Performance analysis of lobed nozzle ejectors for high altitude simulation of rocket engines

Ejectors are used in high altitude testing of rocket engines to create vacuum for simulat-ing the engine test in vacuum conditions.The performance of an ejector plays a vital role in creating vacuum at the exit of the engine nozzle and the nozzle design exit pressure at the time of ignition.Consequently,the performance of ejectors has to be improved to reduce the consumption of active fluid.In this investigation,the performance of an ejector has been improved by changing the exit shear plane of the nozzle.Conventionally,conical nozzles are used for creating the required momentum.Lobes of 4 no’s,6 no’s and 8 numbers for an equivalent area ratio=5.88 are used to increase the shear area.The influence of shear plane variation in the suction pressure is studied by a detailed CFD analysis.

Design and simulation of gas burner ejectors

Ignition within gas burner ejectors can lead to off design conditions and has significant influence on the burner behavior.Thus ignition in the ejector should be prevented.In the present study the influence of combustion reactions on the performance of gas burner injectors is investigated.To investigate if ignition is possible,simulated ignition delay times,using a detailed reaction mechanism,are compared to predicted mean residence times of the gas in the ejector.Gas burner ejectors are designed using one dimensional analytic equations,based on energy and momentum conservation equations and conventional isentropic equations.1D results are compared to 2D computational fluid dynamics(CFD)simulations,to take into account non-ideal mixing effects along the ejector.Results are validated with experiments with air at room temperature.1D results show very good agreement not only with CFD simulations for the case of non-reactive flows,but also with performed experiments.It is shown that the assumption of ideal mixing along the ejector and thus the comparison of the ignition delay time to the gas mean residence time,to predict ignition in the ejector,is not valid.Ignition in the ejector is possible,even if the ignition delay time is more than thirty times higher than the mean residence time.In addition to that,it is shown,that ignition and the choice of reaction mechanism have significant influence on the predicted gas burner ejector performance.Thus,the accurate prediction of ignition delay time and the use of a detailed reaction kinetic are mandatory to correctly predict the burner ejector behavior.

Effect of an Internal Heat Exchanger on the Performances of a Double Evaporator Ejector Refrigeration Cycle

A theoretical investigation is presented about a double evaporator ejector refrigeration cycle(DEERC).Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by an internal heat exchanger(IHX).The ejector is introduced into the baseline cycle in order to mitigate the throttling process losses and increase the compressor suction pressure.Moreover,the IHX has the structure of a concentric counter-flow type heat exchanger and is intentionally used to ensure that the fluid at the compressor inlet is vapor.To assess accurately the influence of the IHX on the DEERC performance,a mathematical model is derived in the frame of the dominant one-dimensional theory for ejectors.The model also accounts for the friction effect in the ejector mixing section.The equations of this model are solved using an Engineering Equation Solver(EES)for different fluids.These are:R134a as baseline fluid and other environment friendly refrigerants used for comparison,namely,R1234yf,R1234ze,R600,R600a,R290,R717 and R1270.The simulation results show that the DEERC with an IHX can achieve COP(the coefficient of performance)improvements from 5.2 until 10%.

THERMAL CALCULATION FOR ANTI-ICERWITH MICRO-EJECTOR

The anti-icer with micro-ejector is used in Y7 wing thermal anti-icingsystem to save the used air. Thermal calculation for this type of icer is very importantfor design of the anti-icing system. The calculation of the icer is descnbed. The]nathcinatical m

几种新型手枪射击弹壳上痕迹特征浅析

为了适应新形势下枪弹检验工作的需要,我中心枪弹处于1997、1998年分别购置了一批新型枪支.其中有13种配用9mm×19mm巴拉贝鲁姆手枪弹的新型手枪,它们分别是213型9毫米手枪、213A型9毫米手枪、七七B型9毫米手枪、七七B2型9毫米手枪、NP20型9毫米手枪、NP22型9毫米手枪、NP28型9毫米手枪、NP38型9毫米手枪、201C型9毫米手枪和NZ75型9毫米手枪.为了让更多的同行了解这13种新型手枪发射子弹的弹壳上的主要痕迹特征,我们制作了一些样本.由于每种枪仅购置了一支,故本文所介绍的有些痕迹特征究竟属于种类特征,抑或是个别特征,还有待于作进一步的实验和研究.将13种枪支划分为5组分别进行论述:一组:213型、213A型;

