• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.318-322
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• 2009

Supersonic ejectors are simple mechanical components, which generally perform mixing and/or recompression of two fluid streams. Ejectors have found many applications in engineering. In aerospace engineering, they are used for altitude testing of a propulsion system by reducing the pressure of a test chamber. It is composed of three major sections: a vacuum test chamber, a propulsive nozzle, and a supersonic exhaust diffuser. This paper aims at the improvement of ejector-diffuser performance by focusing attention on reducing exhaust back flow into the test chamber, since alteration of the backflow or recirculation pattern appears as one of the potential means of significantly improving low supersonic ejector-diffuser performance. The simplest backflow-reduction device was an orifice plate at the duct inlet, which would pass the jet and entrained fluid but impede the movement of fluid upstream along the wall. Results clearly showed that the performance of ejector-diffuser system was improved for certain a range of system pressure ratios, where as there was no appreciable transition in the performance for lower pressure ratios and the orifice plate was detrimental to the ejector performance for higher pressure ratios. It is found that an appropriately sized orifice system should produce considerable improvement in the ejector-diffuser performance in the intended range of pressure ratios.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.890-894
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• 2015

Recently, research on high-efficiency refrigeration cycles that apply an ejector to basic cycles has progressed actively. The role of the ejector and the performance of refrigeration cycles are subordinate to ejector locations. In this study, the performance of three refrigeration cycles with different ejector locations is compared and analyzed. The results showed an increased COP in all cycles due to the application of the ejector, with the highest increase of 44% compared to a basic refrigeration cycle. The ejector refrigeration cycle proposed in this study presents the highest COP, 3.47. Moreover, the decrease in condensation capacity in Bergander's cycle, Xing's cycle, and our proposed ejector refrigeration cycle went up to 21%. In refrigeration cycles applying the ejector, the pressure ratio of the ejector, the vapor fraction of discharge, and compression ratio are important factors for COP enhancement. For this reason, detailed and accurate control of these is significant.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.321-325
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• 2010

Supersonic ejectors are simple mechanical components, which generally perform mixing and/or recompression of two fluid streams. Ejectors have found many applications in engineering. In aerospace engineering, they are used for altitude testing of a propulsion system by reducing the pressure of a test chamber. It is composed of three major sections: a vacuum test chamber, a propulsive nozzle, and a supersonic exhaust diffuser. This paper aims at the improvement of ejector-diffuser performance by focusing attention on reducing exhaust back flow into the test chamber, since alteration of the backflow or recirculation pattern appears as one of the potential means of significantly improving low supersonic ejector-diffuser performance. The simplest backflow-reduction device was an orifice plate at the duct inlet, which would pass the jet and entrained fluid but impede the movement of fluid upstream along the wall. Results clearly showed that the performance of ejector-diffuser system was improved for certain a range of system pressure ratios, whereas the orifice plate was detrimental to the ejector performance for higher pressure ratios. It is also found that there is no change in the performance of diffuser with orifice at its inlet, in terms of its pressure recovery. Hence an appropriately sized orifice system should produce considerable improvement in the ejector-diffuser performance in the intended range of pressure ratios.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.12
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• pp.1673-1680
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• 2003

It is essential to operate chemical lasers with supersonic ejector system as the laser output power goes up. In this research, ejector design parameter study was carried out for optimal ejector design through understanding the ejector characteristics and design requirements for chemical lasers operating. Designed ejector was 3D annular type with 2$^{nd}$ -throat geometry and pressurized air was used for primary flow. Ejector design was carried out with two steps, quasi-1D gas dynamics was used for first design and commercial code was used to verify the first design. In this study, to get the effect of ejector geometry on its performance, three cases of primary nozzle area ratio and 2$^{nd}$ -throat cross sectional area and two cases of 2$^{nd}$ -throat L/D ratio experiments were carried out. Primary and secondary pressures were measured to get the mass flow rate ratio, minimum secondary pressure, ejector starting pressure and unstarting pressure at every case. In the result, better performance than design level was shown and optimal ejector design method for chemical lasers was obtained.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.7
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• pp.362-368
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• 2015

This paper presents a numerical study on the performance of a vapor compression cycle equipped with an ejector as an expansion device to improve the COP by reducing the expansion loss and compressor work. The simulation is carried out using a model based on the conservation of mass, energy and momentum in the ejector. From the results of the simulation, the vapor compression cycle equipped with an ejector showed a maximum COP improvement of 14.0% when using R134a refrigerant and 16.8% when using R1234yf. In addition, the performance of the system with an ejector represents the increased performance as the temperature difference between condensing and evaporating increased.

