جستجوی مقالات مرتبط با کلیدواژه « اجکتور » در نشریات گروه « فنی و مهندسی »

This paper introduces a novel approach to enhance the performance of a two-phase steam and air ejector through primary supersonic nozzle designs with uncircular cross-sections. Experimental tests evaluated the impact of these novel nozzle designs ،which included a star shape ،a simple square ،a square skewed in the direction of the nozzle axis ،a special sketch ،and a simple circular cross-section as the reference nozzle ،on the ejector's performance. The results indicated that the novel nozzles demonstrated the capability to enhance the ejector's entrainment ratio by up to 12% compared to the conventional circular cross-section reference nozzle. To validate and gain further insights into the novel nozzle designs ،computational fluid dynamics (CFD) simulations were also conducted. The integration of CFD simulations and experimental data showcased the potential of these uncircular cross-section nozzles to improve the ejector's performance. The findings offer promising opportunities for optimizing ejector configurations ، paving the way for more efficient and innovative solutions in various engineering applications.

This paper investigates the effect of a Helmholtz resonator with one or two pairs of deep cavities on the mixing chamber of a subsonic ejector to determine its impact on the ejector's entrainment ratio. The study utilizes numerical analysis, where the depth, location, and number of cavities were varied while keeping the width of the resonator constant. The Fluent software solved the Unsteady Reynolds-Averaged Navier-Stokes equations with the k- εturbulence model. The presence of the cavity at the beginning, middle, and end of the mixing chamber reduced the entrainment ratio by 0.6%, 3.8%, and 6.6%, respectively, and the presence of the second cavity at the positions of 20, 40, and 60 mm with respect to the first cavity reduced the entrainment ratio by 9.9%, 10.1%, and 10.2% respectively. The depth effect was studied at a distance of 20 mm for a pair of cavities at depths of 75, 100, and 125 mm causing a reduction of 4.9%, 9.9%, and 13.1% in entrainment ratio. The study also observed longitudinal and pulsating oscillations inside the mixing chamber due to the simultaneous filling and emptying of opposite cavities. Furthermore, the amplitudes of the pressure oscillations in the first pair were weaker than those in the second pair. In the final part of the research, the effect of primary flow fluctuation was also investigated, the results of which showed that the primary flow fluctuation increases the entrainment ratio by 5.2% due to the increase of effective mixing between the primary and secondary flow.

The present study aimed to introduce two novel power-refrigeration combined cycles into optimal usage of LNG cryogenic energy and reducing exergy losses due to high-temperature difference in the heat transfer process. The combined cycles include a compression-ejector refrigeration cycle and two low and high-pressure Rankine cycles in which the power required to operate the compression-ejector refrigeration cycle’s compressor is provided by the power generated by the two-cycle Rankin turbines. Increasing the cooling energy compared to direct LNG evaporation is considered as the benefits of the novel combined cycles. A thermodynamic analysis, along with optimizing both novel combined power-refrigeration cycles, was performed through the first and second thermodynamics laws and the fixed surface model assumption for the ejector. Analyzing the design parameters demonstrated that the maximum thermal and exergy efficiency and maximum refrigeration increasing ratio in both novel combined power-refrigeration cycles increase as the pump discharge pressure increases and the output pressure of Rankine cycle turbine reduces. The maximum thermal and exergy efficiency in cycle (І) were 77.31% and 23.69%, and 87.49% and 23.95% in cycle (ІІ), respectively through performing optimization in the boundaries set for the design parameters. Finally, the highest refrigeration increasing ratio to direct evaporation of LNG for cycle І and ІІ was 63.37% and 73.9%, respectively.

Geometry of primary nozzle is one of the parameters that affect the performance of a supersonic ejector. In this paper, the effect of using parallel-flow primary nozzle on the performance of a supersonic ejector is experimentally investigated. For this purpose, two primary nozzles, conical and parallel-flow, with the same converging portion and the same ratio of exit surface to throat surface, have been used. The parallel-flow nozzle diverging curve is calculated using the characteristic method. At various positions of the primary nozzle, characteristic curves of the ejectors with conical and parallel-flow nozzles have been compared.The results show that by changing the primary nozzle diverging curve from conical to parallel-flow, at the same position of primary nozzle, the entrainment ratio increases in both critical and subcritical regions. In the critical region, entrainment ratios obtained by the primary nozzle positions 5 mm, 10 mm, and 15 mm are increased by 9.5%, 4.5% and 4.7%, respectively.The optimum position of the primary nozzle changes with changing the primary nozzle diverging curve. At the suitable position of the primary nozzles and without any reduction in critical pressure, the maximum relative increase of entrainment ratio in the critical region is 8%.