Sewerage Force Adjustment Technology for Energy Conservation in Vacuum Sanitation Systems

The vacuum sanitation is the safe and sound disposal approach of human excreta under the specific environments like flights, high speed trains and submarines. However, the propulsive force of current systems is not adjustable and the energy consumption does not adapt to the real time sewerage requirement. Therefore, it is important to study the sewerage force adjustment to improve the energy efficiency. This paper proposes an energy conservation design in vacuum sanitation systems with pneumatic ejector circuits. The sewerage force is controlled by changing the systematic vacuum degree according to the amount of the excreta. In particular, the amount of the excreta is tested by liquid level sensor and mass sensor. According to the amount of the excreta, the relationship between the excreta amount and the sewerage force is studied to provide proper propulsive force. In the other aspect, to provide variable vacuum degrees for different sanitation requirements, the suction and discharge system is designed with pneumatic vacuum ejector. On the basis of the static flow-rate characteristics and the vacuum generation model, the pressure response in the ejector circuit is studied by using the static flow rate characteristics of the ejector and air status equation. The relationship is obtained between supplied compressed air and systematic vacuum degree. When the compressed air is supplied to the ejector continuously, the systematic vacuum degree increases until the vacuum degree reaches the extreme value. Therefore, the variable systematic vacuum degree is obtained by controlling the compressed air supply of the ejector. To verify the effect of energy conservation, experiments are carried out in the artificial excreta collection, and the variable vacuum-degree design saves more than 30% of the energy supply. The energy conservation is realized effectively in the new vacuum sanitation systems with good application prospect. The proposed technology provides technological support for the energy conservation of vacuum sanitation systems.

Numerical Study on Flow-Induced Vibration of Ejector Structure

High-speed airflow in wind tunnel tests usually causes dramatic vibration of ejector structure,which may lead to fatigue and even destruction of the wind tunnel.Therefore,analyzing and solving the flow-induced vibration problem is a tough and indispensable part of the wind tunnel security design.In this paper,taking a kind of two-stage ejector as the study object,multiple numerical simulation methods are adopted in order to carry out research on the analysis technique of the flow-induced vibration characteristics of ejector structure.Firstly,the structural dynamics characteristic is analyzed by using the ejector structural dynamics numerical model,which is built on the basis of finite element method.Secondly,the complex flow phenomenon is explored applying numerical fluid-dynamics model of the inner flow field of the ejector,which is constructed on the basis of finite volume method.Finally,based on the two numerical models above,the vibration response of the ejector structure induced by the high-speed airflow is computed via the fluid-solid coupling technique.The comparison of the simulation results with the actual vibration test indicates that these numerical simulation methods can accurately figure out the rule of flow-induced vibration of ejectors.

Performance Analysis of an Organic Rankine Cycle with a Preheated Ejector

The so-called organic Rankine cycle(ORC)is an effective technology allowing heat recovery from lower temperature sources.In the present study,to improve its thermal efficiency,a preheated ejector using exhaust steam coming from the expander is integrated in the cycle(EPORC).Considering net power output,pump power,and thermal efficiency,the proposed system is compared with the basic ORC.The influence of the ejector ratio(ER)of the preheated ejector on the system performances is also investigated.Results show that the net power output of the EPORC is higher than that of the basic ORC due to the decreasing pump power.Under given working conditions,the average thermal efficiency of EPORC is 29%higher than that of ORC.The ER has a great impact on the performance of EPORC by adjusting the working fluid fed to the pump,leading to significant variations of the pump work Moreover,the ER has a remarkable effect on the working fluid temperature lift(TL)at the evaporator inlet,thus reducing the evaporator heat load.According to the results,the thermal efficiency of EPORC increases by 30%,when the ER increases from 0.05 to 0.4.

