Seung-Hwan Yu

Thermal Analysis of a Radial Heat Sink with Radiation and Natural Convection

A radial heat sink, adopted to LED(light emitting diode) downlight, was optimized. Discrete transfer radiation model (DTRM) was used to calculate radiation heat transfer, and numerical model was verified with experimental results. The effects of number of fin, long fin length and middle fin length on overall thermal resistance and radiation heat transfer were analyzed. As the emissivity increased, thermal resistance decreased due to the increment of radiation heat transfer. The radial heat sink was optimized and optimum number of long fins is 19~28, optimum length of long fin is about half of radius of heat fink and optimum fin ratio is 0.4~0.7.본 연구는 LED 조명기구에 적합한 원형 히트싱크의 최적설계를 수행하였다. DTRM 복사 모델을 이용하여 자연대류와 복사 열전달을 수치적으로 해석하였고, 수치모델을 실험을 통하여 검증하였다. 휜 개수, 긴 휜 길이, 중간 휜 길이가 전체 열저항 및 복사 열전달에 미치는 영향을 조사하였고, 그 결과 방사율이 증가할수록...

Analysis of Film Flow Around Rotating Roller Partially Immersed in Ink

This study is intended to analyze the effect of thin ink-film thickness around rotating printing roll on the printing quality in the gravure printing process which is used for making electronics circuit like a RFID tag with a conductive ink. The present work numerically estimates the film thickness around rotating roller partially immersed in ink for which the volume of fluid (VOF) method was adopted to figure out the film formation process around rotating roller. Parameter studies were performed to compare the effect of ink properties (viscosity, surface tension), operating condition (roller rotating speed, initial immersed angle) on the film thickness. The result indicates that the film thickness has a strong dependency on the rotating speed, while the surface tension has negligible effect.

The analysis of film flow around rotating roller partially immersed ink

This study is intended to analyze the effect of thin ink-film thickness around rotating printing roll on the printing quality in the gravure printing process which is used for making electronics circuit like a RFID tag with a conductive ink. The present work numerically estimates the film thickness around rotating roller partially immersed in ink, in which the volume of fluid (VOF) method was adopted to figure out the film formation process around rotating roller. Parameter studies were performed to compare the effect of ink viscosity, surface tension, roller rotating speed and immersed angle on the film thickness. The result indicates that the film thickness has a strong dependency on the fluid viscosity, while the surface tension effect becomes negligible.

Multi-objective optimization of a radial heat sink considering radiation effect

A radial heat sink was investigated, considering both natural convection and radiation. Experiments were performed to validate numerical results and a close agreement was found. The effect of radiation on total heat transfer was examined by varying emissivity, and it was found that the maximum radiation contribution was 27%. The radial heat sink was optimized to maximize thermal performance. The thermal performance was enhanced by 12.3% while the mass increased by 20%. Radiation (emissivity) had a significant effect on the optimum long fin length when only thermal performance was considered. The average thermal resistance decreased by 8.7% for the optimized model with the same mass as the reference model, and the effect of radiation on total heat transfer was greater than the effect of natural convection.