• 설비공학논문집
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• 제8권4호
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• pp.561-575
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• 1996

The interaction of turbulent mixed convection and surface radiation in a three-dimensional channel with the heated blocks is analyzed numerically. Two blocks are maintained at high temperature and the other bottom and horizontal walls are insulated. S-4 method is employed to calculate the effect of the radiative heat transfer. The low Reynolds number k-$\varepsilon$ model proposed by Launder and Sharma is used to estimate the turbulent influence on the heat transfer enhancement. From above modeling, the effects of various channel specifications on the flow and heat transfer characteristics are investigated. The variables used for the present study are Reynolds number, block spacing, the channel height spacing for block and the emissivity. Average Nusselt numbers along the block surfaces are correlated and presented in terms of Reynolds number, emissivity and dimensionless geometric parameters. For the range of conditions in this study, average Nusselt numbers along the block surfaces are strongly influenced by the Reynolds numbers and channel height spacing for block but weakly influenced by the block spacing and the emissivity of the adiabatic walls.

• 대한기계학회논문집B
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• 제37권7호
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• pp.647-653
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• 2013

본 연구에서는 산화구리(CuO) 나노분말과 순수 물을 혼합하여 제조한 나노유체를 이용하여 가열된 고체표면에 있어서 나노유체 액적의 증발특성에 대한 실험적 연구를 수행하였다. 실험결과로부터 가열된 표면에서 나노유체 액적의 증발속도는 순수 물 액적보다 증발속도가 약간 증가하는 경향이 있음을 알 수 있었으며, 이는 나노유체에 포함된 나노입자가 유체의 열전도도를 향상시켜 고체 표면에서 액적으로의 열전달이 촉진되었기 때문인 것으로 판단된다. 또한 고체의 표면조도가 커질수록 액적의 증발속도가 약간 증가하였으며, 이는 고체의 표면조도가 커질수록 고체-액체의 접촉 면적이 증가하여 열전달이 촉진되었기 때문인 것으로 추정된다.

• 한국분무공학회지
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• 제12권4호
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• pp.179-184
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• 2007

The boiling heat transfer was experimentally investigated for the FC-77 sprays impacting a square heated test surface in a downward direction. Full cone spray nozzles were employed for the spray cooling experiment, and experiments were made under the test conditions of $Q=3.32{\times}10^{-6}{\sim}2.30{\times}10^{-5}\;m^3/s$, ${\Delta}T_{sub}=20{\sim}70^{\circ}C$. Also, heat transfer measurements were made using the copper block of $10{\times}10\;mm^2$ test area heated by nine cartridge heater. From the experimental results, correlation between the Nusselt number and Reynolds number based on droplet-flow-rate was developed. The correlation shows good predictions with ${\pm}30%$ error for FC-77.

• 대한기계학회논문집B
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• 제32권12호
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• pp.938-944
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• 2008

The boiling heat transfer was experimentally investigated for the PF-5052 sprays impacting a square heated test surface in a downward direction. Full cone spray nozzles were employed for the spray cooling experiment, and experiments were made under the test conditions of Q=$3.32{\time}10^{-6}{\sim}\;12.98{\time}10^{-6}m^3/s$, ${\Delta}T_{sub}=5{\sim}25^{\circ}C$. Also, heat transfer measurements were made using the copper block of $10{\time}10mm^2$ test area heated by nine cartridge heater. From the experimental results, correlation between the Nusselt number and Reynolds number based on droplet-flow-rate was developed. The correlation shows good predictions with ${\pm}30$ % error for PF-5052.

• Journal of Advanced Marine Engineering and Technology
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• 제28권4호
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• pp.624-631
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• 2004

The experimental study on heat transfer characteristics of protruding heated block array as conducted to investigate and to compare the performance of impinging single circular jet in fully developed tube with a twisted tape as a swirl generator. The effects of jet Reynolds number(Re=8700, 13800, 20000. 26500), dimensionless jet-to-block distance(H/d=1. 3, 5. 7) and swirl number(S=0.11, 0.23, 0.30) of the swirl jet on the average Nusselt number for each block and all blocks have been examined. Measurements of heat transfer rate on block surfaces were used naphthalene sublimation technique. Mean velocity and turbulence intensity of the jet along the axis were measured. Potential core length of the jet was 5 times of nozzle diameter because it was fully developed and initially turbulent. With the twisted tape in the nozzle, heat transfer coefficients were higher than those without the twisted tape. which are mainly caused with increasing the jet Reynolds number and swirl number.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2003년도 하계학술대회 논문집
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• pp.47-47
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• 2003

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.63-68
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• 2001

An experimental study was carried out to identify the various regimes of natural convective boiling and to determine the Critical Heat Flux(CHF) on a 70mm square surface which is inclined at $180^{\circ}$(upward), $90^{\circ}, \;45^{\circ}$. The heater block made of copper with cartridge heaters is submerged in a water tank with windows for visualization. As the heat flux increases from $100kW/m^2$ to $1.1MW/m^2$, the heat transfer regime migrates from the nucleate boiling to film boiling and results in a rapid heat up of the heater block. An explosive vapor generation on the heated surface, whose size and frequency are characterized by the heat flux, is visualized by using a digital camcorder with $512{\times}512$ pixel size at 30fps.

