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함진기(Jin-KI Ham),김영기(Young-Ki Kim),이희원(Hee-Won Lee),김진수(Jin-Soo Kim),송석현(Seok-Hyun Song) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
The thermal design of the bus bur of a Gas-Insulated Switchgear(GIS) becomes important since the current-carrying capacity of the GIS is limited by maximum operating. In order to predict temperature rise of the bus bar, a program has been developed. Various heat sources possibly generated in the bus bar are calculated in the program. To estimate temperature rises at the bus bar caused by the heat balance between the heat generation and heat transfer, the finite volume method as well as the 4th order Runge-Kutta method has been employed. In the experiment, temperature rises at conductor, contast part and external tank are measured for full-scale gas-insulated bus bars. The comparisons of the predicted values of balance calculation to the experiments are made. From the comparisons. it is conaluded that the developed program can predict the temperature rise of the bus bar quite well.
가스절연 변압기용 열교환기의 열전달 및 압력손실 특성 연구
함진기(Jin-Ki Ham),이준엽(Joon-Yeob Lee),김영기(Young-Ki Kim),송석현(Seok-Hyun Song) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
A plate-fin-tube heat exchanger used for a SF6 gas-insulated transformer is extremely important since the dissipation of the heat generated from inside coils has a significant effect on the performance as well as the durability of the transformer. The heat exchanger consists of corrugated plate fins and staggered array tube bundles for coolant. In order to find out heat transfer and pressure drop characteristics, series of numerical analyses for plate fins with enhanced surface geometries were conducted. Based on the results of the numerical analyses, an improved model of the plate fin has been proposed.
전기자동차용 Cold Plate의 열전달 및 압력손실 특성 연구
함진기(Jin-Ki Ham),이준엽(Joo-Yeob Lee),송석현(Seok-Hyun Song) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
The cold plate used for a CEU(Control Electronics Unit) of an EV(Electric Vehicle) is extremely important since the dissipation of the heat generated from power devices like IGBT(Insulated Gate Bipolar Transistor) and diode has a significant effect on the performance as well as the durability of the CEU. The cold plate consists of seven power devices, and coolant flows through the passage bonded to a groove of the cold plate. In order to find out heat transfer and pressure drop characteristics, series of numerical analyses for the cold plate with enhanced coolant passages were conducted. Based on results of the numerical analyses, an improved model of the cold plate has been proposed. The experiments under the varioius conditions have been conducted to compare the performance of the proposed cold plate to the present one. As a result of the numerical analyses together with the experiments, the ideal design of the cold plate could be offered.
냉각유로방식 변화에 따른 슬롯 막냉각에서의 유동 및 열전달 특성
함진기,조형희,Ham, Jin-Ki,Cho, Hyung-Hee 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.6
An experimental investigation is conducted to improve a slot film cooling system which can be used for the cooling of gas turbine combustor liner. The tangential slots are constructed of discrete holes with different injection types which are the parallel, vertical, and combined to the slot lip. The investigation is focused on the coolant supply systems of normal-, parallel-, and counter-flow paths to the mainstream direction. A naphthalene sublimation technique has been employed to measure the local heat/mass transfer coefficients in a slot with various injection types and coolant feeding directions. The velocity distributions at the exit of slot lip for the parallel and vertical injection types are fairly uniform with mild periodical patterns with respect to the hole positions. However, the combined injection type increases the nonuniformity of flow distribution with the period equaling twice that of hole-to-hole pitch due to splitting and merging of the ejected flows. The secondary flow at the lip exit has uniform velocity distributions for the parallel and vertical injection types, which are similar to the results of a two-dimensional slot injection. In the results of local heat/mass transfer coefficient, the best cooling performance inside the slot is obtained with the vertical injection type among the three different injection types due to the effect of jet impingement. The lateral distributions of Sh with the parallel- and counter-flow paths are more uniform than the normal flow path. The averaged Sh with the injection holes are $2{\sim}5$ times higher than that of a smooth two-dimensional slot path.
고속 회전체용 가스 포일 스러스트 베어링의 하중지지력 및 마찰손실 해석을 위한 유체-구조 연성해석
최문호(Moo Ho Choi),이준호(Jun Ho Lee),함진기(Jin Ki Ham) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
A novel fluid-solid interaction (FSI) model was developed to evaluate load carrying capacity (LCC) and frictional power loss for gas-lubricated, compliant surface radial foil thrust bearings. The FSI model consists of coupled hydrodynamic and static structure analysis model. The hydrodynamic model received pressure distribution and film thickness onto the deformed thrust bearing surface. Then the hydrodynamic analysis code solved compressible Reynolds equation using finite element method to obtain iterative solution of periodic pressure distribution. The hydrodynamic analysis model was verified by comparing the solution with those obtained by computational fluid dynamics package in the rigid bearing surface. The structural analysis was conducted with commercial finite element analysis package considering the present state-of-the-art techniques used in foil bearing analysis. The analysis model in this research was compared with previous experimental data and correlations taken at a fixed film thickness and a rigid bearing. Then the correlations were modified in order to express the LCC and the power loss considering the periodic pressure distribution and the deformation of the top foil.
배플 구조에 따른 원통다관형 열교환기의 열전달 특성에 관한 수치해석적 연구
백원계(Won Kye Baek),이성원(Seong Won Lee),함진기(Jin Ki Ham),고준호(Joon Ho Ko) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
Numerical analyses have been performed on a LNG(Liquefied Natural Gas) heat exchanger of the FGSS(Fuel Gas Supply System) of Hyundai Heavy Industries. A type of LNG heat exchanger currently used in FGSS is shell and tube heat exchanger which has been widely used in industrial applications. Material properties variation of the natural gas inside the heat exchanger depending on the temperature has been considered on the numerical analyses. Performance of the heat exchanger is improved by controlling baffle spacing and height, and reduction of pressure drop is verified when the baffle is rotationally periodic structure. It is because the shell-side flow is not zigzag flow but spiral flow. Although the reduction of the pressure drop results in lowering the heat transfer efficiency, it appears that if the rotational angle of baffle becomes smaller, the pressure drop decreases. Accordingly, the rotational baffle leads to higher heat transfer efficiency at the same pressure drop of a general heat exchanger with existing horizontal baffle.
선박 폐열회수용 핀-튜브 열교환기의 열전달 및 마찰 인자에 관한 수치해석적 연구
백원계(Won Kye Baek),하정훈(Jung Hoon Ha),함진기(Jin Ki Ham) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
Numerical analyses were performed to calculate the heat transfer and friction factor of a finned-tube heat exchanger used for exhaust gas boiler in ships. The heat exchanger has two main design constraints. The first constraint is velocity lower limit to prevent soot of exhaust gas from being deposited. And the second constraint is permissible pressure loss in order to forbid increase of back-pressure which may lead to a high thermal loading of engine components. Based on those reasons, tubes of the boiler have to be arranged in-line so as to decrease amounts of soot deposition. And the tube-diameter of the boiler has to be larger than that of prevalent finned-tube heat exchanger. In this study, the heat transfer and flow friction factor of the presented finned-tube heat exchanger were correlated using computational fluid dynamics since the existing heat transfer and friction correlations are not valid for such a large tube-diameter with in-line arrangement. Number of tube rows was firstly considered because the exhaust gas boiler has formulaic specification as mentioned earlier. The correlation formulas which were obtained from the computational analyses can be used for further studies such as performance prediction or geometrical optimization.