• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.11
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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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• 2008.10a
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.7
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• pp.567-578
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• 2015

Single droplet-wall collision heat transfer characteristics on a heated plate above Leidenfrost temperature were experimentally investigated considering the effects of impact velocity. The collision characteristics of the droplet impinged on the heated wall and the changes in temperature distribution were simultaneously measured using synchronized high-speed video and infrared cameras. The surface heat flux distribution was obtained by solving the three-dimensional transient heat conduction equation for the heated substrate using the measured surface temperature data as the boundary condition for the collision surface. As the normal impact velocity increased, heat transfer effectiveness increased because of an increase in the maximum spreading diameter and a decrease in the vapor film thickness between the droplet and heated wall. For We < 30, droplets stably rebounded from a heated wall without breakup. However, the droplets broke up into small droplets for We > 30. The tendency of the heat transfer to increase with increasing impact velocity was degraded by the transition from the rebounding region to the breakup region; this was resulted from the reduction in the effective heat transfer area enlargement due to the breakup phenomenon.

• The KSFM Journal of Fluid Machinery
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• v.18 no.3
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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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.4
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• pp.427-436
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• 2014

The goal of this paper is to estimate proper hardfacing material and thickness of STD61 hot-working tool steel through three-dimensional heat transfer and thermal stress analyses. Stellite6, Stellite21 and 19-9DL superalloys are chosen as alternative hardfacing materials. The influence of hardfacing materials and thicknesses on temperature, thermal stress and thermal strain distributions of the hardfaced part are investigated using the results of the analyses. From the results of the investigation, it has been noted that a hardfacing material with a high conductivity and a thinner hardfaced layer are desired to create an effective hardfacing layer in terms of heat transfer characteristics. In addition, it has been revealed that the deviation of effective stress and principal strain in the vicinity of the joined region are minimized when the Stellite21 hardfaced layer with the thickness of 2 mm is created on the STD61. Based on the above results, a proper hardfacing material and thickness for STD61 tool steel have been estimated.

• Economic and Environmental Geology
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• v.17 no.2
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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.

• Proceedings of the KSRS Conference
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• v.2
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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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• v.2 no.1
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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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• 2011.04a
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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.