 %. The exchanger enhanced ejector recirculation system provides an effective way for improving the performance of the SOFC system.

Design and Investigation of a Dynamic Auto-Adjusting Ejector for the MED-TVC Desalination System Driven by Solar Energy.

Ejectors have been widely used in multi-effect distillation, thermal vapor compression (MED-TVC) desalination systems due to their simple structures and low energy consumption. However, traditional fixed geometry ejectors fail to operate under unstable working conditions driven by solar energy. Herein, a dynamic auto-adjusting ejector, equipped with a needle at the nozzle throat, is proposed to improve the ejector's performance under changeable operating conditions. A two-dimensional computational fluid dynamics (CFD) model is built to analyze the performance and flow field of the ejector. It is found that the achievable entrainment ratio gradually increases as the needle approaches the nozzle, and the entrainment ratio of the ejector is relatively stable, varying slightly between 1.1-1.2 when the primary pressure changes from 2.5 to 4 bar. Besides, the performance comparison between the proposed ejector and the traditional ejector is studied under the same primary pressure range. The entrainment ratio of the designed ejector was 1.6 times higher than that of the conventional ejector at a primary pressure of 2.5 bar. Furthermore, the average entrainment ratio of the designed ejector is 1.14, as compared to 0.84 for the traditional ejector. Overall, the proposed auto-adjusting ejector could be potentially used in MED-TVC desalination systems under variable conditions.