• 오토저널
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• 제14권2호
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• pp.76-87
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• 1992

Flow and heat transfer characteristics in a horizontal electronic circuit board are studied numerically. The board has the arrays of heated blocks and the spaces between the plates and blocks are changed. Air in used as cooling fluid, of which prandt1 number is 0.7. The velocity distributions, temperature distributions, Nusselt numbers and dimensionless friction factors are obtained on the spaces between the plates and the blocks, for the cases of Rayleigh number, 0 and 10$^{5}$ . When Rayleigh number is so large, such as 10$^{5}$ , that the effect of bouyancy is not negligible, fluid friction and heat transfer is increased more than those of forced convection. This may be caused by the generation of secondary flow on the cross section of primary flow. The effect of bouyancy is of the most efficient, when the space of blocks is about block-width and the space of plates is about 1.7 times of block-height.

• 한국산학기술학회논문지
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• 제11권2호
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• pp.420-425
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• 2010

온간단조(warm forging) 가공은 가공소재(Billet)를 $800^{\circ}C$ 정도로 가열하여 금형의 다이블록 임프레션(impression) 상면(上面)에 위치결정 시켜 단조하고 있는데, 이 단조가공 과정에서 산화스케일의 비산에 따른 작업자의 화상에 대한 위험도와 산화스케일이 다이블록의 임프레이션에 부착 되거나 열처리기술 미흡으로 금형수명(die life)을 단축시키며 다이블록 안에 분무하는 이형제는 유해먼지, 유해증기, 미스트, 퓸, 악취 등을 발생시켜 작업장 환경을 오염시킴으로써 직무기피 직종으로 분리되기 때문에 생산량 목표 달성에 큰 문제점으로 대두 되고 있다. 더욱이 다이블록의 임프레이션 마멸부위를 수리보수하기 위한 재생공법의 미흡으로 납기지연, 금형비 상승의 요인으로 나타나므로 이에 대한 재생공법 개선과 작업장의 공해물 제거장치의 개발이 요망되고 있다. 본 연구에서는 황동제 관 이음쇠의 온간단조가공에서 도출된 빌릿가열시 문제점, 금형재생 보수시 문제점, 제조원가의 상승요인 등을 외국의 기술과 비교하여 온간단조 금형제작방법개선, 금형재생보수공법 개선, 유해가스 제거장치를 도입하여 환경친화형 작업장 개선 등으로 문제점을 해결 하고자 하였다.

• 한국수산과학회지
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• 제33권4호
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• pp.325-330
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• 2000

갈조류의 주성분인 alginate는 다양한 생리적 기능을 가지고 있으나, 고점성과 난용성으로 인하여 식품에의 광범위한 이용에 제한을 받고 있는 실정이다. Alginate가 가지고 있는 고유의 생리적 기능성을 유지 향상시키면서 점성을 줄이고 용해도를 높혀서 alginate의 이용성을 확대할 목적으로 가열에 의한 저분자화를 시도하였다. 즉, 평균분자량이 약 10,000 (HAG-10), 50,000 (HAG-50) 및 100,000 (HAG-100) 정도의 alginate를 제조하여 각 저분자 atginate의 물리${\cdot}$화학적 특성 변화를 검토하였다. 가열에 의한 점도와 평균분자량은 가열시간이 경과할수록 급격히 저하하였으며, 점도와 평균분자량사이에는 서로 밀접한 상관관계 ($r^2=0.955$)를 나타내었다. 가열에 의한 alginate의 block조성비 및 M/G 비율은 가열시간이 경과함에 따라 MM-block은 변화가 없었으나 GG-block은 급격히 저하하였다. 그리고, MG-block은 오히려 완만히 증가하였으며 M/G 비율은 급격히 증가하는 경향을 보였다. 분자량의 감소에 따른 alginate의 분자구조의 변화를 $FT-IR, ^1H-NMR$ 및 $^(13)C-NMR$로 측정한 결과, 가열에 의해 alginate가 저분자화되어도 분자구조의 특징적인 변화는 관찰할 수 없었다.