Thermodynamic Investigation of a Solar Energy Cogeneration Plant Using an Organic Rankine Cycle in Supercritical Conditions

In the present work,a novel Organic Rankine Cycle(ORC)configuration is used for a low-grade heat source cogeneration plant.An investigation is conducted accordingly into the simultaneous production of electricity and cold.The proposed configuration relies on concentrated solar power(as heat source)and ambient air(for cooling).Furthermore,two gas ejectors are added to the system in order to optimize the thermodynamic efficiency of the organic Rankine cycle.The results show that the thermodynamic and geometric parameters related to these ejectors have an important effect on the overall system performances.In order to account for the related environmental impact,the following working fluids are considered:HCFC-124,HFC-236fa,HFO-1234yf and HFO-1234ze.As shown by the numerical simulations,the fluid R1234yf presents the minimal heat consumption and therefore provides an optimal thermal efficiency for the ORC cycle(which is around 29%).However,the refrigerant R236fa displays the highest refrigeration performances with a performance coefficient reaching a value as high as 0.38.

Performance Improvement of Two-Phase Steam Ejector based on CFD Techniques,Response Surface Methodology and Genetic Algorithm

The steam ejector is a crucial component in the waste heat recovery system.Its performance determines the amount of recovered heat and system efficiency.However,poor ejector performance has always been the main bottleneck for system applications.Therefore,this study proposes an optimization methodology to improve the steam ejector's performance by utilizing computational fluid dynamics(CFD) techniques,response surface methodology(RSM),and genetic algorithm(GA).Firstly,a homogeneous equilibrium model(HEM) was established to simulate the two-phase flow in the steam ejector.Then,the orthogonal test was presented to the screening of the key decision variables that have a significant impact on the entrainment ratio(ER).Next,the RSM was used to fit a response surface regression model(RSRM).Meanwhile,the effect of the interaction of geometric parameters on the performance of the steam ejector was revealed.Finally,GA was employed to solve the RSRM's global optimal ER value.The results show that the RSRM exhibits a good fit for ER(R^(2)=0.997).After RSM and GA optimization,the maximum ejector efficiency is 27.94%,which is 48.38% higher than the initial ejector of 18.83%.Furthermore,the optimized ejector efficiency is increased by 46.4% on average under off-design conditions.Overall,the results reveal that the combination of CFD,RSM,and GA presents excellent reliability and feasibility in the optimization design of a two-phase steam ejector.

Experimental and Numerical Research on Strengthening the Performance of Wave Rotor Equipment with Curved Passages

The wave rotor technology is an energy exchanging approach that achieves efficient energy transfer between gases without using mechanical components.The wave rotor technology has been successfully utilized in gas turbine cycle systems,gas expansion refrigeration and a variety of other industrial domains,yielding numerous researches and application outcomes.The structure of wave rotor passages inside which the energy exchange between gases is realized has an important impact on the equipment performance.In this study,based on gas wave ejection technology,the first application trials of an expansion wave rotor with curved passages were conducted.Additionally,the performance enhancing effect and mechanism of curved passages on the energy exchanging process were studied precisely by the combination of experimental and three-dimensional numerical simulation methods.The experimental results demonstrate that the curved passage rotor(CIR rotor)employed in this research has a maximum isentropic efficiency of 61.6%,and the CIR rotor achieves higher efficiency than the straight passage rotor(STR rotor)on all working conditions in this study.Compared with the STR rotor,the maximum efficiency improving ratio of CIR rotor can exceed 14.2%at each experimental expansion ratio,and the maximum relative increments of ejection rate are more than 5%.In addition,the CIR rotor can also effectively increase the proportion of static pressure in total pressure of the medium-pressure gas,and reduce the device power consumption.The three-dimensional numerical investigations revealed the principle of gas ejection in the wave rotors and explained why the CIR rotor performed better.According to the numerical findings,the curved passages of the CIR rotor may effectively minimize various energy losses created in the processes of high-pressure gas incidence,exhausting flow in nozzle,and high-speed gas flow in the passages.

Review of enhancement for ocean thermal energy conversion system

Ocean thermal energy conversion(OTEC)is a renewable energy source that uses differences in ocean water temperature between warm surface and cold depth to generate electricity.It is an essential link in the carbon neutrality chain and one of the rising sectors of the ocean energy.This paper provides an overview of studies on closed thermodynamic cycles and the numerous difficulties that OTEC technology faces.A description of the thermodynamic cycles incorporating mixed or pure working fluids,as well as the implications of different working fluids on cycle efficiency were also studied.Changes in condensing and evaporating temperatures induced by variations in heat resources affect the efficiency of cycles with pure working fluids.Several strategies,such as intermediate extraction regeneration and heat recovery of ammonia-depleted solution can increase the thermal efficiency with mixed working fluids.In addition,the impact of the ejector on the cycle’s performance is examined.Finally,the efficiency-improving strate-gies are described and summarized.Thermodynamic efficiency can increase using suitable working fluids and taking steps to maximize the rate of ocean thermal energy.To establish which approach is the most effective,different methods have been evaluated and compared under identical operating conditions.

