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짧은 못형핀의 형상 변화에 따른 열전달 및 마찰손실 특성
조형희,Cho, H.H.,Goldstein, R.J. 대한설비공학회 1997 설비공학 논문집 Vol.9 No.3
Average heat transfer coefficients and friction coefficients have been measured from staggered short pin-fin arrays to investigate the effect of fin shapes. Flow entering into the test section is a fully developed duct flow and the Reynolds number ranges from 5,000 to 25,000 based on fin diameter and average approaching velocity. The fin has three different shapes; uniform-diameter circular fin, two stepped-diameter circular fins. Average heat transfer rates change slightly with the fin shapes. However, friction loss(pressure loss) for the stepped-diameter fins is significantly less than that for the uniform-diameter fin. This results indicate that the stepped-diameter fin arrays in duct flow enhance heat transfer rates largely based on unit pumping power.
분체 이송관내 압력 조절을 위한 오리피스 주위에서의 입자 유동 및 마모 해석
조형희,이재근,박호동,서태원,Cho, Hyung-Hee,Lee, Jae-Keun,Park, Ho-Dong,Seo, Tae-Won 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.11
A numerical study is performed to investigate pressure drops, particle trajectories and erosion around orifice plates in pulverized coal pipe lines. Particle impaction rates change significantly with orifice shapes and Stokes numbers. At Reynolds number of $5{\times}10^5$, the pulverized coal flows well with streamlines and do not collide at the orifice plates at small sizes (${\sim}20{\mu}m$). However, the large particles (over $70{\mu}m$) impact on the front face of the orifice and erode the orifice surface. The pressure loss coefficients around the erode orifice are largely different from the designed original orifice.
방사선사진용 디지털 영상시스템의 정량적 평가에 관한 실험적 연구
조형희,김은경,Cho Heang-Hee,Kim Eun-Kyung 대한영상치의학회 1994 Imaging Science in Dentistry Vol.24 No.1
A digital imaging system using Machintosh Ⅱ ci computer, high resolution Sony XC-77 CCD camera, Quickcapture Frame Grabber Board was evaluated for quantitative analysis of standardized periapical film with aluminum step wedge. The results were as follows: 1. Correlation between Al thickness and gray level was high-positively associated(r²=0.99, p<0.001). 2. Correlation between measured weight of experimental lesion and estimated relative lesion volume by digital subtracted radiography was also high-positively associated (r²=0.98, p<0.001). 3. As exposure time was increased, mean gray level was decreased(p<0.01) and slope of regression line between Al thickness and gray level was also decreased (p<0.01). And when the exposure time was shorter than 0.2 second, the value of r² was relatively low. On the basis of the above results, it is considered that this digital imaging system using a Macintosh Ⅱ ci computer & a high resolution CCD monochrome camera will be useful in evaluating digitized image from standardized periapical film quantitatively.
조형희(Hyung-Hee Cho),최항철(Hang-Cheol Choi),김광호(Kwang-Ho Kim),정진택(Jin Taek Chung) 한국유체기계학회 2004 유체기계 연구개발 발표회 논문집 Vol.- No.-
2-dimensional impeller's distinctive feature is expected to have an influence on performance and flow characteristics of centrifugal compressor. And new design method is required for 2-dimensional impeller, because the unique geometry cannot be designed using conventional theories. The objective of this study is to advance new design technology for 2-dimensional impeller and to investigate the performance characteristics of designed 2-dimensional centrifugal compressor. The performance test for 2-dimensional impeller is conducted at 35000, 4000 and 45000rpm. Also numerical calculation is applied by using commercial CFD code, FLUENT, and the results are compared with experimental results.
조형희(Hyung Hee Cho) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
This paper presents the curriculum of creative design and experimental education of School of Mechanical Engineering in Yonsei University. The experimental education has been changed to increase an interest of students and to adjust the needs by industries. New classes of Creative design project(1),(2),(3) have been developed to increase student’s creativity, synthesis ability, design skills, teamwork, and leadership in mechanical engineering.
가스터빈 블레이드 내부 냉각유로에서 단락요철 설치에 따른 열/물질전달 특성 연구
조형희(Hyung Hee Cho),김경민(Kyung Min Kim),김상인(Sang In Kim),이동호(Dong Ho Rhee) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
The present study has been conducted to investigate the effect of discrete ribs and rotation on heat/mass transfer characteristics in a two-pass square duct with 90°-rib turbulators. The rib turbulator has a square cross section of 1.5 ㎜. The rib height-to-hydraulic diameter ratio (e/D<SUB>h</SUB>) is 0.056, and the rib pitch-to-rib height ratio (p/e) is 10. The gap width is the same as the rib height. The rotation number ranges from 0.0 to 0.2 while Reynolds number is fixed to 10,000. In a stationary duct, the heat/mass transfer on the surfaces with discrete ribs is enhanced because the gap flow promotes local turbulence and flow mixing near the ribbed surface. In a rotating duct, the gap flow affects differently the heat/mass transfer on leading and trailing surfaces with discrete ribs. On the leading surface of the first pass, heat/mass transfer is increased due to the gap flow. On the trailing surface of the first pass, however, heat/mass transfer is decreased because the gap flow disturbs reattachment of main flow. The phenomenon is distinctly presented by rotation.