Nozzle Exit Position Research Articles

1-D model for finding geometry of a single phase ejector

This paper presents a novel 1-D mathematical model to determine complete dimensions of an ejector component of Ejector Refrigeration System (ERS). The concepts of Prandtl's mixing length, Prandtl-Meyer expansion wave, Kelvin-Helmholtz instability and Baroclinic effect are introduced in the model to precisely determine the various diameters, mixing length, nozzle exit position etc. for the given conditions of the primary & secondary fluid, cooling capacity and critical condenser pressure. The area ratios obtained using the mathematical model are compared with the experimental/numerical results available in open literature for the same operating conditions and are found to be in good agreement. Moreover, ejector geometry determined from the proposed model is analyzed using CFD for the same input conditions. Average deviation in the entrainment ratio obtained using CFD and that given to the model is found to be less than 2.48% and thus model is validated again. The experimental test rig of ejector refrigeration system is also fabricated and the performance is evaluated while operating at critical condenser pressure. The deviation in the ejector geometry used in the experiment is found to be less than 7% in comparison to the ejector dimensions calculated by the numerical model for the same input conditions.

Experimental parametric investigation of vapor ejector for refrigeration applications

A prototype ejector system having a nominal cooling capacity of 30 kW was used to study the influence of ejector geometry and operating conditions on the ejector performance. Experiments were realized over a wide parameter range: primary inlet pressure from 1700 to 2900 kPa; secondary inlet pressure from 170 to 550 kPa; outlet pressure from 350 to 1000 kPa. The performance was evaluated in terms of the entrainment ratio and the temperature lift. The experimental results led to the following observations: (a) A simple calculation of the primary mass flow rate can be used for the design of ejector systems; (b) A given ejector operated at fixed primary inlet pressure shows a range of outlet pressures where the entrainment ratio is maximum. A correlation of the optimal entrainment ratio versus the primary pressure is proposed; (c) There is an inverse relationship between the temperature lift and the entrainment ratio; (d) For a fixed primary inlet pressure, the optimal outlet pressure can be set at a given value by the appropriate geometry of the ejector. Finally, a two-plateau behavior of entrainment ratio as a function of outlet pressure was observed, which might be related to an improper nozzle exit position.

Experimental and numerical investigations on the effect of suction chamber angle and nozzle exit position of a steam-jet ejector

Implementation of renewable energy in existing applications has become an emerging trend in order to mitigate the environmental issues. Specifically, HVAC sector urges for more efficient and eco-friendly systems which can effectively replace the high grade energy in conventional systems. One of such promising environmental friendly systems is the ejector refrigeration system which has low initial and operating costs, simple system components and trouble free operation. In spite of these merits, it suffers from low performance due to the complex irreversible fluid flow prevailing in the ejector. Comprehensive analysis and understanding of all the geometrical and operating parameters governing the ejector flow are vital for increasing the performance of the entire system. In this study, the most crucial geometrical parameters such as suction chamber angle and the Nozzle Exit Position (NXP) of a steam operated ejector are systematically investigated using CFD and experimental techniques. The influence of operating conditions with respect to the geometrical parameters has been observed, and for the tested conditions of 700 W evaporator at 10 °C cooling temperature the suction chamber angle of 12° and the corresponding NXP of 24.7 mm delivered an optimum performance for the active and back pressures of 2 bar and 43 mbar respectively.

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).

Auto-tuning ejector for refrigeration system

In this paper, an auto-tuning AR (area ratio) ejector and an auto-tuning NXP (nozzle exit position) ejector are designed to solve the contradictions between the fixed structure and the dynamic primary pressure driven by multi-condition low-grade heat energy. A CFD (Computational Fluid Dynamics) model is used to calculate the performance of the ejector under different operational conditions. The effects of both AR and NXP on the performance of the ejector are systematically studied. The optimal area ratio increases linearly along with the primary pressure, and the optimum NXP decreases as the primary flow pressure increases. Following this, auto-tuning AR and NXP ejectors are designed to enhance the performance of the ejector by self-adjusting the AR and NXP with a variation in primary flow pressure. Simulation results show that the auto-tuning ejector has a strong ability to improve the ejector performance compared with the constant structure ejector.

