• Journal of the Korean Society of Propulsion Engineers
• /
• v.11 no.5
• /
• pp.14-22
• /
• 2007

A reversed trapezoidal fin with variable lateral surface slope is optimized using a two-dimensional analytic method. For a fin base boundary condition, convection from the inside fluid to the inside wall and conduction from the inside wall to the fin base are considered. Heat loss from the fin tip surface is not ignored. The maximum heat loss at the practical fin length, the corresponding optimum fin efficiency, fin length and fin base height are presented as a function of the fin inside and outside convection characteristic numbers. One of the results shows that the optimum fin shape becomes 'fatter and shorter' as the ratio of fin tip height to base height increases.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.17 no.6
• /
• pp.117-123
• /
• 2018

Automotive headlamps have been continuously developed as one of the most important devices for securing the driver's view, and the LED lamps are getting popular in recent years. However, in case of the LED lamps, because the heat generated by the LED lamps are too high, it shorten the product life and lower the LED efficiency. Therefore, this study was investigated the cooling characteristics of the LED lamp heat sink for automobile by forced convection for LED heat generation control. In order to analyze the cooling characteristics of the heat sink, the temperature distribution results were investigated through the experiment and computational analysis under the increase of the air flow velocity, and the convective heat transfer coefficient was obtained. Also, convective heat transfer coefficient was calculated by the theoretical formula under the same condition and compared with experimental and computational results. From the result of this study, as the air flow velocity around the heat sink fins increased, the convective heat transfer coefficient significantly increased, confirming the improvement in the cooling effect.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1996.06a
• /
• pp.522-522
• /
• 1996

An investigation of the effects of transverse magnetic field and Peltier effect on melt convection and macrosegregation in vertical Bridgman crystal grosth of Te doped InSb was been carried out by means of microstructure observation, Hall measurement, electrical resistivity measurement and X-ray analysis. Before the experiments, Interface stability, convective instability and suppression of convection by magnetic field were calculated theoretically. After doping 1018, 1019 cm-3 Te in InSb, the temperature of Bridgman furnace was set up at $650^{\circ}C$. The samples were grown in I.D. 11mm, 100mm high quartz tube. The velocity of growth was about 2${\mu}{\textrm}{m}$/sec. In order to obtain the suppression of convection by magnetic field in the middle of growth, 2-4KG magnetic field was set on the melt. For searching of the shape of solid-liquid interface and the actual velocity of crystal growth, let 2A current flow from solid to liquid for 1second every 50seconds repeatedly (Peltier effect). The grown InSb was polycrystal, and each grain was very sharp. There was no much difference between the sample with and without magnetic field at a point of view of microstructure. For the sample with Peltier effect, the Peltier marks(striation) were observed regularly as expected. Through these marks, it was found that the solid-liquid interface was flat and the actual growth velocity was about 1-2${\mu}{\textrm}{m}$/sec. On the ground of theoretical calculation, there is thermosolutal convection in the Te doped InSb melt without magnetic field in this growth condition. and if there is more than 1KG magnetic field, the convection is suppressed. Through this experiments, the effective distribution coefficients, koff, were 0.35 in the case of no magnetic field, and 0.45 when the magnetic field is 2KG, 0.7 at 4KG. It was found that the more magnetic field was applied, the more convection was suppressed. But there was some difference between the theoretical calculation and the experiment, the cause of the difference was thought due to the use of some approximated values in theoretical calculation. In addition to these results, the sample with Peltier effect showed unexpected result about the Te distribution in InSb. It looked like no convection and no macrosegregation. It was thought that the unexpected behavior was due to Peltier mark. that is, when the strong current flew the growing sample, the mark was formed by catching Te. As a result of the phenomena, the more Te containing thin layer was made. The layer ruled the Hall measurement. The values of resistivity and mobility of these samples were just a little than those of other reference. It was thought that the reason of this result was that these samples were due to polycrystal, that is, grain boundaries had an influence on this result.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.21 no.5
• /
• pp.29-36
• /
• 2017

In this study, a numerical analysis is made of the fluid flow and heat transfer characteristics in the solar arrays of HALE (High Altitude Lond Endurance) UAV. In the stratosphere where UAV operates, high level solar radiation is induced, heat transfer decreases due to natural convection and forced convection is dominated by ambient flow. In order to predict the solar array temperature range in this environment condition, the conjugate heat transfer analysis was carried out for the solar arrays on the main wing. The investigation focused on the temperature distribution of solar array and heat transfer characteristics according to influence of solar energy, flight condition as vehicle speed, air density, temperature.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.15 no.3
• /
• pp.239-249
• /
• 2005

