• 대한기계학회논문집B
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• 제26권4호
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• pp.622-628
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• 2002

Numerical analysis has been carried out for two-dimensional steady and unsteady mixed convection in the annulus between co-rotating horizontal cylinders with a heated inner cylinder. The ratio of annulus gap($\sigma$) is taken from 1 to 10 and the order of mixed-convection parameter B(=Gr/(1+Re)$^2$) varies from 10$^4$to $10^0$. The flow patterns over this parameter range are steady multicellular, oscillatory multicellular or steady unicellular. The addition of co-rotating of both cylinders stabilizes the flow in the annulus and weakens the unsteadiness. Even in the large values of rotating parameter such as of $10^0$/($\sigma$=2) and 10$^2$($\sigma$=10), the flow pattern becomes asymptotic to the steady unicellular flow, like as in the rigid-body rotating flow.

• Journal of Mechanical Science and Technology
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• 제16권5호
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• pp.647-654
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• 2002

This study deals with the characteristic of quenching refrigerant for heat treatment deformation control of SM45C steel. Heat-treatment deformation must be controlled for the progress of production parts for landing gear. Most of deformation is occurred on inconsistent cooling. The inconsistent cooling is caused by a property of quenching refrigerant. When a heated metal is deposited in the quenching refrigerant, the cooling speed is so slow in early period of cooling because of a steam-curtain. After additional cooling, the steam-curtain is destroyed. In this progress, the cooling speed is very fast. The object of this study is to control the deformation of heat-treatment for landing gear by improving the conditions of quenching. The cooling curves and cooling rates of water, oil and polymer solution are obtained and illustrated. From the characteristics of the quenching refrigerant, the effects of heat-treatments on thermal deformation and fatigue strength are also investigated.

• 대한기계학회논문집B
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• 제26권1호
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• pp.141-149
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• 2002

A numerical simulation is performed for the cooling heat transfer of a heated cylindrical pedestal by an axisymmetric jet impingement. Based on the k- $\varepsilon$- f$\sub$${\mu}$/ model of Park et at., the linear and nonlinear stress-strain relations are extended. The Reynolds number based on the jet diameter(D) is fixed at Re$\sub$D/ = 23000. The local heat transfer coefficients are compared with available experimental data. The predictions by k- $\varepsilon$-f$\sub$${\mu}$/ model are in good agreement with the experiments, whereas the standard 7- f model does not properly resolve the flow structures.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 초전도 자성체
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• pp.14-16
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• 2002

Melting and re-solidification nature of $SmBa_2Cu_3O_{7-y}$ (Sm123) grains in Ba-Cu-O (Ba:Cu=3:5) liquid containing 0.7 at.% yttrium were investigated at the temperature lower than its melt point. When Sm123 grains/liquid powder compacts were heated to a temperature between two melting points of Ba-Cu-O liquid ($1000^{\circ}C$) and a Sm123 phase ($1060^{\circ}C$) and held at this temperature for appropriate time, Sm123 grains melted partly in the liquid that was formed by melting of the liquid-forming powder. During subsequent slow cooling, (Sm,Y)$Ba_2Cu_3O_{7-y}$ solidified at the outer parts of the unmelted Sm12 grains, which is distinguished from the core regions by lower $Sm_2BaCuO_5$ (211) density.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2005년도 동계학술발표대회 논문집
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• pp.300-305
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• 2005

The present experimental study investigates single-phase heat transfer coefficients downstream of support grid in $6{\times}6$ rod bundles. Support grid with split mixing vanes enhance heat transfer in rod bundles by generating it make turbulence. But this turbulence is confined to short distance. Support grid with LSVF mixing vanes enhanced heat transfer to longer distance. The corresponding Reynolds number investigated in the present study is Re=30,000. The heat transfer coefficients are measured using heated and unheated copper sensor.

