• 설비공학논문집
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• 제4권3호
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• pp.155-162
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• 1992

Theoritical Study is performed on heat transfer and fluid flow induced by square-ribbed roughness elements in a concentric annulus. The fluid properties were assumed to be constant, and the radius($r_m$) of the maximum speed point was found by using the principle of equation of Leung and Labib. The Nusselt number and friction factor as a function of the Reynolds number($R_e=10^4$, $5{\times}10^4$, $7{\times}10^4$, $10^5$) in artifical roughness $S/{\epsilon}=5,10,20,30$, $P/{\epsilon}=2,5,8$ and prandtl number = 0.72 have been discussed. In this study, it has been found that the Nusselt number and friction factor of rough wall are larger than those of smooth ones.

• 산업기술연구
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• 제24권A호
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• pp.139-155
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• 2004

A room and pillar mining method has been adopting at the Jeungsun limestone mine. To check stability of pillar with multiple and irregular openings, the size, shape and spacing of rib pillar were first designed using some empirical suggestions. The Finite Difference Method(FDM)was used to analyze the pillar stability. Twelve different cases with the variation of K(horizontal/vertical stress)values, different height and different spacing of pillar were used in this study. Finally Mohr-Coulomb criterion was adopted to calculate the safety factors. Horizontal and vertical displacement, maximum and minimum principal stresses, range of plastic zone and safety factors were calculated at each case. As a result of analysis, the size of one block is 160m long, 70m wide, 40m high with 20m wide rib pillar and 20m square column pillar. The overall recovery at this case can be estimated about 40%.

• 대한기계학회논문집
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• 제18권7호
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• pp.1866-1872
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• 1994

Turbulent flow in a channel with a square rib periodically mounted on one wall is studied by large-eddy simulation(LES). An efficient 3D Navier-Stokes solver has been written for this geometry using a fractional step method and a multi-grid technique. The Reynolds number considered is 82, 000 based on the mean velocity above the obstacle height. Near-wall turbulence is approximated by a wall-layer model based on the turbulence intensity at the grid point nearest a solid wall. The results show a good qualitative agreement with experiments currently available for a single rib, indicating that LES can be a useful tool in simulating complex turbulent flows.

• 동력기계공학회지
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• 제18권2호
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• pp.12-18
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• 2014

The local heat transfer of developed turbulent flows in the stationary ribbed rectangular convergent channels has been investigated experimentally. The rectangular convergent channels with one ribbed surface only have the inclination of $0.72^{\circ}$ and $1.43^{\circ}$ at which the ribbed wall is manufactured with a fixed rib height (e) of 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. The local heat transfer characteristics of the rectangular convergent channels are quite different from those of the ribbed square straight channel.

• 동력기계공학회지
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• 제10권1호
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• pp.25-33
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• 2006

거칠기가 한 벽면과 두 벽면에 설치된 사각채널에서 비압축성 유체유동과 열전달을 조사하기위해 3차원 수치모사를 행하였다. CFX (version 5) software package 를 사용하여 계산하였다. 거친 벽은 $45^{\circ}$경사진 거칠기가 설치되어 있다. 채널의 4 벽면은 일정한 열 유속으로 가열하였다. 수치계산 결과는 실험값과 잘 일치 하였다. 연구의 조건은 거칠기 피치와 높이의 비가 8이고, 거칠기 높이와 채널 수력직경의 비가 0.067이며, 레이놀즈수의 범위는 7,600에서 24,900이었다. 연구의 결과는 열전달계수와 마찰계수는 사각채널에서 거친 벽면의 수가 클수록 증가 함을 보였다.

