• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.10
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• pp.1363-1370
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• 1997

Single liquid droplet combustion processes including heating, evaporation, droplet burning and flame radiation were theoretically investigated by adopting nongray gas radiation model for the radiative transfer equation (RTE). n-Heptane was chosen as a fuel and the numerical results were compared with the experimental data available in the literature. The discrete ordinate method (DOM) was employed to solve the radiative transfer equation and the weighted sum of gray gases model (WSGGM) was applied to account for nongray effect by CO$_{2}$, and H$_{2}$0. Therefore, detailed effects by nongray gas and its comparison with the gray gas model could be figured out in the results. It is found that the radiative heat flux is higher when the nongray model is used, thereby reducing the maximum gas temperature and the flame thickness, but the total burning time increases due to the deceased conductive heat flux in nongray model. Consequently, a better agreement with experimental data could be obtained by using nongray model.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.3
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• pp.213-219
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• 2008

Microscale heat transfer and microfluidics have become increasingly important to overcome some very complex engineering challenges. The use of very small passages to gain heat transfer enhancement is a well documented method for achieving high heat flux dissipation. In this study, the performance evaluation of micro-channel plated heat exchangers with straight, V-shaped and Y-shaped channels has been experimentally carried out under the counterflow condition. It is found that the mixing effect in V-shaped and Y-shaped channels enhances the heat transfer but pressure drop does not increase seriously in the range of low Reynolds number.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.1
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• pp.54-61
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• 1999

The fully developed turbulent momentum and heat transfer induced by the roughness elements on the outer wall surfaces in concentric annuli are analytically studied on the basis of a modified turbu-lence model. The resulting momentum and heat transfer are discussed in terms of various parame-ters such as the radius ratio the roughness density Reynolds number and Prandtl number accord-ing to the heating condition. The study shows that certain artificial roughness elements may be used to enhance heat transfer rates with advantage from the overall efficiency point of view.

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.2
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• pp.36-43
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• 2001

In order to understand the laminar heat transfer enhancement by swirl flow, the effects of heat transfer in a circular pipe with twisted inserts are investigated experimentally. In the present study, a uniform heat flux condition is considered. Laminar heat transfer correlations are developed using least square fit method from surface temperature distributions of an electrically-heated pipe and flow properties. Average Nusselt number correlations with twisted inserts are expressed as a function of swirl parameter, Reynolds number and prand시 number. When the twisted ratio is 6.50, mean Nusselt number and friction factor increase by approximately 500% and 300%, respectively, compared with the values for a pipe without inserts.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.229-234
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• 2007

Microscale heat transfer and microfluidics have become increasingly important to overcome some very complex engineering challenges. The use of very small passages to gain heat transfer enhancement is a well documented method for achieving high heat flux dissipation. As the passage size is decreased, the heat transfer performance increases but the pressure drop increases sharply when the passage size is reduced. In this study, the performance evaluation of micro plated heat exchangers under the counter flows with straight, V-shaped and Y-shaped channel are carried out.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.10
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• pp.653-658
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• 2016

A study on the measurement of critical heat flux using the transient inverse heat conduction method in spray cooling was performed. The inverse heat conduction method estimates the surface heat flux or temperature using a measured interior temperature history. The effects of the measuring time interval and location of temperature measurement on the measurement of critical heat flux were primarily investigated. The following results were obtained. The estimated critical heat flux decreased as the time interval of temperature measurement increased. Meanwhile, the effect of measurement location on critical heat flux was not significant. It was also found, from the experimental results, that the critical superheat increased as the measurement location of thermocouple neared the heat transfer surface.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.624-629
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• 2001

An experimental study was performed to investigate adiabatic wall temperature and heat transfer coefficient around on a module with longitudinal fin heat sink cooled by forced air flow. In the first method, inlet air flow(1-7m/s) and input power(3-5W) was varied after a heated module were placed on an adiabatic floor($320{\times}550{\times}1mm^{3}$). An adiabatic wall temperature was determinated to use liquid crystal film(LCF). In the second method to determinate heat transfer coefficient, inlet air flow(1-7m/s) and the heat flux of rubber heater($0.031-0.062\;W/cm^{2}$) was varied after an adiabatic module was placed on rubber heater covering up an adiabatic floor. In addition, surface oil-film visualization were performed to characterize the macroscopic flow-field around a module.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.218-226
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• 1994

Laminar flow and heat transfer in a channel with blockages are obtained numerically in a Reynolds-number range of $100{\leq}Re{\leq}400$. A boundary-fitted curvilinear coordinate system is generated for irregular boundary of the physical region, and solutions of Navier-Stokes equation and energy equation are obtained by finite analytic method in the transformed computational domain. The flow separates in downstream of the blockage and the length of separated-flow region increases with Reynolds number. The heat flux is high on the top of the blockages and increase in the heat transfer occurs where the fluid reattaches the wall. Comparison between computed streamlines and experimental flow-visualization is also presented and discussed.

• Journal of the Korean Society of Visualization
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• v.13 no.3
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• pp.24-28
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• 2015

The temperature of the wafer batch in the furnace was calculated and its visualized temperature field was analyzed. The main heat transfer mechanisms from the heater wall to the wafers were radiation and conduction, and the finite difference method was used to analyze the complex heat transfer including those two mechanisms. The visualized temperature field shows that the direction of the heat flux in the wafer batch varies during the heating process, and the heat in the wafer batch diffuses faster by conduction within the wafer than by radiation between the wafers, in the condition of the constant temperature at the heater wall and cap.

• 한국전산유체공학회:학술대회논문집
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• 1997.10a
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• pp.92-98
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• 1997

A finite-difference method based on characteristic upwind flux difference splitting has been studied on the blowing effect on the wall heat transfer over blunt-bodies. As the blowing rates increased, the wall heat transfer rate decreased and the temperature gradient also decreased compared with no blowing case. The heat trasfer rate at Mach No. 20 was almost twice higher than that of Mach No. 15 at 50km altitude. The surface blowing can be an effective mechanism to reduce the surface heat transfer rate at hypersonic flight condition.