• 한국초전도ㆍ저온공학회논문지
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• 제21권4호
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• pp.44-47
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• 2019

This paper is a study of recovery under load process of superconducting fault current limiter (SFCL). SFCL consists of five parallel-connected high-temperature superconductor (HTS) tapes additionally stabilized by stainless tape. Previously, HTS was heated by current pulse to simulate a short circuit in a power grid. During the cooling period, the current amplitude decreased to 23% or less of HTS critical current value, which is the simulation of network re-switching. When HTS with a polymer coating is cooled, temperature gradient on thermal insulation layer occurs, that prevents a boiling crisis and improves the heat sink into liquid nitrogen. Two samples are coated with a 30 ㎛ and 50 ㎛ polylactide (PLA) layers, reference sample has no polymer coating on it. Samples with a polymer coating show 3-5 times faster cooling than the reference one.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2210-2213
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• 2008

In the present study, effects of degree of confinement on heat transfer characteristics of a micro-scale slot jet impinging on a heated flat plate are experimentally investigated. The effects of Reynolds numbers (Re = $1000{\sim}5000$), lateral distances (x/B = $1{\sim}10$), nozzle-to-plate spacings (Z/B = $1{\sim}20$), and degree of confinement ($B_c$/B = 3, 48) on the Nusselt number are considered. The results show that the effects of the degree of confinement on the cooling performance of the micro-scale impinging slot jet are significant at lower nozzle-to-plate spacings and higher Reynolds numbers. In addition, it is shown that the cooling performance of the micro-scale unconfined slot impinging jet is 200% higher than that of the micro-scale confined slot impinging jet.

• 대한설비공학회지:설비저널
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• 제16권2호
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• pp.185-193
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• 1987

The heat transfer characteristics from a solid sphere in a fluctuating air flow is simulated numerically in the range of the Reynolds numbers, $1\;{\leqslant}\;Re\;{\leqslant}\;40.$ Such a situation may be encountered in forced convection from a heated spherical particle in a sound field or oscillat-ing flow. The amplitude and phase delay in the heat transfer response to the flow oscillation are computed for a small amplitude flow. The instantaneous response of heat transfer is simulated for the large amplitude oscillation and compared with the quasi-steady response. The effect of the oscillation on the time - mean value in the local and overall heat transfer rate is discussed along with the change in the flow .field.

• KSBB Journal
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• 제10권4호
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• pp.449-454
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• 1995

대두유 및 미강유의 찌꺼기유내에 존재하는 고부가가치의 토코페롤을 농축하기 위하여, 찌꺼기유중의 불포화 유라지방산의 제거에 에타서l시스반응을 적용하고 그에 따른 농축효과에 관하여 연구하였다. 함유된 스테롤은 흔합용매법에 의해 제거하였고, 메타세시스반응은 헬륨분위기의 회분삭반응기를 사용하였다. 대두유 및 미강유의 찌꺼기유에 함유되어 있는 토코페롤은 헥산용매중에서 또는 공기존재하에서 가열하면 쉽게 소실되었다. 스테롤을 제거한 여액의 에타세시스반응에 있어서, 사용한 $Re_2O_7/Al2O_3$ 촉매는 12.8% (w/w)의 담지율이 가장 좋았는데, 이는 고담지율에서의 [$Re_2O_7$]과 테트라에틸주석이 반응하여 메타세시스에 유효한 활생종을 생성하기 때문으로 생각되었다. 촉매량은 원액 109당 O.5g의 경우가 최적이었으며, 반응온도는 $25^{\circ}C$가 가장 좋았다. 이 사살들로부터 찌꺼기유중의 토코페롤을 새로운 메타세시스반응에 의해 고농도로 항축할 수 있음을 알 수 있었다.

• Journal of Ginseng Research
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• 제32권2호
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• pp.127-134
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• 2008

This study was carried out to investigate the changes of ginsenosides composition in Korean red ginseng water extract (RGWE) after heated with high temperatures above $100^{\circ}C$. RGWEs were adjusted with pH 3.0, pH 7.0 and pH 10.0, respectively, and then heated at 100,110 and $120^{\circ}C$ for 30 minutes by using autoclave. Total ginsenosides of RGWE treated with heating showed decreasing tendency when compared with control. By TLC analysis, decreasing effect of ginsenosides in RGWE were significantly observed in the acidic condition of pH 3.0, particulary. By HPLC analysis, total ginsenoside of control showed 1.89%, while those of RGWE treated with 100, 110 and $120^{\circ}C$ showed 1.22, 1.05 and 0.97%, respectively. The ratio of protopanaxadiol (PD) to protopanaxatriol (Pr) saponins in control was 1.89, while that of PD/PT in treated RGWEs were level of 1.33 to 1.47. By the result of decreased ratio of PD/PT in RGWE, it was considered that PD type saponin such as ginsenoside$-Rb_{1}$, $-Rb_{1}$, -Rc and -Rd was more unstable than PT type saponin such as ginsenoside-Re and Rg against high temperature heating above $100^{\circ}C$.