• Solar Energy
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• v.15 no.3
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• pp.127-140
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• 1995

This experimental study was carried out to examine the heat transfer characteristics of a 2-dimensional impinging air jet on a flat plate with a set of square rods. The objectives of the study were to investigate the flow and heat transfer characteristics caused by the square rods. Experiment was carried out first without using the rods to establish the baseline heat transfer performance. Then, rods of different widths and clearances were installed to cause the turbulence on the fluid flow. When rods are installed in front of the plate, the acceleration of the flow and the turbulence generation due to the rods and reattachment of the flow seem to contribute to the observed heat transfer augmentation and the heat transfer augmentation increases as the clearance decreases. With wider individual rod the heat transfer coefficient is higher, which is due to the increased acceleration and development of the eddies just before the rods.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.8
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• pp.1022-1030
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• 1999

A numerical study was carried out to analyze the effect of flow distribution of stirred part and plug flow part on combustion efficiency at the coal gasification process in an entrained bed coal reactor. The model of computation was based on gas phase eulerian balance equations of mass and momentum. The solid phase was described by lagrangian equations of motion. The $k-{\varepsilon}$ model was used to calculate the turbulence flow and eddy dissipation model was used to describe the gas phase reaction rate. The radiation was solved using a Monte-Carlo method. One-step parallel two reaction model was employed for the devolatilization process of a high volatile bituminous Kideco coal. The computations agreed well with the experiments, but the flame front was closer to the burner than the measured one. The flow distribution of a stirred part and a plug flow part in a reactor was a function of the magnitude of recirculation zone resulted from the swirl. The combustion efficiency was enhanced with decreasing stirred part and the maximum value was found around S=1.2, having the minimum stirred part. The combustion efficiency resulted from not only the flow distribution but also the particle residence time through the hot reaction zone of the stirred part, in particular for the weak swirl without IRZ(internal recirculation zone) and the long lifted flame.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.6
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• pp.1353-1360
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• 2009

This study examines the effects of internal control system and Analysis of characteristics and Earning management in Vulnerable Cooperation. During research period 2005${\sim}$2007, Purpose of this study is to examines whether financial characteristics has exist or not. Second, Earning management also. As a result of analysis are as follows, First T-test and logistic regression has found explanatory with stastical significance about CURRENT, RNPS, and DEPT. Second, DA of Vulnerable Cooperation is significantly higher than Normal cooperation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.2
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• pp.193-201
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• 1998

A heat exchanging system employing the impinging air jet is still widely used In the various fields due to its inherent merits that include the easiness in engineering applications and the high heat and/or mass transfer characteristics. The purpose of this study is to investigate the enhancement of heat transfer and flow characteristics by placing a turbulence promoters in front of heat exchanging surface. In this study, a series of circular rods are placed at the upstream of a flat plate heat exchanger that is located at potential core region(H/W=2) of a two-dimensional impinging air jet. Heat transfer enhancement is achieved by inserting turbulence promoter that results in the flow acceleration and disturbance of boundary layer. The average Nusselt number of the flat plate with the turbulence promoters is found to be around 1.42 times higher than that of the flat plate without the turbulence promoters. Based on the results of flow visualization with a smoke wire, it is confirmed that the heat transfer enhancement is caused by the flow separation and disturbance of boundary layer by inserting the turbulence promoter.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.11-14
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• 2006

This study investigates the flow field of multiple-jet measured by hot-wire anemometry. The experiments were classified into two cases; 6- or 7-nozzle located circumferentially in equal interval without or with a central jet. The effect of the number of nozzles the flow field was examined when the Reynolds number based on the nozzle diameter is about $10^4$. Mean Velocity, normal and Reynolds stresses were measured in the downstream of jets. The Tollmien's theory holds far downstream at 48d apart from the nozzle exit especially when a nozzle locates at the center. The general flow characteristics is influenced due to the number of nozzles.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.5
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• pp.90-98
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• 2016

A high temperature heater is required to supply high temperature air to the hypersonic propulsion system in order to simulate high velocity flying condition during the ground test. Various high temperature heaters were reviewed, categorized, and analyzed in this paper. Heaters were categorized in 4 groups; in-stream combustion heater, electric arc heater, storage heater, and heat exchange heater. Each group has its own advantages and disadvantages, so the heater should be selected considering its purpose.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.1
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• pp.48-53
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• 2000

The effects of the internal flow in a diesel injection nozzle on the atomization of the spray has been investigated experimentally. Flow visualization was made using a transparent acrylic model nozzle. And also, measurement of the sac chamber pressure was made for clartfying the effect of pressure fluctuation in the sac chamber on the wpray behaviors. The geometry of the model nozzle was scaled up 10 times of the actual nozzle and the injection pressure for the model nozzle was adjusted so as to achieve a Reynolds number at the discharge hole which was the same as the actual nozzle. Polystyrene tracers, a laser sheet light and a still/high speed video camera were used to visualize the flow pattern in the sac chamber. When the needle lift was small, the high turbulence in the sac chamber generated by the high velocity seat flow made the spread angle of the spray large. Cavitation which arose in the sky chamber induced the pressure fluctuation and then affects the spread angle of the spray.

