• 대한기계학회논문집B
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• 제27권11호
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• pp.1618-1629
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• 2003

The effects of the interaction between flow field and heat transfer caused by the longitudinal vortices are experimentally investigated using a five hole probe and a transient liquid crystal technique. The test facility consists of a wind tunnel with vortex generators protruding from a bottom surface and a mesh heater. In order to control the strength of the longitudinal vortices, the angle of attack of vortex generators used in the present experiment is 20$^{\circ}$, and the spacing between the vortex generators is 25mm. The height and cord length of the vortex generator is 20mm and 50mm, respectively. Three-component mean velocity measurements are made using a f-hole probe system, and the surface temperature distribution is measured by the hue capturing method using a transient liquid crystal technique. The transient liquid crystal technique in measuring heat transfer has become one of the most effective ways in determining the full surface distributions of heat transfer coefficients. The key point of this technique is to convert the inlet flow temperature into an exponential temperature profile using the mesh heater set up in the wind tunnel. The conclusions obtained in the present experiment are as follows: The two maximum heat transfer values exist over the whole domain, and as the longitudinal vortices move to the farther downstream region, these peak values show the decreasing trends. These trends are also observed in the experimental results of other researchers to have used the uniform heat flux method.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 추계학술대회 논문집
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• pp.25-28
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• 2008

Steam reforming reaction is a matured technology to get hydrogen from hydrocarbon fuels compared with other reforming reactions such as partial oxidation(POX), autothermal reforming(ATR). It is so endothermic that it needs heat source to activate the reaction. Due to the reaction characteristics, heat transfer limitation phenomena generally occur in the steam reformer. As one of new ideas, the effect of discontinuous gas feeding is investigated based on heat transfer characteristics. The new operating method is usually favorable at high GHSV region(i.e. over $10,000h^{-1}$). In order to numerically simulate the physical issues, numerical approach is adopted based on heterogeneous reaction model, two-equation model in energy equation, and other constitutive models in porous media.

• 대한기계학회논문집B
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• 제33권7호
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• pp.486-494
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• 2009

One-dimensional modeling of $CH_4$/air premixed flame was conducted to validate the heat loss model and investigate NOx formation characteristics in the postflame region. The predicted temperature and NO concentration were compared to experimental data and previous heat loss model results using a constant gradient of temperature (100 K/cm). The following conclusions were drawn. In the heat loss model using steady-state heat transfer equation, the numerical results using the effective heat loss coefficient ($h_{eff}$) of $1.0\;W/m^2K$ were in very good agreement with the experiments in terms of temperature and NO concentration. On the other hand, the calculated values using the constant gradient of temperature (100 K/cm) were lower than that in the experiments. Although the effects of heat loss suppress NO production near the flame region, a significant difference in NO concentration was not found compared to that under adiabatic conditions. In the postflame region, however, there were considerable differences in NO emission index as well as the contribution of NO formation mechanisms. In particular, in the range of ${\phi}\;{\geq}\;0.8$, the prompt NO mechanism plays an important role in the NO reduction under the adiabatic condition. On the other hand, the mechanism contributes to the NO production under the heat loss conditions.

• 대한기계학회논문집B
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• 제39권7호
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• pp.567-578
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• 2015

Leidenfrost 온도 이상으로 가열된 벽면과 충돌하는 액적의 속도가 열전달 특성에 미치는 영향에 관한 실험 연구를 수행하였다. 동기화된 초고속 가시화 카메라와 적외선 카메라를 이용하여 벽면과 충돌하는 액적의 충돌 특성과 충돌면의 온도 분포를 측정하였다. 획득한 표면온도 분포를 충돌면의 경계 조건으로 이용하여 가열 벽면의 3차원 비정상 열전도 수치해석을 통해 표면 열유속 분포를 얻었다. 수직방향 충돌속도가 증가할수록 최대 액막 직경이 증가하고 가열 벽면과 액막 사이에 존재하는 증기막의 두께가 감소하여 열전달 효율이 증가하였다. 액적은 웨버수가 30보다 작은 경우 되튐현상이 발생하였으며, 큰 경우 작은 액적들로 분쇄되어졌다. 충돌속도에 의한 열전달량의 증가 경향이 되튐영역에서 분쇄영역에서 가면서 약화되었으며, 이는 분쇄현상에 의해 유효 열전달 면적의 확대 효과가 저감되었기 때문으로 해석된다.

• 한국유체기계학회 논문집
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• 제18권3호
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• pp.38-45
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• 2015

In this study, two computational methodologies were compared to consider an effective conjugate heat transfer analysis technique for the cooled vane with thermal barrier coating. The first one is the physical modeling method of the TBC layer on the vane surface, which means solid volume of the TBC on the vane surface. The second one is the numerical modeling method of the TBC layer by putting the heat resistance interface condition on the surface between the fluid and solid domains, which means no physical layer on the vane surface. For those two methodologies, conjugate heat transfer analyses were conducted for the cooled vane with TBC layer having various thickness from 0.1 mm to 0.3 mm. Static pressure distributions for two cases show quite similar patterns in the overall region while the physical modeling shows quite a little difference around the throat area. Thermal analyses indicated that the metal temperature distributions are quite similar for both methods. The results show that the numerical modeling method can reduce the computational resources significantly and is quite suitable method to evaluate the overall performance of TBC even though it does not reflect the exact geometry and flow field characteristics on the vane surface.

