• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.554-560
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• 2005

A new method to improve the efficiency of a hydrogen fuel cell system was introduced by using variable sonic/supersonic ejectors. To obtain the variable area ratio of the nozzle throat to ejector throat which controls the mass flow rate of the suction flow, the ejectors used a movable cylinder inserted into a conventional ejector-diffuser system. Experiments were carried out to understand the flow characteristics inside the variable ejector system. The secondary mass flow rates of subsonic and supersonic ejectors were examined by varying the operating pressure ratio and area ratio. The results showed that the variable sonic/supersonic ejectors could control the recirculation ratio by changing the throat area ratio, and also showed that the recirculation ratio increased fur the variable sonic ejector and decreased for the variable supersonic ejector, as the throat area ratio increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.640-647
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• 2002

An experimental investigation or the sonic and supersonic air ejector systems has beer conducted to develop design and prediction programs for practical ejector system. Five different primary nozzles have been employed to operate the ejector systems in the ranges of low and moderate operating pressure ratios. The ejector operating pressure ratio for the secondary chamber pressure to be minimized has a strong influence of the ejector throat ratio. The pressure inside the ejector diffuser is not dependent on the primary nozzle configurations employed but only a function of the ejector operating pressure ratio. Experimental results show that a supersonic ejector system is more desirable for obtaining high vacuum pressure of the secondary chamber than a sonic ejector system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.8
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• pp.1128-1138
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• 2000

Pumping action in ejector systems is generally achieved through the mixing of a high-velocity and high-energy stream with a lower-velocity and lower-energy stream within a duct. The design and performance evaluation of the ejector systems has developed as a combination of scale-model experiments, empiricism and theoretical analyses applicable only to very simplified configurations, because of the generic complexity of the flow phenomena. In order to predict the detailed performance characteristics of such systems, the flow phenomena throughout the operating regimes of the ejector system should be fully understood. This paper presents the computational results for the two-dimensional supersonic ejector system with a second throat. The numerical simulations are based on a fully implicit finite volume scheme of the compressible Reynolds-averaged Navier-Stokes equation in a domain that extends from the stagnation chamber to the diffuser exit. For a wide range of the operating pressure ratio the flow field inside the ejector system is investigated in detail. The results show that the supersonic ejector systems have an optimal throat area for the operating pressure ratio to be minimized.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.479-484
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• 2000

For the purpose of a cost effective design of practical subsonic/supersonic ejector systems, an experiment was carried out using a superheated steam as a primary driving flow. The superheated steam jet was produced by several different kinds of subsonic and supersonic nozzles. The secondary flow of atmospheric air inside a plenum chamber was drawn into the primary steam jet. The vacuum performance of the plenum chamber was investigated for a wide range of the ejector operation pressure ratio. The result showed that the static pressure of the mixed flow at the ejector throat is only a function of the ejector operation pressure ratio, regardless of the primary nezzle type employed.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.520-524
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• 2000

A ejector system is one of the fluid machinery, which has been mainly used as an exhaust pump or a vacuum pump. The ejector system has often been pointed out to have only a limited efficiency because it is driven by pure shear action and the mixing action between primary and secondary streams. In the present work, numerical simulations were conducted to investigate the effects of the geometry and the mass flow ratio of supersonic ejector-diffuser systems on their mixing performance. A fully implicit finite volume scheme was applied to solve the axisymmetric Navier-Stokes equations, and the standard ${\kappa}-{\varepsilon}$ turbulence model was used to close the governing equations. The flow fields of the supersonic ejector-diffuser systems were investigated by changing the ejector throat area ratio and the mass flow ratio. The existence of the second throat strongly affected the shock wave structure inside the mixing tube as well as the spreading of the under-expanded jet discharging from the primary nozzle, and served to enhance the mixing performance.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.646-651
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• 2001

The present study is an experimental work of the sonic/supersonic air ejector-diffuser system. The pressure-time dependence in the secondary chamber of this ejector system is measured to investigate the steady operation of the ejector system. Six different primary nozzles of two sonic nozzles, two supersonic nozzles, petal nozzle, and lobed nozzle are employed to drive the ejector system at the conditions of different operating pressure ratios. Static pressures on the ejector-diffuser walls are to analyze the complicated flows occurring inside the system. The volume of the secondary chamber is changed to investigate the effect on the steady operation. the results obtained show that the volume of the secondary chamber does not affect the steady operation of the ejector-diffuser system but the time-dependent pressure in the secondary chamber is a strong function of the volume of the secondary chamber.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.8 s.239
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• pp.934-939
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• 2005

Starting pressure of a supersonic ejector with a second-throat was investigated. In case of mixing chamber length longer than a critical length, starting pressure is in proportion to length of the mixing chamber. In this study, we assumed that the ejector starts when the primary supersonic flow reaches inlet of the second-throat and the distance of the supersonic flow traveling can be expressed by multiplying an empirical factor to the first diamond shock length of overexpanded flow. To calculate the overexpanded supersonic flow, a mixing model was employed to compute secondary flow pressure and the result was applied to back pressure condition of overexpanded flow calculation. In the result, for three cases of primary nozzle area ratio, we could get accurate model of predicting the starting pressure by selecting a suitable empirical factors around 3.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.329-334
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• 2001

In order to investigate the operating characteristics of a supersonic steam ejector, the axisymmetric, compressible, Reynolds-averaged, Navier-Stokes computations are performed using a finite volume method. The secondary and back pressures of the ejector system with a second throat are changed to investigate their effects on the suction mass flow. Three operation modes of the steam ejector system, the critical mode, subcritical mode and back flow mode, are discussed to predict the critical suction mass flow. The present computations are validated with some experimental results. The secondary and back pressures of the supersonic steam ejector significantly affect the critical suction mass flow. The present computations predict the experimented critical mass flow with fairly good accuracy. A good correlation is obtained for the critical suction mass flow. The present results show that provided the primary nozzle configuration and secondary pressure are known, we can predict the critical mass flow with good accuracy.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.469-473
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• 2009

The supersonic gas ejector, as gas dynamic appliance, has been applied for a long time because of simplicity and reliability. However, for the prediction of ejector performances with given parameters, that is, working gas pressure and the nozzle shape, it is necessary to raise accuracy of modelling for properties of ejector gas flow. The purpose of the represented work is to compare one-dimensional modelling and numerical results with experimental results. The ejector with a conic nozzle has been designed and tested (Mach number at the nozzle exit section was 3.31, the nozzle throat diameter - 6 mm). Working gas - nitrogen, was brought from system of gas bottles. Diameter of the mixture chamber at the nozzle exit section was limited by condensation temperature of nitrogen and equaled 20 mm. The one-dimensional theory predicted the minimal starting pressure equaled 8.18 bar (absolute) and 0.051 bar in the vacuum chamber. Accordingly the minimal starting pressure was 9.055 bar and 0.057 in the vacuum chamber bar have been fixed in experiment.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.2
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• pp.70-77
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• 2005

An axisymmetric supersonic ejector equipped with a converging-diverging diffuser was built and pressure at various locations along the ejector-diffuser system was recorded with emphasis on the supersonic starting of the secondary flow. In order to find the effects of the opening size of the secondary flow, a number of openings were used with a constant primary pressure. Supersonic starting was possible only for d/D, the ratio of the opening diameter and the diffuser throat diameter, less than 0.306. for larger values of d/D, the ejection begins at subsonic secondary flow condition. With the closure of the opening, the primary flow brings the normal shock downstream of the converging-diverging diffuser And the starting of the ejector continues even after the closure was removed.