In the present research, a novel bi-evaporator combined cooling and power cycle based on the integration of a double-stage organic Rankine cycle and an ejector refrigeration cycle is devised to recycle heat from the exhaust gas of a marine diesel engine. Instead of using conventional pure organic fluids, various appropriate zeotropic mixtures are screened for the proposed system and the results are discussed in terms of the first and second laws of thermodynamics. The results indicated that by recycling 434kW energy from the exhaust gases and using R142/Pentane with 51/49 percent a maximum thermal efficiency of 43.28% and an overall cooling load of 166.36 kW can be achieved. In this case, the net produced electricity and exergy efficiency are obtained as 21.83 kW and 20.22% which can be increased by selecting other appropriate mixtures. Additionally, using R142/Pentane with 51/49 percent as the working mixture, it is figured out that the auxiliary vapor generator contributes to the highest exergy destruction by 62.3 kW out of overall exergy destruction of 122.15 kW. Also, the energy and exergy efficiencies of the system can be increased simultaneously by increasing the evaporator bubble point temperature.

The ejector is the most important part of the ejection refrigeration cycle. Due to the complexity and different phenomena, such as suction, mixing, and shock that occur inside the ejector, it requires separate and accurate analysis. This study, for the first time, numerically was investigated the effects of secondary inlet pressure on the ejector flow. The effects of this parameter on pressure, Mach number and temperature inside the ejector were studied. The governing equations were solved by the finite volume method and compressible, two-dimensional, axisymmetric and fully turbulent flow. By comparing numerical results with experimental and analytical results, there is a reasonable agreement between them. In order to obtain the best performance of an ejector, at different secondary inlet pressure, the entrainment ratio and exergy efficiency were computed and compared to reach the best condition. The results show that there is inverse flow at low pressure less than 0.8 bar, but it becomes better by increasing the pressure up to 1.5 bar and more than that, no improvement was found. By reducing the secondary inlet pressure from the optimal pressure of 1.5 bar until the reversal flow occurs, the entrainment ratio decreases by about 105% and the exergy efficiency by about 64%.

In this paper, the performance of four prevalent combined ejector-vapor compression cycles are compared. A non-iterative algorithm for the analysis of ejector performance in critical operational mode has been used. Moreover, using flow parameters is proposed for estimating loss coefficient in the mixing process rather than using geometrical specification and operating conditions of the ejector. The effects of the operating conditions and refrigerant type on the coefficient of performance, thermal coefficient of performance, and ejector entrainment are investigated and analyzed. Results show that, at high condenser temperatures, the difference between coefficient of performance of combined cycle and conventional vapor compression cycle significantly decreases. Combined cycles which only utilize the waste heat of the condenser in the vapor compression sub-cycle have a lower coefficient of performance than those cycles using an external heat source and can be used in smaller rang of condenser and generator temperatures.

Ejector is used as a key component in ejector refrigeration cycle. A supersonic ejector with optimal performance reduces energy consumption in refrigeration system and improves its performance. In this paper, the effect of using parallel flow primary nozzle on the performance of a supersonic ejector used in an ejector refrigeration cycle, with steam as working fluid, is numerically investigated. For this purpose, two primary nozzles, conical and parallel flow, with the same converging portion and the same ratio of exit surface to throat surface, have been used. The parallel-flow nozzle diverging curve is calculated using the characteristic method. Numerical simulations have been performed using the Ansys-Fluent software. The results show that by changing the primary nozzle diverging curve from conical nozzle to parallel flow nozzle, variation of entrainment ratio in the critical region will be negligible, but in the subcritical region, it is significant. The maximum relative variation of entrainment ratio in subcritical region of the parallel flow nozzle is +17.3%. Also, by changing the diverging curve of the primary nozzle, critical pressure increases by 1 mbar and the physics of the ejector internal flow changes.

Ejectors are as widely used as in food industries to refrigeration cycles and power plants. Since condensers of steam power plants are operated in vacuum conditions, there is a continuous air leakage, which results in metal corrosion and reduction in efficiency. Therefore, ejectors are used in these systems to remove the air. Over time, leakage increases, which requires more efficiency of ejector. Entrainment ratio (ER) is defined as the main criterion for ejector efficiency and leads to better performance if increased and also depends considerably on geometry of ejector. The aim of this research is to increase efficiency of ejector of Touss Power Plant by simultaneously changing nozzle exit position (NXP) and converging angle of mixing chamber. The main geometry of ejector was simulated by FLUENT and primary results were validated with experimental and computational data. Then, different geometries with simultaneous change in NXP and converging angle of mixing chamber were selected in the first step of Taguchi method and simulated by FLUENT. Geometries of the second step of Taguchi method were selected and designed based on the results of signal-to-noise ratio for the above-mentioned parameters and the values of entrainment ratio in the first step. An identical approach was followed for the third step. Final results showed 34% increase in entrainment ratio and also revealed that there is an optimum value for NXP and converging angle of the mixing chamber around which the value of entrainment ratio is maximum.