Performance evaluation and parametric studies on variable nozzle ejector using R134A

Computational fluid dynamics of variable nozzle ejector has been studied to determine the optimum nozzle exit position for reliable ejector cooling cycle operations. The flow rates of primary and secondary stream were varied to obtain the optimum entrainment ratio under different ranges of operating conditions.The refrigerant R134a was chosen based on the merit of its environmental and performance characteristics, the refrigerant was chosen because currently is used widely in air conditioning system. It was found that the computational fluid dynamics showed that the optimum positioning of nozzle exit position, which was based on the parameters such as pressure inlet variation the temperature inlet. The results obtained after the optimization of the results showed that the optimum nozzle exit position was found at 3 mm from the mixing chamber inlet when the operating conditions pressure inlet, secondary pressure inlet, primary temperature inlet and outlet pressure were at (18bar,6bar,373K,and5.6bar) respectively. Similarly, the range of entrainment ratio was varied between 0.24−1.283 at a constant area ratio, and at varied operating conditions.

Ejectors of power plants turbine units efficiency and reliability increasing

The functioning of steam turbines condensation systems influence on the efficiency and reliability of a power plant a lot. At the same time, the condensation system operating is provided by basic ejectors, which maintain the vacuum level in the condenser. Development of methods of efficiency and reliability increasing for ejector functioning is an actual problem of up-to-date power engineering.In the paper there is presented statistical analysis of ejector breakdowns, revealed during repairing processes, the influence of such damages on the steam turbine operating reliability. It is determined, that 3% of steam turbine equipment breakdowns are the ejector breakdowns. At the same time, about 7% of turbine breakdowns are caused by different ejector malfunctions. Developed and approved design solutions, which can increase the ejector functioning indexes, are presented. Intercoolers are designed in separated cases, so the air-steam mixture can’t move from the high-pressure zones to the low-pressure zones and the maintainability of the apparatuses is increased. By U-type tubes application, the thermal expansion effect of intercooler tubes is compensated and the heat-transfer area is increased. By the applied nozzle fixing construction, it is possible to change the distance between a nozzle and a mixing chamber (nozzle exit position) for operating performance optimization.In operating conditions there are provided experimental researches of more than 30 serial ejectors and also high-efficient 3-staged ejector EPO-3-80, designed by authors. The measurement scheme of the designed ejector includes 21 indicator. The results of experimental tests with different nozzle exit positions of the ejector EPO-3-80 stream devices are presented. The pressure of primary stream (water steam) is optimized. Experimental data are well-approved by the calculation results.

Design and numerical investigation of an adaptive nozzle exit position ejector in multi-effect distillation desalination system

Few investigations have been conducted on an ejector that has an auto-tuning capability to regulate the performance of a multi-effect distillation-thermal vapour compression (MED-TVC) desalination system with the variation of operating conditions. In this study, an adaptive nozzle exit position (ANXP) ejector was first proposed to enhance ejector performance by self-adjusting the position of the primary nozzle with the change of primary pressure. A computational fluid dynamics (CFD) model was established and validated using experimental data. Simulation results indicate that there is an optimum NXP range of 43 mm–70 mm for an ejector to achieve its highest performance. The maximum increase of the entrainment ratio is 35.8% compared to that at an NXP of −30 mm. The secondary flow rate first increases and then decreases while the primary flow rate remains unchanged with the increase of the NXP in fixed working conditions. Furthermore, a correlation between optimum NXP and primary pressure was developed to provide designing parameters for the ANXP ejector.

Numerical Investigation of Miniature Ejector Refrigeration System Embedded with a Capillary Pump Loop.

A miniature steam ejector refrigeration system embedded with a capillary pump loop can result in a compact design which can be used for electronics cooling. In this paper, computational fluid dynamics (CFD) is employed to investigate the effects of the area ratio of the ejector constant-area mixing section to the nozzle throat, the length of the constant-area section, and the nozzle exit position (NXP), on the performance of a miniature steam ejector. Results show that the performance of the miniature steam ejector is very sensitive to the area ratio of the constant-area mixing section to the nozzle. For the needs of practical application, the area ratio of the constant-area mixing section to the nozzle should be smaller than 16 when the temperature of the primary flow is 60 °C. The NXP plays an important role in the flow phenomena inside the miniature ejector. The critical back pressure is more sensitive to length of the constant-area mixing section than the entrainment ratio. Results of this investigation provided a good solution to the miniature steam ejector embedded with a capillary pump loop for electronics cooling application.

Experimental investigation on low-temperature thermal energy driven steam ejector refrigeration system for cooling application

In recent years, ejector refrigeration has been a hot topic for research because it can utilize low-grade energy such as solar energy or industrial waste heat. Even more importantly, it uses the most environmentally friendly substance, water, as the working fluid. According to the literatures, the utilization of the thermal energy from a low-temperature heat source below 80°C is a considerable challenge for the steam ejector refrigeration system. In this paper, an experimental prototype of the steam ejector refrigeration system was designed and built up. Three ejectors with a same nozzle for the primary nozzle and three different constant-area sections were designed and fabricated. The effects of the operating temperatures, the nozzle exit position (NXP) and the area ratio of the ejector (AR) on the working performance of the steam ejector were investigated. The generating temperature is ranged from 40°C to 70°C. The experimental results show that a steam ejector can operate successfully for a certain configuration size of the steam ejector with a generating temperature ranging from 40°C to 70°C and an evaporating temperature of 15°C. The results of this investigation provided a better understanding for the cooling application of the steam ejector refrigeration system powered by low-temperature heat source. It demonstrates that the steam ejector refrigeration system is a very promising alternative to the absorption refrigeration system, when the heat source temperature is lower than 80°C.

