• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.459-466
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• 2005

The present study investigates the heat transfer characteristics of a triangular channel. Three different rib configurations are tested. The ribs are installed on two sides of the channel. The rib height (e) to channel hydraulic diameter is 0.079 and the rib-to-rib pitch (p) is 8 times of the rib height. The rotation number ranges from 0.0 to 0.1 while the Reynolds number is fixed at 10,000. The copper blocks with heaters are installed on the channel walls to measure the regionally averaged heat transfer coefficients. For the stationary $45^{\circ}$ and $135^{\circ}$ ribbed channels, a pair of counter rotating vortices is induced by the angled rib arrangements, and high heat transfer coefficients are obtained on the regions near the inner wall for the $45^{\circ}$ ribbed channel and near the leading edge for the $90^{\circ}$ ribbed channel. The heat transfer coefficients of angled ribbed channels are changed little with rotation, whereas those of the transverse ribbed channel are changed significantly with rotation.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.8
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• pp.401-407
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• 2017

The effect of different rib geometries such as V-shaped continuous (case A), parallel broken (case B), and V-shaped broken (case C) ribs on local heat transfer distributions and pressure drops in a divergent channel with $30^{\circ}$ inclined ribs on one wall or two walls was investigated for Reynolds numbers from 22,000 to 75,000. Top and bottom walls were insulated; two side walls were uniformly heated in the divergent channel. Heated walls were composed of 10 isolated coper sections and length-to-outlet hydraulic diameter ratio of 10. Rib height-to-outlet hydraulic diameter ratio was 0.1, and rib pitch-to-height ratio equaled 10. Results revealed that V-shaped continuous rib (case A) produced approximately 1.4 times higher average Nussselt number than in the parallel broken rib (case B), and V-shaped broken rib (case C) in the channel with two ribbed walls at Re = 54,000.

• The KSFM Journal of Fluid Machinery
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• v.18 no.3
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• pp.66-73
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• 2015

This paper deals with a parametric study on boot-shaped ribs in a rectangular cooling channel. Numerical analysis of the flow and heat transfer was performed using three-dimensional Reynolds averaged Navier-Stokes equations with the Speziale, Sarkar and Gatski turbulence model. The parametric study was performed for the parameters, tip width-to rib width, tip height-to-rib height, rib height-to-channel height, and rib height-to-width ratios. To assess the cooling performance and friction loss, Numsselt number and friction factor were defined as the performance parameter, respectively. The results showed that the cooling performance and friction loss were seriously affected by the four geometric parameters.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2448-2453
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• 2008

The present study numerically investigates the flow and heat transfer characteristics of rib-induced secondary flow in a cooling channel with staggered V-shaped ribs, extruded on both walls. The rib-height-to-hydraulic diameter ration (h/$D_h$) is 0.17; the rib pitch-to-height ratio (p/h) equals 2.8; the Reynolds number is 50,000. Shear stress transport (SST) turbulence model is used as a turbulence closure. The present results are compared with those for a continuous V-shaped rib. Computational results show that, for average heat transfer rate the staggered V-shaped rib gives about 2.5 times higher values than the continuous V-shaped rib, while, for the streamwise pressure drop the former gives about 5 times higher values than the latter. Consequently, for the thermal performances, based on the equal pumping power condition, the staggered one gives about 2 times higher values than the continuous one. Also, for the staggered V-shaped rib, complex secondary flow patterns are generated in the duct due to the snaking flow in the streamwise direction, and more uniform heat transfer distributions are obtained.

• 한국전산유체공학회:학술대회논문집
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• 2002.05a
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• pp.128-133
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• 2002

The heat transfer characteristics of a turbulent flow in a ribbed two-dimensional channel have been investigated numerically. The fully elliptic governing equations, coupled with a four-equation turbulence model, $\kappa-\omega-\bar{t^2}-\epsilon_t$, are solved by a finite volume method of SIMPLE type. Calculations have been carried out for three rib cross-sections : square, triangular, and semicircular, with various rib pitches and Reynolds numbers. The procedure appears to be satisfactory as the results for the square rib compare favorably with available experimental data and earlier calculation. The optimal rib pitch that yields the maximum heat transfer has been identified. It is also found that the square rib is most effective in enhancing the heat transfer. The semicircular rib, on the other hand, incurs the least amount of pressure drop but the improvement in heat transfer is substantially lower.

• Journal of Power System Engineering
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• v.16 no.6
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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.

• The KSFM Journal of Fluid Machinery
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• v.10 no.2 s.41
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• pp.7-15
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• 2007

A numerical procedure for optimizing the shape of three-dimensional channel with V-shaped ribs extruded on both walls has been carried out to enhance the turbulent heat transfer. The response surface based optimization is used as an optimization technique with Reynolds-averaged Wavier-stoked analysis. Shear stress transport (SST) turbulence model is used as a turbulence closure. Computational results for average heat transfer rate show good agreements with experimental data. The objective function is defined as a linear combination of heat transfer and friction loss-related terms with a weighting factor. Three dimensionless variables such as, rib pitch-to-rib height ratio, rib height-to-channel height ratio, and the attack angle of the rib are chosen as design variables. Nineteen training points obtained by D-optimal designs for three design variables construct a reliable response surface. In the sensitivity analysis, it is found that the objective function is most sensitive to the ratio of rib height-to-channel height ratio. And, optimal values of design variables have been obtained in a range of the weighting factor.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.125-130
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• 2008

The present study numerically simulates the flow and heat transfer characteristics of rib-induced secondary flow in a cooling channel with staggered V-shaped ribs, extruded on both walls. The rib pitch-to-height ratio (p/h) varies from 2.8 to 10 with the rib-height-to-hydraulic diameter ration ($h/D_h$) of 0.07 and the Reynolds number of 50,000. Shear stress transport (SST) turbulence model is used as a turbulence model. Computational results show that complex secondary flow patterns are generated in the duct due to the snaking flow in the streamwise direction for all tested cases. In the range of p/h=5 to 10 the staggered V-shaped rib gives about 3 times higher heat transfer augmentation than the reference smooth channel with high heat transfer on both front side and the area around the leading edge of the ribs, while the former cases give about 2.5 times higher streamwise pressure drop than the latter ones. Consequently, for the thermal performances, based on the equal pumping power condition, the staggered ones give about 2 times higher values than the latter ones with more uniform heat transfer distribution.

• The KSFM Journal of Fluid Machinery
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• v.15 no.4
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• pp.19-26
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• 2012

In this paper, a parametric study on ribs which are installed in an equilateral triangular internal cooling channel is presented. The numerical analysis of the flow structure and heat transfer characteristics is performed using three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model. The numerical results are obtained at Reynolds number, 20,000. The parametric study is performed for the parameters, the angle of a rib, rib pitch-to-hydraulic diameter ratio, rib width-to-hydraulic diameter ratio, and rib height-to-hydraulic diameter ratio. The computational results are validated with the experimental data for area-averaged Nusselt number.