• 동력기계공학회지
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• 제10권3호
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• pp.17-22
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• 2006

Surface modifications like rib-roughening and displaced insert devices like the twisted tape are commonly used in applications such as compact heat exchangers and cooling systems. In this paper, regionally averaged heat transfer distributions in square channels with twisted tape inserts and with twisted tape inserts plus interrupted ribs are respectively investigated. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. Each wall of the square channel is composed of isolated aluminum sections. Regionally averaged Nusselt number and channel averaged Nusselt number in turbulent air flows are presented for Reynold numbers from 8,900 to 29,000. We have obtained the following conclusions from the experimental study: 1) The local Nusselt number in the two-sided heated case is higher than that in the four-sided heated condition. 2) In the 4 heating wall channel with twisted tape inserts, Nusselt number based on bottom wall temperature is enhanced by 1.2 - 1.6 times if adding the axial interrupted ribs on the bottom wall only. 3) The twisted tape with interrupted ribs under the two-sided heating condition produces the highest heat transfer coefficient.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.117-120
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• 2008

Numerical simulations and experiment of a hydrodynamic and thermally developed turbulent flow through square ducts (3.0 ${\times}$ 3.0 cm) with twisted tape inserts and with twisted tape inserts plus interrupted ribs are conducted to investigate regionally averaged heat transfer and friction factors. Turbulent swirl flows having Reynolds numbers ranging from 8,900 to 29,000, a rib height-to-channel hydraulic diameter(e/D$_h$) of 0.067, and a length-to-hydraulic diameter(L/D$_h$) of 30, are considered. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. The twisted tape has 0.1 mm thick carbon steel sheet with diameter of 2.8 cm, length of 90 cm, and 2.5 turns. Each wall is composed of isolated aluminum sections, and two cases of surface heating are set. The results show that uneven surface heating enhances the heat transfer coefficient over uniform heating conditions, and square ducts with twisted tape inserts plus interrupted ribs produces the best overall transfer performance.

• 동력기계공학회지
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• 제9권1호
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• pp.30-35
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• 2005

Repeated ribs are used on heat exchanger surfaces to promote turbulence and to enhance convective heat transfer. Applications include fuel rods of gas-cooled nuclear reactors, inside cavities of turbine blades, and internal surfaces pipes used in heat exchangers. Despite the great number of literature papers, only few experimental data concerns detailed distributions of friction factors and heat transfer coefficients in square channels varying the number of rough walls. This issue was tackled by investigating effects of different number of ribbed walls on heat transfer and friction characteristics in square channel. The rough wall had a $45^{\circ}$ inclined square rib. Uniform heat flux was maintained on the whole inner heat transfer channel area. The heat transfer coefficient and friction factor values increased with increasing the number of rough walls.

• 대한기계학회논문집B
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• 제29권3호
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• pp.340-348
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• 2005

Repeated ribs are used on heat exchange surfaces to promote turbulence and enhance convective heat transfer. Applications include fuel rods of gas-cooled nuclear reactors, inside cavities of turbine blades, and internal surfaces pipes used in heat exchangers. Despite the great number of literature papers, only few experimental data concern detailed distributions of friction factors and heat transfer coefficients in square channels varying the number of rough walls. This issue is tackled by investigating effects of different number of ribbed walls on heat transfer and friction characteristics in square channel. The rough wall have a $45{\circ}C$ inclined square rib. Uniform heat flux is maintained on whole inner heat transfer channel area. The heat transfer coefficient and friction factor values increase with increasing the number of rough walls.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
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• pp.1083-1090
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• 2005

Repeated ribs are used on heat exchange surfaces to promote turbulence and enhance convective heat transfer. Applications include fuel rods of gas-cooled nuclear reactors, inside cavities of turbine blades, and internal surfaces pipes used in heat exchangers. Despite the great number of literature papers, only few experimental data concern detailed distributions of friction factors and heat transfer coefficients in square channels varying the number of rough walls. This issue is tackled by investigating effects of different number of ribbed walls on heat transfer and friction characteristics in square channel. The rough wall have a 45$^{\circ}$ inclined square rib. Uniform heat flux is maintained on whole inner heat transfer channel area. The heat transfer coefficient and friction factor values increase with increasing the number of rough walls.