• 열처리공학회지
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• 제23권5호
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• pp.249-256
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• 2010

Water jet impingement cooling has been widely used in a various engineering applications; especially in cooling of hot steel plate of steelmaking processes and heat treatment in hot metals as an effective method of removing high heat flux. The effects of cooling water temperature on water jet impingement cooling are primarily investigated for hot steel plate cooling applications in this study. The local heat flux measurements are introduced by a novel experimental technique that has a function of high-temperature heat flux gauge in which test block assemblies are used to measure the heat flux distribution during water jet impingement cooling. The experiments are performed at fixed flow rate and fixed nozzle-to-target spacing. The results show that effects of cooling water temperature on the characteristics of jet impingement heat transfer are presented for five different water temperatures ranged from 5 to $45^{\circ}C$. The local heat flux curves and heat transfer coefficients are also provided with respect to different boiling regimes.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.68-73
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• 2006

The present paper deals with an experimental study of boiling heat transfer characteristics of R-290, and is focused on pressure gradient and heat transfer coefficient of the refrigerant flow inside horizontal smooth minichannel with inner diameter of 3.0 mm and length of 2000 mm. The direct heating method applied for supplying heat to the refrigerant where the test tube was uniformly heated by electric current which was applied to the tube wall. The experiments were conducted with R-290 with purity of 99.99% at saturation temperature of 0 to $10^{\circ}C$. The range of mass flux is $50{\sim}250kg/m^2s$ and heat flux is $5{\sim}20kW/m^2$. The heat transfer coefficients of R-290 increases with increasing mass flux and saturation temperature, wherein the effect of mass flux is higher than that of the saturation temperature, whereas the heat flux has a low effect on increasing heat transfer coefficient. The significant effect of mass flux on heat transfer coefficient is shown at high quality, the effect of heat flux on heat transfer coefficient at low quality shows a domination of nucleate boiling contribution. The heat transfer coefficient of the experimental result was compared with six existing heat transfer coefficient correlation. Zang et al.'s correlation(2004) gave the best prediction of heat transfer coefficient.

• 한국화재소방학회논문지
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• 제17권4호
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• pp.117-123
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• 2003

본 연구에서는 Setchkin 착화성시험장치와 산소소비원리를 이용한 콘칼로리미터를 사용하여 난연처리되지 않은 경질우레탄폼의 착화특성 및 열방출특성 및 플래쉬오버 가능성에 대하여 연구하였다. 연구결과 경질폴리우레탄폼의 유도발화온도(FIT)는 $383^{\circ}C$∼$390^{\circ}C$, 자연발화온도(SIT)는 $493^{\circ}C$∼$495^{\circ}C$로 나타났으며 자연발화온도가 유도발화온도에 비해 약 $100^{\circ}C$ 높게 나타났다. 콘칼로리미터실험에서는 착화시간은 heat flux의 크기가 증가할수록 빨라졌으며 동일한 heat flux 크기에서는 밀도가 작을수록 착화시간은 짧게 나타났다. 열방출율은 $50 ㎾\m^2$에서 가장 크게 나타났으며, 최대열방출율의 경우 heat flux의 크기와 밀도가 커질수록 증가하는 경향을 보였다. 착화시간과 열방출율의 관점에서 경질폴리우레탄폼의 화재성능은 가해진 heat flux의 크기와 밀도에 큰 영향을 받는 것으로 나타났으며, Petrella의 제안방법에 의해 플래쉬오버 가능성을 분류한 결과 플래쉬오버 가능성이 큰 것으로 분류되었다.

• Ocean and Polar Research
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• 제26권3호
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• pp.453-463
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• 2004

The Antarctic Peninsula is important in terms of global warming research due to pronounced increase of air temperature over the last century. The first eddy covariance system was established at King Sejong Station located in the northern region of the Antarctic Peninsula in December of 2002 and has been operated over one year. Here, we analyze turbulent characteristics to determine quality control criteria for turbulent sensible heat flux data as well as to diagnose the possibility of long term eddy covariance measurement under extreme weather conditions of the Antarctic Peninsula. We also report the preliminary result on sensible heat flux. Based on the analyses on turbulent characteristics such as integral turbulence characteristics of vertical velocity (w) and heat (T), stationarity test and investigation of correlation coefficient, they fallow the Monin-Obukhov similarity and eddy covariance flux data were reliable. ${\sim}47%$ of total retrieved sensible heat flux data could be used for further analysis. Daytime averaged sensible heat flux showed a pronounced seasonal variation, with a maximum of up to $300Wm^{-2}$ in summer. In conclusion, continuous and long-term eddy covariance measurement may be possible at the study site and the land surface may influence the atmosphere significantly through heat transport in summer.