Ventilation effect is analyzed for boiler building with multiple heat sources. Air flow inside the boiler building is characterized as turbulent mixed convection. Analysis methodology is set up with two different $k-{\varepsilon}$ type models (standard $k-{\varepsilon}$, RNG $k-{\varepsilon}$). Two different cases with high and low outside temperature are analyzed. In case of high outside temperature condition, mixed convection is well realized inside the boiler building. With different upper louver opening rate, air flow is also well established and proper opening rate is found to meet design limit in case of low outside temperature condition. Difference of analysis results for two different turbulence models are not significant. Therefore, analysis methodology with simple $k-{\varepsilon}$ turbulence model is found to be reliable for the boiler building ventilation analysis. However, more simplified geometrical model is desired to expand its application.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.5
• /
• pp.979-990
• /
• 1989

Natural convection heat transfer has been investigated numerically in the vertical annulus filled withsaturated porous material for the aspect ratio less than unity. The inner wall of the annulus is exposed to constant heat flux condition and the outer wall is cooled to keep isothermal condition. The upper and the lower horizontal wall are assumed to be insulated. Under conditions ranging 50 .leq. Ra .leq. 10000, 1 .leq. RD .leq. 12, the characteristics of flow and heat transfer have been investigated. The results show that average Nusselt numbers increase when the radius ratio increases and the multicellular flows are not detected under the present conditions. Isothermal lines are plotted within the porous media. Temperatures of the inner wall with constant heat flux conditions and the local heat flux rate of the cooled outer wall with constant temperature are also obtained.

• Design & Manufacturing
• /
• v.16 no.2
• /
• pp.46-52
• /
• 2022

As the consumer market in the eco-friendly vehicle industry grows, the demand for water pump in a electric car parts market. This study intend to propose a mathematical model that can verify the effect of improving thermal properties when a non-conductive cooling filler liquid is introduced into an electric vehicle water pump. Also, the pros and cons of the immersion cooling method and future development way were suggested by analyzing the cooling characteristics using on the derived analysis solution. Thermal characteristics analysis of electric water pump applied with non-conductive filler liquid was carried out, and the diffusion boundary condition in the motor body and the boundary condition the inside pump were expressed as a geometric model. As a result of analyzing the temperature change for the heat source of the natural convection method and the heat conduction method, the natural convection method has difficulty in dissipating heat because no decrease in temperature due to heat release was found even after 300 sec. Also, it can be seen that the heat dissipation effect was obtained even though the non-conductive filling liquid was applied at the 120 sec and 180 sec in the heat conduction method. It has proposed to minimize thermal embrittlement and lower motor torque by injecting a non-conductive filler liquid into the motor body and designing a partition wall thickness of 2.5 mm or less.

• Journal of Industrial Technology
• /
• v.31 no.A
• /
• pp.21-25
• /
• 2011

A comparison of temperature distributions along the fin length coordinate between two different fin tip boundary conditions for a circular pin fin is made by using the one-dimensional analytic method. One tip boundary condition is the actual fin tip boundary condition and fin tip temperature is arbitrarily given for another fin tip boundary condition. The value of the fin base temperature is depend on the fin base thickness and fin radius. One of the results shows that the temperature distribution along the fin length coordinate for the actual fin tip boundary condition and that for the arbitrarily given fin tip temperature are the same if the arbitrarily given fin tip temperature and the fin tip temperature for the actual fin tip boundary condition are the same.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.2
• /
• pp.169-176
• /
• 2000

Natural convection in a wide-gap horizontal annulus is considered, and the transition of flows and the bifurcation phenomenon are investigated for the fluids with Pr=0.2 and 0.3. At Pr=0.2, a bicellular flow pattern is observed at high Rayleigh number, and the solution is unique. At Pr=0.3, both the steady unicellular and bicellular flows exist above a certain critical Rayleigh number. For the fluids of Pr=0.2, the bicellular flow can be obtained by the impulsive heating of the inner cylinder, but it is not obtained from the zero initial condition for Pr=0.3. Hysteresis phenomena have not been observed. A transition from a bicellular flow to a unicellular flow occurs for Pr=0.3.

• 한국전산유체공학회:학술대회논문집
• /
• 2009.04a
• /
• pp.355-362
• /
• 2009

Most material of engineering interest undergoes solidification process from liquid to solid state. Identifying the underlying mechanism during solidification process is essential to determine the microstructure of material which governs the physical properties of final product. In this paper, we expand our previous two-dimensional numerical technique to three-dimensional simulation for computing dendritic solidification process with fluid convection. We used Level Contour Reconstruction Method to track the moving liquid-solid interface and Sharp Interface Technique to correctly implement phase changing boundary condition. Three-dimensional results showed clear difference compared to two-dimensional simulation on tip growth rate and velocity.