• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.241-247
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• 2001

A comparison of fully developed heat transfer and friction factor characteristics has been made in rectangular ducts with ones roughened by five different shapes. The effects of rib shape geometries and Reynolds number are examined. The rib height-to-duct hydraulic diameter, pitch-to-height ratio, and aspect ratio of channel width to height are fixed at e/De=0.0476, P/e=8, and W/H=2.33, respectively. To understand the mechanisms of the heat transfer enhancements, the measurements of the friction factors are also conducted in the smooth and rough channels. The data indicates that the triangular type rib has a substantially higher heat transfer performance than any other ones in the range we studied.

• 대한기계학회논문집B
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• 제27권9호
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• pp.1351-1359
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• 2003

This study presents a numerical procedure to optimize shape of streamwise periodic ribs mounted on both of the principal walls to enhance turbulent heat transfer in a rectangular channel flow. The response surface method is used as an optimization technique. The optimization is based on Navier-Stokes analysis of flow and heat transfer with $k-{\varepsilon}$ turbulence model. The width-to-height ratio of a rib, rib height-to-channel height ratio and rib pitch to rib height ratio are chosen as design variables. The object function is defined as a function of heat transfer coefficient and friction drag coefficient with weighting factor. Optimum shapes of the rib have been obtained for the range of 0.02 to 0.1 of weighting factor.

• 설비공학논문집
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• 제13권5호
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• pp.341-347
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• 2001

A comparison of fully developed heat transfer and friction factor characteristics has been made in rectangular ducts with ones roughened by five different shapes. The effects of rib shape geometries and Reynolds number are examined. The rib height-to-duct hydraulic diameter, pitch-to height ratio, and aspect ratio of channel width to height are fixed at $e$/De=0.0476, P/$e$=8, and W/H=2.33, respectively. To understand the mechanisms of the heat transfer enhancements, the measurements of the friction factors are also conducted in the smooth and rough channels. The data indicates that the triangular type rib has a substantially higher heat transfer performance than any other ones in the range we studied.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.627-630
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• 2003

This work presents a numerical procedure to optimize the shape of three-dimensional channel with angled ribs mounted on one of the walls to enhance turbulent heat transfer. The response surface method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of flow and heat transfer. SST turbulence model is used as a turbulence closure. The width-to-height ratio of the rib, rib height-to-channel height ratio, pitch-to-rib height ratio and attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related terms with weighting factor. D-optimal experimental design method is used to determine the data points. Optimum shapes of the channel have been obtained for the weighting factors in the range from 0.0 to 1.0.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.782-789
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• 2001

Local heat/mass transfer and friction loss in a square duct roughened with various types of continuous and discrete rib turbulators are investigated. The combined effects of the gap flows of the discrete ribs and the secondary flows are examined for the purpose of the reduction of thermally weak regions and the promotion of the uniformity of heat/mass transfer distributions as well as the augmentation of average heat/mass transfer. The rib-to-rib pitch to the rib height ratio (p/e) of 8 and the rib angles of 90 and 60 deg are selected with $e/D_{h}=0.08$. The vortical structure of the secondary flows induced by the parallel angled arrays are quite distinct from that induced by the cross angled arrays. This distinction influences on heat/mass transfer and friction loss in all the tested cases. The gap flows of the discrete ribs reduce the strength of the secondary flows but promote local turbulence and flow mixing. As a result, the fairly uniform heat/mass transfer distributions are obtained with two row gaps.

• 동력기계공학회지
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• 제16권6호
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• pp.30-37
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• 2012

Effect of rib heights is found as significant parameter to enhance convective heat transfer performance under laminar and low turbulent regime. Circular ribs with different ribheight to channel height ratios, e/H = 0.05, 0.1, 0.15, are fabricated over the copper substrate respectively in a rectangular duct having 7.5 cross sectional aspect ratio. Only one rib pitch to rib height ratio (P/e = 10) has been chosen for all different height ribs. The result shows that the arithmetic average of turbulence intensity decreases with decreasing roughness height calculated between two ribs under laminar and low turbulent region. It occurs because the area of recirculation and reattachment zone also decreases with decreasing rib height. Optimum thermal enhancement factor is derived by 0.1 rib height to channel height ratio under low turbulent region but 0.15 rib height to channel height ratio gives maximum subjected to laminar flow.