• 대한기계학회논문집A
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• 제38권4호
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• pp.427-436
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• 2014

이 연구에서는 STD61 열간금형강 상부에 생성되는 하드페이싱층에 적합한 하드페이싱 재료와 두께를 3 차원 비정상 열전달 및 열응력 해석을 통하여 예측하고자 한다. Stellite6, Stellite21과 19-9DL 초합금을 하드페이싱 재료로 적용하였다. 하드페이싱 재료와 두께가 하드페이싱된 시편 내부 온도, 열응력 및 변형률 분포 변화에 미치는 영향에 대하여 분석하였다. 이 결과로부터 큰 열전도도를 가지는 재료로 얇은 하드페이싱 층을 생성하는 것이 열전달 특성 측면에서는 효과적인 것을 알 수 있었다. 또한, Stellite21 초합금으로 2 mm 두께의 하드페이싱부를 STD61 열간 금형강 상부에 생성할 경우, 하드페이싱부와 기저부의 경계부에서 유효응력 및 주변형률 편차가 최소화됨을 알 수 있었다. 이 결과들로부터 STD61 열간금형강에 적합한 하드페이싱 재료와 두께를 예측할 수 있었다.

• 자원환경지질
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• 제17권2호
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• pp.109-114
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• 1984

The geophysical implications of the observed heat flow in the Korean Peninsula are examined. The Peninsula can be devided into two typical regions of high (Zone 1) and normal heat flows (Zone 2), and anomalous sharp change of heat flow between two zones is noteworthy. Zone 1 (southeastern coast of the Peninsula) to be connected to the East Sea (=Japan Sea) of high heat flow region corresponds with the region of late-Mesozoic to Tertiary igneous activity. With the radioactive elements concentrated in the crust, the observed heat flow in Zone 2 can be almostly explained. While, only a half of the heat flow in Zone 1 is explained. As a possible explanation of high heat flow in Zone 1, partial melting in the lower crust is examined. The temperature of $800-900^{\circ}C$ calculated at the bottom of the crust excludes the possibility of partial melting or magma generation in the crust. Alternatively, a remaining thermal effect of late-Mesozoic to Tertiary igneous activity is considered. However, it appears that the thermal effect already disappeared and that the vertical temperature distribution reached at steady state 30 MY ago (= 10 MY after the igneous activities came to an end). After all, the existence of some other effective heat transfer in Zone 1 is strongly suggested. The high heat flow to be same kind of anomalous one of the East Sea can be recognized as a result of the trench-back-arc thermal flux. The plate subduction in the Japan Trench will generate an induced flow above the slab of the East Sea, a typical back-arc basin, and hence the induced flow will heat the surrounding lithosphere.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume II
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• pp.1001-1002
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• 2006

Special problem emphasized by specialists in the field of analyzing the heat interchanges in the system ocean-atmosphere (SOA) is a necessity of determination of the near-surface atmospheric temperature, which can be only indirectly connected with characteristics of the SOA natural microwave radiation measured from satellites. That is why, the following dilemma is not obvious, but interesting and promised: what is better - to use the satellite methods for retrieving the partial parameters of the SOA or for analysis its state as a whole. To our opinion, this task is similar to the idea recognized by specialists engaged in the heat infrared region (8-12 mcm) of electromagnetic spectrum and its applications, where an intensity of natural infrared radiation (effective radiation) is used as the inherent property (the attribute) of the SOA heat balance. Here we studied important aspects of this problem: a) what medium initiates a heat transfer in the SOA and disturbs its heat balance - the ocean or the atmosphere b) what SOA parameters directly influence on its natural microwave radiation intensity (brightness temperature) measured from satellites? We relate these processes mainly to the synoptic range of time scales enriched by various events in the SOA interface such as the mid-latitude and tropical cyclones.

• Ocean Systems Engineering
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• 제2권1호
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• pp.17-31
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• 2012

This study investigated the behavior of a non-isothermal $CO_2$ bubble formed through a leak process from a high-pressure source in a deep sea. Isenthalpic interpretation was employed to predict the state of the bubble just after the leak. Three modes of mass loss from the rising bubble were demonstrated: dissolution induced by mass transfer, condensation by heat transfer and phase separation by pressure decrease. A graphical interpretation of the last mode was provided in the pressure-enthalpy diagram. A threshold pressure (17.12 bar) was identified below which the last mode was no longer present. The second mode was as effective as the first for a bubble formed in deep water, leading to faster mass loss. To the contrary, only the first mode was active for a bubble formed in a shallow region. The third mode was insignificant for all cases.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2011년도 춘계학술발표대회 논문집
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• pp.144-149
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• 2011

This study aims to evaluate performance of ventilation and thermal about breathing wall by flowing air to indoor on appropriate conditions that is effective aperture area in the Central region(20, 50, $80cm^2/m^2$). The result is as follows : 1) Sectional temperature distribution of inflow and outflow out under the constant ventilation was reviewed. In the case of inflow, outside temperature increase effect was confirmed. 2) The more differences of temperature between outdoor and indraft of air was high, the more heat recovery was high.