In this paper, parametric analysis and optimization of the transcritical ejector refrigeration cycle using different working fluids have been proposed which can be employed in the parts of solar energy processes. The main advantages of using ejector in the refrigeration cycles, which often use instead of the compressor, are simplicity in construction and maintenance, high reliability and low cost. In this study, the transcritical ejector refrigeration cycle is modelled using EES software and the effects of different parameters such as temperature and pressure of different parts of cycle on the coefficient of performance and entrainment ratio are investigated. In continued, the coefficient of performance of the transcritical ejector refrigeration cycle for four different working fluids is optimized using the combination the Artificial Neural Network and Particle Swarm Optimization algorithm.

In this research study, a novel ORC cycle is proposed to improve the efficiency and power generation of the basic ORC cycle. In this proposed new cycle, an ejector, a second stage evaporator and a regenerator are integrated in the basic ORC cycle. Steam from the second stage evaporator enters to the ejector as the primary fluid, after decrease in mixture pressure, it tends to increase the suction of the secondary fluid from the turbine outlet (steam from the turbine). Also steam enters to the regenerator, before the ejector, and by this way supplies a part of required energy for the first stage evaporator and increases the efficiency as well. For thermodynamic modeling a code was developed in the Engineering Equation Solver (EES) software. In addition, different working fluids (R600, R245fa, R236fa, Cis-2-Butene) were examined to evaluate the thermodynamic performance of the basic ORC cycle and new proposed cycle. The results show efficiency increase of the new cycle compared with that of the basic ORC cycle, the value of which depends on the working fluid, as the maximum efficiency increase of 17.5% is noticed.

In this paper, a new 1-dimensional model is developed to predict the ejector performance. This model is based on the gas dynamics with the principles of mass, momentum and energy conservation. The model is able to calculate the ejector entrainment and area ratios for different thermodynamic conditions with high accuracy. Due to the frictional losses in different parts of the ejector, isentropic efficiencies are considered for the ejector. The results of the validation show that the maximum relative difference, compared with the experimental data, in calculating the area and entrainment ratios are 13.27% and 5.8% respectively, when in the one dimensional model reported in the literature these values are 22.04 % and 9.78 % respectively. The results also indicate that with decreasing the ejector back pressure or increasing the evaporator pressure, area and entrainment ratios of the ejector increase.

Steam jet ejectors are the essential part in refrigeration and air conditioning, desalination, petroleum refining, petrochemical and chemical industries. A greater understanding of flow physic inside an ejector plays an important role in its performance improvement. In this study, analytical algorithm is developed for design of steam ejectors. The algorithm gives the flow ratio (motive to suction flow rate) as a function of the expansion ratio and the pressures of the entrained vapor, motive steam and compressed vapor. The compression ratio and back pressure variations were studied in ejector flow ratio with expansion ratio of 5 and 50. It showed that compression ratio increase by increasing the flow ratio. Also in a similar flow rate, compression ratio for ejector with expansion ratio of 50 is greater than compression ratio in the ejector with expansion ratio of 50, due to more vacuum in the case with expansion ratio 50. Then, the code results were compared with experimental results that showed appreciate agreement with other results.Finally, Mach number variations from nozzle exit to discharge diffuser were obtained by code. Results showed that the pressurized condition causes the lowering of expansion angle, thus resulting in smaller jet core and larger effective area. The expanded wave is further accelerated at a lower Mach number. Therefore, the momentum of the jet core is reduced. However, the enlarged effective area allows a larger amount of secondary fluid to be entrained.

An ejector is a pumping device that uses a high-speed primary fluid jet to entrain a secondary stream. In this work, using CFD we simulate subsonic air – air ejector numerically. Governing equations including continuity, momentum and energy equations are solved numerically based on finite volume method. Numerical simulation is carried out in 3 dimensions and flow is assumed to be conservative, viscous and turbulent. To simulate turbulences, Reynolds averaged Navier–Stokes, K-ε Standard, K-ε RNG, K-ε Realizable, K-ω Standard and K-ω SST are applied. Ejecting coefficient for various pressure ratios was an effective parameter which was used to validate numerical results. Error was at its minimum for K-ε RNG turbulence model. Therefore, it was used to simulate turbulences. After validating results, we analyzed the effect of geometrical parameter of diffuser outlet diameter and divergence angle on performance of subsonic air – air ejector. Results demonstrate that in addition to divergence angle, diffuser outlet diameter has a significant influence on performance and efficiency of such devices.

