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딤플을 적용한 열교환기 표면에서 반대편 돌기 형상으로 인한 국소 열/물질전달 및 열성능 특성
권현구(Hyun Goo Kwon),조형희(Hyung Hee Cho) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
In this study, we have investigated the effects of opposite protrusion wall on the local heat/mass transfer characteristics and thermal performances of dimpled channel. A mass transfer experiment using naphthalene sublimation technique was used. The dimple print diameter and the dimple depth were fixed at 20㎜ and 4㎜, respectively. The Reynolds numbers based on the channel height were 1000, 3000 and 5000 in this study. High heat/mass transfer coefficients were occurred around rear rim of the dimple and rear plateau region by the main flow impinging and edge vortices from the dimple edge, respectively. The Opposite protrusion wall highly augmented the heat/mass transfer coefficient around the rear rim of the dimple. In-lined arrangement of the dimples and the protrusions showed the highest value of the performance factor.
2차 유동 영역에서 꺽임각 변화에 따른 주름진 사각 덕트에서의 열/물질전달 및 유동 특성
권현구(Hyun Goo Kwon),황상동(Sang Dong Hwang),조형희(Hyung Hee Cho) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
The present study investigates the two dimensional flow and heat/mass transfer characteristics of wavy duct with various corrugation angles. For the heat/mass transfer coefficients, a naphthalene sublimation technique is used. Numerical analysis and wall pressure measurement show detailed two dimensional flow features. The corrugation angles change from 145° to 100°. The operating Reynolds numbers based on the duct hydraulic diameter vary from 700 to 3,000. The duct aspect ratio maintains 7.3. On the pressure wall, strong flow mixing enhances heat/mass transfer coefficients at the front position. In addition, the rear side of pressure wall, the near of peak, is affected by the acceleration and the shedding of main flow. On the suction wall, however, flow separation and reattachment lead to the valley and the peak of heat/mass transfer coefficient. Also, highly increasing boundary layer at the suction wall affects the decrease of heat/masst transfer. As decreasing corrugation angles, the spanwise average Sherwood number increases and the peak or the valley positions of the local Sherwood number are varied.
낮은 레이놀즈 수 영역에서 단일 딤플에 의한 국소 열/물질전달계수 측정
권현구(Hyun Goo Kwon),황상동(Sang Dong Hwang),조형희(Hyung Hee Cho) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
The objective of this study is to investigate local characteristics of heat/mass transfer coefficients on unit dimple with a low Reynolds number range. Local heat/mass transfer coefficients were presented using naphthalene sublimation method. This paper showed detail descriptions about a 3-D shaped naphthalene casting system. The dimple diamter of this experiment 20 ㎜ and 4 ㎜ in depth. The test duct was 10 ㎜ in height and 200 mm wide. The Reynolds number, based on the duct height was varied from 500 to 5,000. The local heat/mass transfer coefficients showed different characteristics in laminar flow and in turbulent flow, respectively. In laminar flow, averaged heat/mass transfer enhancement level reached up to 2.8. In turbulent flow with low velocity, the enhancement level was 2.1-2.6.
델타윙에 의한 이차유동이 딤플의 열/물질전달 특성에 미치는 영향에 대한 연구
권현구(Hyun Goo Kwon),황상동(Sang Dong Hwang),조형희(Hyung Hee Cho) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
In this study, we have investigated the effects of upstream rectangular winglet pair (RWP) on the heat/mass transfer coefficients in a dimple. Dimple print diameter was fixed at 20mm and the dimple depth was 4.0mm (0.4H). The dimple surface was coated with naphthalene for mass transfer experiment and the test plate was positioned at a rectangular straight duct whose aspect ratio (W/H) was 20. A rectangular winglet pair was positioned at y/d=-2.5. The RWP angle (β) was varied from 15° to 60°. The Reynolds number, based on the duct height (H), was 5,000. with changing the RWP angle (β), the induced vortices had different flow characteristics; longitudinal or transversal vortices. These variation of induced vortices affected on the heat/mass transfer characteristics in the dimple.
주름진 덕트에서 딤플/돌출 형상이 열전달계수에 미치는 영향
권현구(Hyun Goo Kwon),황상동(Sang Dong Hwang),조형희(Hyung Hee Cho) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
Heat transfer and performance characteristics have been investigated for a rectangular wavy duct with dimple or protrusion arrays. The test duct was 15㎜ in height and 105㎜ wide. The print diameter of the dimple/protrusion wall was 12.99㎜ and the depth/height of the dimple/protrusion was 3.75㎜. Local heat transfer coefficients on the dimple/protrusion wall were measured using a transient TLC technique. The Reynolds number was varied from 3,000 to 10,000. For the wavy duct tested in this study, adverse static pressure characteristics occurred at turning region of the wavy duct due to secondary flows. For the wavy duct with protrusion array, higher heat transfer enhancement level of 7.4 times than smooth straight case in maximum was obtained at low Reynolds number due to the high heat transfer enhancement by vortex flows. Also, the protrusion array increased the performance level of 3.0 at low Reynolds number of 3,000.
정원중,권현구,조형희,Jeong, Won-Jung,Kwon, Hyun-Goo,Cho, Hyung-Hee 한국반도체디스플레이기술학회 2006 반도체디스플레이기술학회지 Vol.5 No.3
Because of new requirements related to the employment of SMT(Surface Mounting Technology) manufacturing and the diversity of components on high density PCB(Printed Circuit Boards), Thermal control of the reflow process is required in order to achieve acceptable yields and reliability of SMT assemblies. Accurate control of the temperature distribution during the reflow process is one of the major requirements, especially in lead-free assembly. This study has been performed for reflow process using the commercial CFD(Computational Fluid Dynamics) tool for predicting flow and temperature distributions. Porous plate was installed to prevent leakage flow which was one of the major problem of temperature uniformity in the reflow process. There is a separation region where the flow is turned. Outside wall made of porous plate is to prevent and minimize separation region for acquiring uniform temperature during operation. This paper provided design concept from CFD results of the steady state temperature distribution and flow field inside a reflow oven.
정원중(Won-Jung Jeong),권현구(Hyun-Goo Kwon),조형희(Hyung-Hee Cho) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
Because of new requirements related to the employment of SMT(Surface Mounting Technology) manufacturing and the diversity of components on high density PCB(printed circuit boards), Thermal control of the reflow process is required in oder to achieve acceptable yields and reliability of SMT assemblies. Accurate control of the temperature distribution during the reflow process is one of the major requirements, especially in lead-free assembly. This study has been performed for reflow process using the commercial CFD tool(Fluent) for predicting flow and temperature distributions. There was flow recirculation region that had a weak point in the temperature uniformity. Porous plate was installed to prevent and minimize flow recirculation region for acquiring uniform temperature in oven. This paper provided design concept from CFD results of the steady state temperature distribution and flow field inside a reflow oven.