EXPERIMENTAL STUDY ON THE EFFECTS OF AIR ENTRAINMENT ON A PLANE JET DIFFUSION IN A PLUNGE POOL

Laboratory experimental results about the effects of air entrainment on the jet diffusion in a plunge pool were presented. The results indicate that the air entrainment has little effect on the maximum mean impinging pressure generated by the jet at pool bottom. The maximum fluctuating pressure is increased with the increase of the air entrainment. Air entrainment also reduces jet spreading.

Thermodynamic Analysis of a Modified Ejector-Expansion Refrigeration Cycle with Hot Vapor Bypass

In this study,a modified ejector-expansion refrigeration cycle(MERC)is proposed for applications in small refrigeration units.A vapor bypass circuit is introduced into the standard ejector expansion refrigeration cycle(ERC)for increasing the ejector pressure lift ratio,thereby lowering the compressor pressure ratio in the MERC.A mathematical model has been established to evaluate the performances of MERC.Analysis results indicate that since a two phase vapor-liquid stream is used to drive the ejector in the MERC,a larger ejector pressure lift ratio can be achieved.Thus,the compressor pressure ratio decreases by 21.1%and the discharge temperature reduces from 93.6℃to 82.1℃ at the evaporating temperature of-55℃ when the vapor quality of two phase vapor-liquid stream increases from 0 to 0.2.In addition,the results show that the higher ejector component efficiencies are effective to reduce the compressor pressure ratio and the discharge temperature.Actually,the discharge temperature reduces from 91.4℃ to 82.1℃ with the ejector component efficiencies increasing from 0.75 to 0.85 at the two phase stream vapor quality of 0.2.Overall,the proposed cycle is found to be feasible in lower evaporating temperature cases.

Air-source heat pump coupled with economized vapor injection scroll compressor and ejector:Design and experimental research

Ejector can utilize high pressure energy from liquid mechanism,it can be used in heat pump system coupled with economized vapor injection(EVI)scroll compressor.When running under low temperature conditions,the performance of the EVI system with ejector can be improved further.In this paper,the design method of the heat pump system with ejector is presented,and the process for designing the heat pump with ejector(EVIe)was summarized.One prototype heat pump was designed under the condition of the evaporation temperature of -20oC,and an experimental setup was established to test the prototype.The measured results demonstrated that the heating EER(energy efficiency ratio)of the EVIe could reach about 4%higher than that of the system without the ejector when the heating capacity remained nearly constant.The design method is helpful to development of a heat pump system coupled with scroll compressor and ejector.

Experimental evaluation of the effect of an internal heat exchanger on a transcritical CO_2 ejector system

This study presents experimental results focused on a performance comparison of a transcritical CO2 ejector system without an internal heat exchanger(IHX) (EJE-S) to a transcritical CO2 ejector system with an IHX(EJE-IHX-S) . The comparison includes the effects of changes in operating conditions such as cooling water flow rate and inlet temperature. Experiments are conducted to assess the influence of the IHX on the heating coefficient of performance(COPr) ,heating capacity,entrainment ratio,pressure lift,and other parameters. The primary flow rate of the EJE-IHX-S is higher than that of the EJE-S. The pressure lift and actual ejector work recovery are reduced when the IHX is added to the transcritical CO2 ejector system. Using a more practical performance calculation,the compression ratio in the EJE-S is reduced by 10.0%-12.1%,while that of EJE-IHX-S is reduced only by 5.6%-6.7% compared to that of a conventional transcritical CO2 system. Experimental results are used to validate the findings that the IHX weakens the contribution of the ejector to the system performance.