This paper identifies the inefficiencies of a proposed energy conversion system to improve its performance. The conventional exergy analysis is unable to identify these inefficiencies because it does not consider the interactions among the system components. The advanced exergy analysis does this however. The main role of advanced exergy analysis is to provide engineers with additional useful information for improving the design and operation of energy conversion systems. The information is achieved by splitting the exergy destruction into endogenous/exogenous and unavoidable/avoidable parts. In the present paper both the conventional and advanced exergy analyses are employed. The splitting raises the accuracy of exergy analysis and facilitates the system improvement. The used method in this paper for splitting is thermodynamic cyclemethod which considers hybrid cycles in each of which only one of the component operates on the real condition and the rest operate under ideal condition. Advanced exergy analysis of ejector-expansion trans-critical CO2 cascade refrigeration system consisting of two refrigeration systems, is discussed. The results indicate that although the conventional exergy analysis shows the highest exergy destruction for the ejector, the advanced exergy analysis suggests improving the gas cooler performance first. The compressor, ejector and evaporator are in the next stages for improvement because of their maximum value of endogenous avoidable exergy destructions.

In this paper, the efficiency of Proton membrane exchange (PEM) fuel cell system by using ejector for returning the additional fuel in the fuel supply circuit and comparison with conventional systems, with compressor in fuel supply circuit, are studied. For this purpose a semi - analytical developed model for calculating the amount of efficiency increment, as well as the amount of power saving as a result of employing ejector in the fuel cell return line is provided by extending the previous models. In this developed model the important stack design parameters and ejector design parameters are correlated by presenting a new dimensionless parameter. The results for a typical fuel cell show that the amount of efficiency increment at different values of current density is different and there is a maximum point for it. The amount of power saving as a result of employing ejector compared with fuel cell power is considerable and will increase with increasing the current density. These results indicate that the ejector for those applications that require high power (for instance the transport applications) is more efficient.

In this article, an algorithm for designing of a supersonic wind tunnel injection nozzle ejector is presented and based on this algorithm, a new ejector is designed for a supersonic wind tunnel. The injection nozzle consists of a volute, a nozzle, and several vanes. Designed injection nozzle is simulated numerically, and the results are compared with thepresent injection nozzle. The results show the efficiency in the designed version is higher about 2.1%. Besides, the flow uniformity of the new injection nozzle is better and other are occurred in it. Scale-up and mapping the pre designed aerodynamic curves with inverse design method, and use it for other similar cases is one of the innovations of this article.

In this article، a combined GAX-ejector absorption refrigeration cycle is proposed and its performance is compared with those of combined single effect-ejector، simple GAX and single effect absorption refrigeration cycles. For the ejector، based on the Keenan''s theory، a new model is developed and validated and then is combined with the developed models in the EES software (for simulating the processes in the cycles). After obtaining the optimum critical area ratio for the ejector، three different ejectors، with the mentioned specification، are selected for the combined GAX-ejector and combined single effect-ejector cycles. The performance of these cycles is investigated through changing their evaporator and generator temperatures. Results indicate that، at identical conditions، the COP and second law efficiency of the combined GAX-ejector cycle are around 25% and 16% higher than those of the combined single effect-ejector absorption refrigeration cycle. In addition، it is observed that as the generator temperature increases from 140 oC to170oC، the COP and second law efficiency of combined GAX-ejector cycle are maximized at a particular generator temperature. However، at similar condition، an increase in generator temperature results in a decrease of the COP and second law efficiency of combined single effect-ejector refrigeration cycle.

In this study، convergent nozzle ejector in the PEM fuel cell system is analyzed. This method can reduce the parasitic power of the fuel cell، recycle the unconsumed hydrogen to the fuel cell to increase the fuel usage efficiency، utilize the pressure potential energy of hydrogen and regulate the anode humidity with the recycle gas. For this purpose، continuity، momentum، energy and state equations are solved by numerical methods and effects of pressure drop (through the channel towards the anode)، operating pressure and temperature of the fuel cell and also nozzle diameter on the ejector performance was analyzed. With decreasing of pressure drop، even in primary lower pressure، increasing of performance pressure the performance of ejector will improved. The temperature increase has no effect on the performance of the ejector itself، but has enormous effect on the fuel cell. Increasing the diameter ratio of the constant diameter zone to the nozzle diameter leads to increasing of recirculation anode line of the fuel in higher pressure.