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거친외벽면을 가진 동심환형관내에서 완전히 발달된 유동의 난류구조
안수환,Ahn, S.W. 대한설비공학회 1999 설비공학 논문집 Vol.11 No.1
For roughened annular pipes with diameter ratios of 0.26, 0.39, and 0.56 and with Reynolds numbers ranging 13,000 to 67,000, friction factor, autocorrelation coefficients, power spectral density functions, and integral length scales for each flow condition using X-type hot wire anemometry system are experimentally investigated. Distributions of these quantities show that the times which the streamwise autocorrelation coefficients become zero first increase with decreasing the radius ratios of concentric annuli and Reynolds numbers, however the power spectra density functions increase with increasing the radius ratios and Reynolds number.
내·외벽에 거칠기가 있는 이중동심관 유동에 대한 실험적 연구
안수환,정양범,김경천,Ahn, S.W.,Jung, Y.B.,Kim, K.C. 대한설비공학회 1995 설비공학 논문집 Vol.7 No.1
Fully developed turbulent flow through three concentric annuli with both the rough inner and outer walls was experimentally investigated for a Reynolds number range Re=15,000-85,000. Measurements were made of the pressure drop, the positions of zero shear stress and maximum velocity, and the velocity distributions in annuli of radius ratios, ${\alpha}=0.26$, 0.4 and 0.56, respectively. The experimental results showed that the positions of zero shear streess and maximum velocity were only weakly dependent on the Reynolds number. It was also found that the position of zero shear stress was not coincident with that of maximum velocity. Furthmore, the former was influenced more sensitively than the latter on the square-ribbed roughness along the axial direction.
채널 내에 설치된 2개의 경사진 배플에 의한 열전달 효과에 관한 수치해석
S. W. Ahn(안수환),H. K. Kang(강호근),B. K. P. Ary(아리바시아) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-
Baffles enhance heat transfer by disturbing boundary layer and bulk flow, creating impingement, and increasing heat transfer surface area. This study was performed to determine how the two inclined baffles (α=5°; perforated models) placed at a rectangular channel affect heat transfer and associated friction characteristics. The parametric effects of perforated baffles (3, 6 and 12 holes) and flow Reynolds number ranging from 28,900 to 61,800 on the heated target surface are explored. Comparisons of the experimental data with the numerical results by commercial code CFX 10.0 are presented. As for the investigation of heat transfer behaviors on local Nusselt number with two baffles placed at <SUP>χ</SUP>/Dh =0.8 and <SUP>χ</SUP>/Dh=8.0 of the edge of baffles, it is evident that the inclined perforated baffles augment overall heat transfer significantly by both jet impingement and boundary layer separation. There exists an optimum perforation density to maximize heat transfer coefficients; i.e., the average Nusselt number increases with increasing number of holes, but the friction factor decreases with an increase in the hole number placed at baffles.