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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.
수평형 배관에서 고체입자 농도가 마찰계수에 미치는 효과
안수환(S. W. Ahn),아리바시아 크리시나부트라(A. B. K Putra) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-
Generally, the economic concept of optimized design and operating conditions in fluidized bed heat exchangers can hardly be realized. Because the lack of fundamental knowledge about the particle flows, a fluidized bed heat exchanger is rather limited. In the present work, measurements are made on pressure drops and friction factors in the horizontal circular tube with solid particles in the circulating water. Two different solid particles of diameters of 3㎜ and 4㎜ are covered. The Reynolds numbers are ranged from 10,000 to 45,000. It is concluded that the friction factors for the particles of 4㎜ diameter are much higher than those for the particles of 3㎜ diameter. And at the lower particle concentration, the friction factors are strongly influenced by the fluid velocity rather than the particle concentration; However, the effect of the particle concentration on friction factors is also significantly higher at a higher particle concentration operating condition.