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차단구조가 적용된 파형 배열충돌제트의 유동 및 열전달 특성
조형희,배성호,김선호,손호성,김태현 대한기계학회 2023 大韓機械學會論文集B Vol.47 No.5
Impingement jet cooling is a method to obtain high heat transfer performance by injecting coolant on the target surface. A cooling method that secures high heat transfer performance over a large area by arranging multiple impingement jets is called an array impingement jet. However, since the coolant injected from the holes arranged in a certain direction impinge with the target surface and exit through the outlet formed downstream, a cross-flow is generated, which results in a degradation of cooling performance. Recently, corrugated structures have been studied to overcome the degradation of heat transfer performance due to cross-flow. In this study, a block-off structure was applied to the corrugated structure for more effective cross-flow reduction. The block-off structure serves to minimize the degradation of heat transfer performance due to cross-flow by forcibly moving coolant to the corrugated structure. The numerical analysis was performed to investigate the flow and heat transfer characteristics of the array impingement jet with the corrugated structure and block-off structure. With the block-off structure, it was confirmed that the thermal performance was improved by about 5% compared to the existing geometry. 충돌제트 냉각은 냉각 대상면에 제트 형태의 냉각 유체를 분사하여 국소적으로 높은 열전달 성능을 얻는 냉각 방식이다. 이러한 충돌제트를 다수 배열하여 넓은 면적에서 높은 열전달 성능을 확보하는 냉각 방식을 배열충돌제트라 한다. 하지만 일정한 방향으로 배열된 충돌제트에서 분사된 냉각 유체들은 냉각 대상면에 충돌 후 하류에 형성되어 있는 출구로 빠져나가려 하기 때문에 횡방향 유동이 생성되고 이는 하류에서 냉각성능이 저하되는 결과를 가져온다. 이를 개선하기 위해 최근 횡방향 유동이 이동할 수 있는 공간을 확보한 파형 배열충돌제트가 연구되고 있다. 본 연구에서는 더욱 효과적인 횡방향 유동의 감소를 위하여 파형 배열충돌제트에 차단 구조를 적용하였고, 이는 냉각 유체가 냉각 대상면에 충격 후 파형구조로 강제로 이동하게 함으로써 횡방향 유동으로 인한 열전달 감소현상을 최소화시키고자 하였다. 수치해석을 통해 차단구조가 적용된 파형 배열충돌제트 형상에 따른 열전달 및 유동 특성을 분석하였고, 차단구조가 설치된 결과에서 기존대비 약 5%가 향상된 열효율이 나타나는 것을 확인하였다.
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.