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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.
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.
Heat transfer and friction factor in the ribbed rectangular divergent channel
M. S. Lee(이명성),H. B. Kim(김현범),S. H. Lee(이승호),S. W. Ahn(안수환) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5
The heat transfer and friction factors of developed turbulent flows in the stationary ribbed rectangular divergent channels have been investigated experimentally. The rectangular divergent channels with one sided ribbed surface only have the inclination angles of 0.72° and 1.43° at which the ribbed wall is manufactured with a fixed rib height (e) =10 mm and the ratio of rib spacing (p) to height(e) = 10. The measurement was conducted within the range of Reynolds numbers from 15,000 to 89,000. Because of the streamwise flow deceleration, the heat transfer characteristics of the rectangular divergent channels are quit different from those of the square straight channel. Thermal performances of the ribbed rectangular divergent channels are compared with the fibbed square straight channel under three constraints: identical mass flow rate, identical pumping power, and identical pressure drop. The comparison shows that among the two channels (D<SUB>ho</SUB>/D<SUB>hi</SUB> = 1.16 and 1.49) the divergent channel of D<SUB>ho</SUB>/D<SUB>hi</SUB> =1.49 has the higher thermal performance at the identical mass flow rate, and the divergent channel of Dho/Dhi ?1.16 has the higher thermal performance at the identical pumping power and static pressure drop.