• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.483-494
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• 1998

This study describes the characteristics on impeller discharge flow of a centrifugal compressor with vaneless diffuser. Distorted flow at impeller exit was investigated by measuring of unsteady velocity fluctuation using hot-wire anemometer. As a result, a wake region appears near shroud side and moves to suction side and also to hub side as flow rate decreases. Jet, wake, and their boundary region which can be defined in jet-wake flow model are clearly observed at a high flow rate for the flow coefficient of 0.64, however, as flow rate decreases to the flow coefficient of 0.19, the classification of their regions disappears. Turbulence intensity also increases as flow rate decreases. Measurement error from uncertainty analysis is estimated about 4% at the flow coefficient of 0.19

• Journal of Mechanical Science and Technology
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• v.18 no.11
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• pp.2032-2041
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• 2004

Results from an experimental study of flow distribution in a close-coupled catalytic converter(CCC) are presented. The experiments were carried out with a flow measurement system specially designed for this study under steady and transient flow conditions. A pitot tube was a tool for measuring flow distribution at the exit of the first monolith. The flow distribution of the CCC was also measured by LDV system and flow visualization. Results from numerical analysis are also presented. Experimental results showed that the flow uniformity index decreases as flow Reynolds number increases. In steady flow conditions, the flow through each exhaust pipe made some flow concentrations on a specific region of the CCC inlet. The transient test results showed that the flow through each exhaust pipe in the engine firing order, interacted with each other to ensure that the flow distribution was uniform. The results of numerical analysis were qualitatively accepted with experimental results. They supported and helped explain the flow in the entry region of CCC.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.211-218
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• 2000

Off-design experimental performance was investigated for a small centrifugal compressor, whose impeller diameter is about 125mm, used in an industrial gas turbine. Test rig was designed and manufactured with a radial inflow turbine and a combustor to supply driving power to the compressor. Static pressure was measured on the casing of the impeller, vaneless diffuser, vaned diffuser and volute. Total pressure was obtained using specially fabricated rakes at the vaned diffuser throat and exit. Circumferential nonuniformity was found, near surge, in the Impeller, vaned diffuser and volute region. Spanwise nonuniform flow from the impeller affected the total pressure defects in the vaned diffuser region. Static pressure distortion in the circumferential direction in the volute was found near surge, where the minimum occurred near 140 degree position.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.751-756
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• 2001

An experimental model of the advanced mixing control in the parallel supersonic-subsonic mixing jet (M$_1$=1.78 and M$_2$=0.30) is numerically simulated. An oscillating wall boundary condition is used as the modeling of a wall cavity for mixing enhancement. The obtained pitot pressure distributions along cross sections at the developing region of the turbulent jets are validated from the good agreement with equivalent experimental data. The similarity solution of dimensional analysis also coincides with this numerical result at the self-similar region sufficiently far from the jet exit.

• Journal of the Korean Society for Precision Engineering
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• v.5 no.4
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• pp.24-31
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• 1988

The Upper Bound Solution has been used to investigate the effect of the various parameters on the floating-plug tube-drawing precess. A kinematically admissible velocity field considering the change of the tube thickness is proposed for the deformation process. Taking into account the position of the plug in the deforming region, shear energy at entrance and exit, friction energy on contact area, homogeneous energy are calculated. The theoretical values in proposed velocity field are good agreement with experimental values, It is investigated that the tube thickness in the deforming region is changed slightly toward minimization of deforming energy and then the drawing stress in lower than the crawing stress in the velocity field that the tube thickness is uniform.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.593-596
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• 2008

Because of good performance of heat transfer characteristics, impinging jets are widely used in many industries for cooling or heating. And the present num erical studies attempt to show the effects of impinging jet. This paper considers the application of the turbulent models to impinging jet flow with pulsed inlet. It is assumed two-dimensional turbulent flows. The jet Reynolds num ber is set at 23,000 and the distance from the exit of the nozzle to the plate is 3 times larger than the diam eter of the nozzle. The influence of the Strouhal num ber(pulsation frequency) on Nusselt number at the impinging region is investigated. Strouhal numbers are ranged 0.0 to 0.5 and the forcing amplitudes are 1%,5%,9% of mean inlet velocity. In this study, the Nusselt number at the impinging region is sensitive to the pulsation frequency. Heat transfer coefficient strongly increase at Strouhal num ber of 0.4.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.221-221
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• 2000

The heat exchange part in a modern multi-type air-conditioning system employs multiple-pass heat exchangers. The heat-transfer performance of an each pass in such an exchanger depends strongly on the length of the two-phase region and the mass flow of the refrigerant. The total length and diameters of the pipes, the exit conditions, and the arrangement of each pass as well as the geometrical shape of the distributor at the branching sections are considered to be major factors affecting the heat-transfer performance. The refrigerant commonly used in these systems is HCFC-22. The two objectives of this paper are to investigate the characteristics of the refrigerant flow rate and the superheat in the evaporator of a multi-type air-conditioning system for a single or simultaneous operating conditions and to control the superheat and the refrigerant flow rate of the evaporator.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.5
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• pp.470-478
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• 1991

In this study, a variety of characteristics were shown experimentally under mechanically unbalnced states expected in a practicl system that linear motor is used as a driving motor of magneticlly levitated transit and the design criterion of the linear motor has been proposed. Since, with slip being at 0.1, end effect was reduced a little to increase thrust about 6.14 percents in case thatsinusoidal current conducted 5[A] in short coil at each end of linear motor for compensation of it, if the ratio of sinusoidl current versus input currents is adjusted properly, it is thought that this method small be effective one. And if the gap of exit region is bigger than that of entry region, end effect will be reduced. As a result, more effective driving will be obtained.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.3
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• pp.183-190
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• 1992

The Collins cryocooler is numerically analysed with the optimization technique, and the optimum operating and design conditions are searched. This paper shows that liquefied helium quantity has an external maximum w.r.t. the total mass flow rate, the mass flow rates through expander and the capacities of heat exchangers. The liquefied helium quantity increases as the compressor exit pressure of the cryocooler does. The maximum quantity of liquefied helium and the maximum coefficient of performance have been found to exist in extremum, depending on the ratios of each heat exchanger capicities to the total one. At the optimum condition, the capacity of heat exchanger in high temperature region is larger than that in low temperature region.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.302-312
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• 1992

Three dimensional velocity measurements of a 35.deg. inclined jet issuing into turbulent boundary layer on both concave and convex surfaces have been conducted. To investigate solely the effect of each curvature on the flow field, streamwise pressure variations are minimized by adjusting the shape of the opposite wall in the curved region. From the measured velocity components, streamwise mean vorticities are calculated to determine jet-crossflow interface. The results on convex surface show that the injected jet is separated from the wall and the bound vortex maintains its structure far downstream. On concave surface, the secondary flow in the jet cross-sections are enhanced and in some downstream region from the jet exit, the flow on the concave surface has been developed to Taylor-Gortler vortices