An experimental investigation of steam ejector refrigeration system powered by extra low temperature heat source

A steam ejector refrigeration system is a low capital cost solution for utilizing industrial waste heat or solar energy. When the heat source temperature is lower than 80°C, the utilization of the thermal energy from such a low-temperature heat source can be a considerable challenge. In this investigation, an experimental prototype for the steam ejector refrigeration system was designed and manufactured, which can operate using extra low-temperature heat source below 80°C. The effects of the operation temperature, the nozzle exit position (NXP) and the diameter of the constant area section on the working performance of the steam ejector were investigated at generating temperatures ranging from 40°C to 70°C. Three ejectors with a same de Laval nozzle for the primary nozzle and three different constant-area sections were designed and fabricated. The experimental results show that a steam ejector can function for a certain configuration size of the steam ejector with a generating temperature ranging from 40°C to 70°C and an evaporating temperature of 10°C. For a given NXP, the system COP and cooling capacity of the steam ejector decreased until inoperative as the diameter of the constant area section reduced. The results of this investigation provided a good solution for the refrigeration application of the steam ejector refrigeration system powered by an extra low-temperature heat source.

Analytical and Numerical Studies of a Steam Ejector on the Effect of Nozzle Exit Position and Suction Chamber Angle to Fluid Flow and System Performance

Analytical and Numerical Studies of a Steam Ejector on the Effect of Nozzle Exit Position and Suction Chamber Angle to Fluid Flow and System Performance

Experimental study on key geometric parameters of an R134A ejector cooling system

Ejector geometric parameters largely depend on condensation pressure of working fluids. The area ratio of the ejector is much smaller than that of ejector cooling systems using lower condensation pressure working fluids when R134A is used as working fluid. Consequently, it deserves to study other key geometric parameters when using this working fluid. In this paper, the ejector cooling system with R134A was established first. Next, the influence of three geometric parameters such as nozzle exit position, the length of constant-area section and diverging angle of primary nozzle on the ejector performances was investigated via experimental methods. The results showed that the influence of nozzle exit position on ejector performance is evident as compared to the other two. Moreover, optimal geometric parameters and dimensionless parameters between them were obtained and compared to those of lower condensation pressure systems. This provided simple but practical ejector design guidelines for real engineering applications.

An experimental study and 1-D analysis of an ejector with a movable primary nozzle that operates with R236fa

The nozzle exit position is an important structural parameter of an ejector. Research shows that movable primary nozzle enhances performance of ejectors. The present work experimentally studied the critical entrainment ratios of an ejector at different nozzle positions, finding that the critical entrainment ratio first increases with the nozzle exit position and then remains constant. A 1-D model proposed to explain this phenomenon found that in a certain range, the critical entrainment ratio is determined by choking of the secondary flow in the converging cone. When the nozzle moves upstream, the mixed flow reaches sound speed at the constant area section, and the critical entrainment ratio remains unchanged.

Development and Performance of an Advanced Ejector Cooling System for a Sustainable Built Environment

Ejector refrigeration is a promising technology for the integration into solar driven cooling systems because of its relative simplicity and low initial cost. The major drawback of such a system is associated to its relatively low coefficient of performance (COP) under variable operating conditions. In order to overcome this problem, an advanced ejector was developed that changes its geometrical features depending on the upstream and downstream conditions. This paper provides a short overview of the development process and results of a small cooling capacity (1.5 kW) solar driven cooling system using a variable geometry ejector. During the design steps, a number of theoretical works have been carried out, including the selection of the working fluid, the determination of the geometrical requirements and prototype design. Based on the analysis, R600a was selected as working fluid. A prototype was constructed with two independent variable geometrical factors: the area ratio and the nozzle exit position. A test rig was also assembled in order to test the ejector performance under controlled laboratory conditions and to elaborate a control algorithm for the variable geometry. Ejector performance was assessed by calculation of cooling cycle COP, entrainment ratio and critical back pressure. The results show that for a condenser pressure of 3 bar, an 80% increase in the COP was obtained when compared to the performance of a fixed geometry ejector. Experimental COP values varied between 0.4 and 0.8, depending on operating conditions. Currently the cooling cycle is being integrated into a solar driven demonstration site for long term “in situ” assessment.