• 동력기계공학회지
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• 제18권1호
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• pp.106-111
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• 2014

This article describes effect of post heat treatment on wear characteristics of thermally sprayed Co-based self-flux alloy coating. Co-based self-flux alloy coatings were deposited on steel substrates using a flame spray process. Post heat treatments were carried out at 800, 900, 1000 and $1100^{\circ}C$ for 30min in a vacuum chamber. For analysis of effect of post heat treatment on mechanical properties, wear test and hardness test were performed for post heat-treated coating specimen. Microstructures of heat treated coating layer and wear track were examined using SEM and EDS. Wear loss and hardness became lower with increasing post heat treatment temperature.

• 설비공학논문집
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• 제10권1호
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• pp.22-32
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• 1998

Separate type thermosyphon has larger critical heat flux than non-loop type thermosyphon, because the flooding phenomenon of vapor and liquid occurring in non-loop one does not occur. The experimental study has been carried out separate type thermosyphon with single tube. An investigation of heat transfer characteristics in separate type thermosyphon is performed experimentally. Heat transfer coefficients in an evaporator and condenser were measured experimentally. The effects of liquid filling ratio, height difference, cooling temperature and heat flux on the heat transfer coefficients were examined. As a result, the reasonable range of the liquid filling ratio and the dependence of heat transfer on vapor temperature and heat flux are obtained.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.30-33
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• 2005

Though sensible heat flux is one of heat flux components, it is generally considered that the importance is low compared with other components because of the small value. Actually sensible heat flux over the tropical ocean is extremely small, less than $100\;W/m^2$ .. However, it should be noted that sensible heat flux in boreal winter over the western boundary current regions is considerably large, about $100\;W/m^2$, and not neglected. In this study we carry out intercomparison of various global sensible heat flux data including not only satellite-derived data but also reanalysis data in order to clarify the characteristics of those data.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.644-648
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• 2002

Though it was difficult of globally monitor latent heat flux aver the ocean for many years, the situation is rapidly changing by the use of satellite data. Since a bulk formula is used to estimate turbulent heat flux using satellite data, we need wind speed, sea surface temperature and specific humidity data. However, it is not easy to accurately estimate specific humidity using satellite data. Now several algorithms for estimating specific humidity have been proposed and applied to construct latent heat flux data sets. Latent heat flux data sets derived from satellite data such as J-OFURO, HOAPS and GSSTF are available at present. Since the algorithm and used satellite data are not the same between them. the characteristics of each data set may be different. Therefore, it is important to clarify the difference between each data set and investigate the cause of the difference in latent heat flux estimates. In this paper we summarize the present state of the art with regard to the turbulent heat flux estimation by using satellite data. Also we present the comparison results of latent heat flux fields including not only satellite-derived flux fields but also analysis fields.

• 한국가시화정보학회지
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• 제22권1호
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• pp.6-17
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• 2024

This study examined the natural convection heat flow characteristics of the melting process of PCM (palm oil) inside a liquid flexitank(bag) for a cargo container. A film heating element was installed on the bottom of the container, and numerical analysis was performed under heat flux conditions of 1,000 to 4,000 W/m². As a result, the melt interface of the PCM rises to a nearly horizontal state over time. In the initial stage, conduction heat transfer dominates, but gradually waves at the cell flow and melt interfaces are formed due to natural convection heat transfer. As melting progresses, the Ra number increases parabolically, and the Nu number increases linearly and has a constant value. The Nu number rises slowly under low heat flux conditions, whereas under high heat flux conditions, the Nu number rises rapidly. As the heat flux increases, the internal temperature oscillation of the liquid phase after melting increases. However, under high heat flux conditions, excess heat exceeding the latent heat is generated, and the temperature of the molten liquid is raised, so the increase in melting rate decreases. Therefore, the appropriate heating element specification applied to a 20-ton palm oil container is 2,000 W/m².

• 한국환경과학회지
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• 제3권1호
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• pp.17-29
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• 1994

An one dimensional atmosphere-vegetation interaction model is developed to discuss of the effect of vegetation on heat flux in mesoscale planetary boundary layer. The canopy model was a coupled system of three balance equations of energy, moisture at ground surface and energy state of canopy with three independent variables of $T_f$(foliage temperature), $T_g$(ground temperature) and $q_g$(ground specific humidity). The model was verified by comparative study with OSUID(Oregon State University One Dimensional Model) proved in HYPEX-MOBHLY experiment. As the result, both vegetation and soil characteristics can be emphasized as an important factor iii the analysis of heat flux in the boundary layer. From the numerical experiments, following heat flux characteristics are clearly founded simulation. The larger shielding factor(vegetation) increase of $T_f$ while decrease $T_g$. because vegetation cut solar radiation to ground. Vegetation, the increase of roughness and resistance, increase of sensible heat flux in foliage while decrease the latent heat flux in the foliage.