• 대한기계학회논문집B
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• 제22권4호
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• pp.530-541
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• 1998

Heat transfer augmentation in a rib-roughened duct is affected by the rib configurations, such as rib height, angle of attack, shape, rib to rib pitch, and aspect ratio of a duct. These have been the main subjects in studying the average heat transfer and the friction loss of the fully developed flow. Investigating distributions of local heat transfer coefficients and flow patterns in a duct with the rib turbulators is necessary to find the characteristics of heat transfer augmentation and to decide the optimal configurations of ribs. In the present study the numerical analyses and the mass transfer experiments are performed to understand the flow through a rib roughened duct and the heat transfer characteristics with various angles of attack of ribs. A pair of counter-rotating secondary flow in a duct has a main effect on the lateral distributions of local mass transfer coefficients. Downwash of the rotating secondary flow, reattachment of main flow between ribs and the vortices near ribs and wall enhanced the mass transfer locally up to 8 times of that in case of the duct without ribs.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.178-184
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• 2005

The present study investigates the effects of bleed flow on heat/mass transfer and pressure drop in a rotating channel with transverse rib turbulators. The hydraulic diameter ($D_h$) of the square channel is 40.0 mm. The bleed holes are located between the rib turburators on leading surface and the hole diameter (d) is 4.5 mm. The square rib turbulators are installed on both leading and trailing surfaces. The rib-to-rib pitch is 10.0 times of the rib height (e) and the rib height-to-hydraulic diameter ratio ($e/D_h$) is 0.055. The tests were conducted at various rotation numbers (0, 0.2, 0.4), while the Reynolds number and the rate of bleed flow to main flow were fixed at 10,000 and 10%, respectively. The results suggest that the heat/mass transfer characteristics in the internal cooling passage are influenced by rib turbulators, bleed flow and the Cariolis force induced by rotation. For the rotating ribbed passage with bleed flow, the heat/mass transfer on the leading surface is hardly affected by bleed flow, but that on the trailing surface decreases due to the diminution of main flow. The results also show that the friction factor decreases with the bleed flow.

• 대한기계학회논문집B
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• 제25권11호
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• pp.1640-1649
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• 2001

The present study investigates the effects of various rib arrangements on heat/mass transfer in the cooling passage of gas turbine blades. A complex flow structure occurs in the cooling passage with rib turbulators which promote heat transfer on the wall. It is important to increase not only the heat transfer rates but also the uniformity of heat transfer in the cooling passage. A numerical computation is performed using a commercial code to calculate the flow structures and experiments are conducted to measure heat/mass transfer coefficients using a naphthalene sublimation technique. A square channel (50 mm $\times$ 50 mm) with rectangular ribs (4 mm $\times$ 5 mm) is used fur the stationary duct test. The experiments focus on the effects of rib arrangements and gap positions in the discrete ribs on the heat/mass transfer on the duct wall. The rib angle of attack is 60°and the rib-to-rib pitch is 32 mm, that is 8 times of the rib height. With the inclined rib angle of attack (60°), the parallel rib arrangements make a pair of counter rotating secondary flows in the cross section, but the cross rib arrangements make a single large secondary flow including a small secondary vortex. These secondary flow patterns affect significantly the heat/mass transfer on the ribbed wall. The heat/mass transfer in the parallel arrangements is 1.5 ∼2 times higher than that in the cross arrangements. However, the shifted rib arrangements change little the heat/mass transfer from the inline rib arrangements. The gap position in the discrete rib affects significantly the heat/mass transfer because a strong flow acceleration occurs locally through the gap.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2211-2218
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• 2003

The present study investigates heat/mass transfer characteristics in a rotating two-pass duct for smooth and ribbed surfaces. The duct has an aspect ratio of 0.5 and a hydraulic diameter of 26.67 mm. 70-angled rib turbulators are attached on the leading and trailing sides of the duct in parallel and cross arrangements. The pitch-to-rib height ratio is 7.5 and the rib height-to-hydraulic diameter ratio is 0.075. The Reynolds number based on the hydraulic diameter is constant at 10,000 and the rotation number ranges from 0.0 to 0.2 Detailed local heat/mass transfer coefficients are measured using a naphthalene sublimation technique. The results show that the secondary flows generated by the $180^{\circ}-turn$, rib turbulators, and duct rotation affect the wall heat/mass transfer distribution significantly, As the duct rotates, the rotaion-induced Coriolis force deflects the main flow and results in differences on the heat/mass transfer distribution between the leading and trailing surfaces. Its effects become more dominant as the rotaion number increases. Discussions are presented describing how the rib configuration and the rotaion speed affect the flow patterns and local heat/mass transfer in the duct.