Prospect Evaluation of Low-GWP Refrigerants R1233zd(E)and R1336mzz(Z)Used in Solar-Driven Ejector-Vapor Compression Hybrid Refrigeration System

In this paper,the entrainment ratio,pump work,heat loads of heat exchangers and COPthermal were theoretically evaluated for a solar-driven ejector-vapor compression hybrid refrigeration system with R1233zd(E)and R1336mzz(Z)as the working fluids.The evaluation of the utilization potentials of R1233zd(E)and R1336mzz(Z)was presented by comparing the system performance with that of R245fa,a commonly used refrigerant in the ejector system.The results indicated that the systems with R1233zd(E)and R1336mzz(Z)had a higher entrainment ratio and lower pump work.The pump works when using R1233zd(E)and R1336mzz(Z)can be up to 14.59%and 38.05%lower than those of R245fa,respectively.Meanwhile,the system showed the highest COPthermal utilizing R1233zd(E)followed by that of R245fa,with the R1336mzz(Z)system having the lowest value.The differences between R1233zd(E)and R1336mzz(Z)systems,R1233zd(E)and R245fa systems were 4.33%and 2.0%,respectively.This paper was expected to provide a good reference for the utilizing prospect of R1233zd(E)and R1336mzz(Z)in ejector refrigeration systems.

Performance Analysis of an Ejector Enhanced Two-Stage Auto-Cascade Refrigeration Cycle for Low Temperature Freezer

In this paper,an ejector enhanced two-stage auto-cascade refrigeration cycle(EARC)using ternary mixture R600a/R32/R1150 is proposed for application of-80℃freezing.In EARC cycle,an ejector was employed to recover the expansion work in the throttling processes and lifted the suction pressure of the compressor.The performances of the ejector enhanced two-stage auto-cascade refrigeration cycle and conventional auto-cascade refrigeration cycle(CARC)were compared using thermodynamic analysis methods.The influences of the important operation parameters including mass fraction ratio of the mixture,fluid quality at the second separator inlet,condensation temperature,evaporation temperature,and expansion ratio of expansion valve on the performances of EARC cycle were discussed in detail.The results indicate that ternary mixture R600a/R32/R1150 has the optimal mass fraction ratio of 0.45/0.2/0.35 with respect to the maximum COP.The EARC cycle yields higher performance than the CARC cycle in terms of COP,exergy efficiency and volumetric refrigeration capacity.And 4.9%-36.5%improvement in COP and 6.9%-34.3%higher exergy efficiency could be obtained in EARC cycle comparing with CARC cycle.The finding of this study suggests that the EARC cycle has a promising application potential for low temperature freezing.

Investigation of Vapor-liquid Ejector with Organic Working Fluids

The vapor-liquid ejector is a simply flow device and driven by thermal energy. In this paper, a modified mathematical model of the vapor-liquid ejector is proposed, and the validation shows good agreements with the experimental data. A study is carried out with six organic working fluids, namely R1233 zd(E), R1336 mzz(Z), R236 ea, R245 ca, R245 fa and R365 mfc. The influences of the entrainment ratio, the area ratio, the superheating at the vapor nozzle inlet, the subcooling at the liquid nozzle inlet, and the pressures at these inlets on the pressure lifting are parametrically investigated. An increase in the subcooling leads to the great increasing of pressure lifting and the superheating has slight effect on the pressure lifting, whereas others have the opposite tendency. The studies of the pressures and temperatures at the typical locations inside the vapor-liquid ejector are further conducted by using R1336 mzz(Z). The results show that the above parameters have great influence on these pressures and temperatures inside except that the pressures are insignificantly impacted by the superheating, and the temperatures are negligibly affected by the area ratio. R1336 mzz(Z) is recommended as a good working fluid for the vapor-liquid ejector.

Experimental Investigation of the Ejector Refrigeration Cycle for Cascade System Application

Ejector refrigeration cycle(ERC)with advantages of simple structure and low cost holds great application potential in cascade/hybrid cycles to improve the overall system performance by removing or recovering the heat from the main cycle.In this paper,a theoretical and experimental investigation of the ERC as a part of a cascade system was carried out.The operating parameters were optimized.The experimental ERC test rig was designed,developed and investigated at high evaporating temperatures and wide ranges of operating conditions.The influence of operating conditions on the efficiency of the ejector and ERC was analyzed.Experimental results and analysis in this study can be helpful for the application and operating condition optimization of ERC in cascade/hybrid refrigeration systems.