CFD Analysis of Nozzle Exit Position Effect in Ejector Gas Removal System in Geothermal Power Plant

The single stage ejector is used to extract the Non CondensableGas (NCG) in the condenser using the working principle of the Venturi tube. Three dimensional computational simulation of the ejector according to the operating conditions was conducted to determine the flow in the ejector. Motive steam entering through the convergent – divergent nozzle with increasing flow velocity so that the low pressure exist around the nozzle. Comparison is done also in a two dimensional simulation to know the differences occurring phenomena and flow inside ejector. Different simulation results obtained between two dimensional and three dimensional simulation. Reverse flow which occurs in the mixing chamber made the static pressure in the area has increased dramatically. Then the variation performed on Exit Nozzle Position (NXP) to determine the changes of the flow of the NCG and the vacuum level of the ejector.Keywords: Ejector, NCG, CFD, Compressible flow.

Optimization of a premixed cylindrical burner for low pollutant emission

A premixed cylindrical burner is numerically and experimentally investigated to realize low pollutant emission. The geometrical parameters of nozzle exit position and nozzle diameter are optimized by using a validated Computational Fluid Dynamics model. The natural gas-air mixing in the mix chamber indicates that the uniformity of methane concentration increases with the increase of distance from ejector outlet. It is found that the nozzle exit position at −3.0mm improves the overall performance of premixed cylindrical burner, when nozzle diameter is not less than 1.6mm. The emission characteristics of nitrogen oxides and carbon monoxide are also examined by experimental approach. It is found that load factor has a great influence on nitrogen oxides and carbon monoxide emissions, but the effect is gradually disappeared when air coefficient is not less than 1.4. When nozzle exit position is −3.0mm, nozzle diameter is not less than 1.6mm and air coefficient is not less than 1.4, the emissions of nitrogen oxides and carbon monoxide are less than 20ppm and 50ppm, respectively.

Optimization of geometric parameters for design a high-performance ejector in the proton exchange membrane fuel cell system using artificial neural network and genetic algorithm

In this study, a CFD model is adopted for investigating the effects of the four important ejector geometry parameters: the primary nozzle exit position (NXP), the mixing tube length (Lm), the diffuser length (Ld), and the diffuser divergence angle (θ) on its performance in the PEM fuel cell system. This model is developed and calibrated by actual experimental data, and is then applied to create 141 different ejector geometries which are tested under different working conditions. It is found that the optimum NXP not only is proportional to the mixing section throat diameter, but also increases as the primary flow pressure rises. The ejector performance is very sensitive to the mixing tube length while the entrainment ratio can vary up to 27% by change in the mixing tube length. The influence of θ and Ld on the entrainment ratio is evident and there is a maximal deviation of the entrainment ratio of 14% when θ and Ld vary from 2° to 8° and 6Dm to 24Dm, respectively. To make sure the correlation of all geometric parameters on the ejector performance, the artificial neural network and genetic algorithm are applied in obtaining the best geometric.

Experimental results with a variable geometry ejector using R600a as working fluid

Experimental results with the first laboratory scale variable geometry ejector (VGE) using isobutane (R600a) are presented. Two geometrical factors, the area ratio and the nozzle exit position, can be actively controlled. The control of the area ratio is achieved by a movable spindle installed in the primary nozzle. The influence of the spindle position (SP) and condenser pressure on ejector performance are studied. The results indicate very good ejector performance for a generator and evaporator temperature of 83 °C and 9 °C, respectively. COP varied between 0.4 and 0.8, depending on operating conditions. The existence of an optimal SP, depending on the back pressure, is identified. A comparison of the benefit of applying the variable geometry design over a fixed geometry configuration is assessed. For example, for a condenser pressure of 3 bar, an 80% increase in the COP was obtained when compared to the performance of a fixed geometry ejector.

Numerical investigation of optimal geometry parameters for ejectors of premixed burner

An ejector of low NOx burner was designed for a gas instantaneous water heater in this work. The flowing and mixing process of the ejector was investigated by computational fluid dynamics (CFD) approach. A comprehensive study was conducted to understand the effects of the geometrical parameters on the static pressure of air and methane, and mole fraction uniformity of methane at the outlet of ejector. The distribution chamber was applied to balance the pressure and improve the mixing process of methane and air in front of the fire hole. A distribution orifice plate with seven distribution orifices was introduced at the outlet of the ejector to improve the flow organization. It is found that the nozzle exit position of 5 mm and nozzle diameter d >1.3 mm should be used to improve the flow organization and realize the well premixed combustion for this designed ejector.