• The Korean Journal of Financial Management
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• v.11 no.1
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• pp.157-169
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• 1994

본 연구는 기업합병매수후 자산매각(資産賣却)이 기업가치에 어떠한 영향을 미치는가를 분석한다. 특히, 기업합병매수후에 자산이 매각될 때의 기업가치에 대한 영향과 기업합병매수와 관련이 없이 자산이 매각될 때의 기업가치에 대한 영향을 비교하여 어떠한 차이가 있는지를 파악하고자 한다. 이러한 분석을 위해 본 연구는 Shleifer와 Vishny(1991)가 정의한 자대매각(資臺賣却)의 유동성비용(流動性費用)(Liquidity Cost of Asset Sale)이라는 개념을 원용하였다. 그들은 자산매각의 유동성비용을 어떤 자산의 급매가치(急賣價値)와 최적활용시(最適活用時) 그 자산이 가져다주는 현금흐름의 순현재가치와의 차이(差異)라고 정의하고 있다. 또한 그들은 어떤 기업이 재무적(財務的) 곤경(困境)에 처해 있을 때 자산매각의 유동성비용이 매우 높다는 것을 보였다. 이러한 개념하에 자산매각이 기업합병매수후 발생할 때 자산매각의 유동성비용이 보다 높은지 여부를 분석하였다. 이를 위해 1982년부터 1989년까지 1,185개의 자산매각 사건들을 합병매수후 자산매각 사건과 합병매수와 관련이 없는 자산매각 사건으로 분류하여 시장위험조정수익률(市場危險調整收益率) 모형(模型)과 시장모형(市場模型)을 이용하여 두표본집단간의 주가변화의 차이를 분석하였다. 그 결과 두집단모두 자산매각에 의해 통계적으로 유의한 정(正)의 초과수익(超過收益)을 보이지만, 기업합병매수후 자산이 매각될 경우가 기업합병 매수와 관련이 없는 경우에 비해 통계적으로 낮은 초과수익을 보이고 있다. 이러한 차이를 본 연구에서는 기업이 합병매수후 겪고 있는 재무적 곤경을 피하기 위해 자산을 신속히 매각하였기 때문에 발생한 유동성 비용이라 해석하고 있다.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.1
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• pp.152-161
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• 2004

The thermal load is a very important problem to be solved in many industrial systems including the electronic equipment. Impinging Jets have been known to provide a large heat transfer rates on surface for many years. The turbulence enhancement of fluid flow is requested for the efficiency elevation of heat transfer. A study on flow fields by rods attached to the wall surface as a promoter of turbulence enhancement has been carried out. The exact analysis on chracteristics of impinging jet field is requested to obtain the optimum design of the impinging jet system. By visualizing the flow field and processing the high digital image by computer PIV can afford exact data on the velocity vector kinetic energy and turbulence intensity in the complex turbulence field. In this study. three kinds of rod shape such as square. triangle. and semicircle are selected as the turbulence promoter. Nozzle diameters are 10mm. 17mm. and 23mm. And the analysis of the flow characteristics due to the above rods is carried out at Re No. 2.000, 3.000. and 4,000 by PIV measurement. It is clarified that the rod setup is very useful to obtain the turbulence enhancement and the turbulence intensity according to the shapes of rod appears large in order of the shapes of rod such as square 〉 triangle 〉semicircle.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.3
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• pp.37-43
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• 2004

Water-jet trajectory visualization and velocity deficits from a high pressurized steam-generator nozzles were experimentally observed. In order to find an optimal nozzle configuration. several parameters affecting plugging and erosion onto the steam generator tube were quantitatively analyzed. For the experiments, a high-pressurized pump (pressure in use: 200 kg/$\textrm{cm}^2$, 15 HP, 11 kW, output flow Q : 301/min) was utilized. Visualization, velocity distribution, and spray growth rate with different nozzle configurations have been mainly focused using a 2-D PDPA system. The results indicated that trajectories along the centerline regardless of their configurations has its potential core region. However, the phenomena from the peripheral part need to be meticulously considered. Accordingly, it is evident that quantitative velocity deficits at the outer region are outstanding due to the aerodynamical drag and entrainment.