• Journal of the Korean Solar Energy Society
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• v.34 no.4
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• pp.45-50
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• 2014

In this paper, the Ocean Thermal Energy Conversion(OTEC) with vapor-vapor ejector is proposed newly. At this OTEC system, a vapor-vapor ejector is installed at inlet of condenser. The vapor-vapor ejector plays a very important role in increasing of the production work of low-stage turbine throughout the decrement of outlet pressure of ejector. The performance analysis is conducted for optimizing the system with HYSYS program. The procedure of performance analysis consists of outlet pressure of high turbine, the mass ratio of working fluid at separator, total working fluid rate, and nozzle diameters of vapor-vapor ejector. The main results is summarized as follows. The nozzle diameter is most important thing in this study. When each nozzle diameter of vapor-vapor ejector is 10 mm, the efficiency of OTEC system with vapor-vapor ejector shows the highest value. So it is necessary to set the optimized nozzle diameters of vapor-vapor ejector for achieving the high efficiency OTEC power system.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.52-60
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• 2019

In this study, the performance and structure of a parallel ejector comprised of multiple single ejectors were confirmed through numerical analysis. The same design variables (mass suction ratio, compression ratio, and expansion ratio) relevant to the performance of a single ejector were considered in the design of the parallel ejector. Analytical results showed that there was no significant difference in the performance of either system related to the operating mass suction ratio; however, the systemsize was significantly reduced. In addition, it was confirmed that when ejectors of the same performance capacity are arranged in parallel, the combined mass suction ratio is lower than that of the single ejector, allowing a lower pressure to be realized. The results of the analysis indicated that the parallel ejector's performance is not significantly different from that of any single ejector, but confirmed that the parallel ejector can offer a configurationdependent advantage in size and operation.

• Journal of Advanced Marine Engineering and Technology
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• v.15 no.5
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• pp.30-37
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• 1991

Steam ejector systems are widely used for the evacuation systems because of their high working confidence and simlicity. And recently these are used as the thermo-compressors in various energy saving systems. In this practical experiment, we have obtained the results as follows : (1) The velocity coefficient of the motive steam nozzle was 0.92-0.98. (2) The optimal area ratio was 0.00625 at pressure ratio 5.2 and expansion ratio 101.3. (3) The performance and efficiency of the steam ejector were mainly affected by the axial position of nozzle. (4) The good performance of the domestic manufactured steam ejector was confirmed in comparison with the foreign one. And by experimental results, we have carried out the improvement of Computer Aided Design Program of steam ejector which will be helpful for systematic research into the steam ejector.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.8
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• pp.946-952
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• 2005

The $CO_{2}$ refrigeration cycle is expected to reduce the compressor work and increase the COP by applying two-phase ejector as a device for the recovery of dissipated expansion energy. In this study, the performance of the cycle was simulated and effects of the ejector shapes on the performance of the $CO_{2}$ refrigeration cycle were investigated. The following results were obtained through the cycle simulation. The COP of the $CO_{2}$ refrigeration cycle with two-phase ejector flow which expansion is occured in the isentropic manner is increased by a maximum of 24 $\%$ than the basic cycle with expansion valve If the velocity nonequilibrium in the mixing process is assumed the COP of the cycle is increased with the increase of the length and the decrease of the section area of the mixing tube. The best cycle performance is obtained when the divergent angle of diffuser is 7.

• International Journal of Air-Conditioning and Refrigeration
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• v.17 no.3
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• pp.100-106
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• 2009

As an effort to prevent environmental problems caused by ozone depletion and global warming, alternative refrigerants are being developed, and one of the candidates is carbon dioxide. To overcome slightly low efficiency of $CO_2$ refrigeration system, air-conditioning cycle using an ejector was suggested. Ejector compensates throttling loss in an expansion device by reducing compression work. In this study, the ejector refrigeration cycle using $CO_2$ as a refrigerant is investigated to understand the effect of the mixing section diameter and refrigerant charge amount on the performance. If mixing section diameter is too large or too small, either cases show low performance. The optimum refrigerant charge amount which gives the best performance is found for standard operating conditions. The air-conditioning cycle was analyzed for several operating conditions.