• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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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.

• Journal of Power System Engineering
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• v.9 no.1
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.3 s.234
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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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.6
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• pp.514-520
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• 2005

Surface heat transfer of a fully developed turbulent air flow in a $45^{\circ}$ inclined ribbed square duct with two and four heating walls was experimentally investigated, at which the experimental works were peformed for Reynolds numbers ranging from 7,600 to 26,000. The pitch-to-rib height ratio, p/e, was kept at 8 and rib-height-to-channel hydraulic diameter ratio, $e/D_h$ was kept at 0.0667. The channel length-to-hydraulic diameter ratio, $L/D_h$ was 60. The heat transfer coefficient values were decreased with the increase in the number of heat-ing walls. Results of this investigation could be used in various applications of internal channel turbulent flow involving roughened walls.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.383-389
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• 2016

Based on a surface design with rectangular cavities and channels, we investigated the effects of gravity and capillary pressure on pool-boiling Critical Heat Flux (CHF). The microcavity structures could prevent liquid flow by the capillary pressure effect. In addition, the microchannel structures contributed to induce one-dimensional liquid flow on the boiling surface. The relationship between the CHF and capillary flow was clearly established. The driving potentials for the liquid supply into a boiling surface can be generated by the gravitational head and capillary pressure. Through an analysis of pool boiling and visualization data, we reveal that the liquid supplement to maintain the nucleate boiling condition on a boiling surface is closely related to the gravitational pressure head and capillary pressure effect.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.29-30
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• 2005

A three-dimensional numerical calculation has been performed to investigate mixed convective vortex flow in rectangular channels(width/height=4) with the upper part cooled and the lower part heated uniformly. In this study, the Prandtl number was 909, the Reynolds number was varied from 0 to $9.6{\times}10^{-2}$ and the Rayleigh number from $10^3$ to $5{\times}10^4$. The governing equations were discretized using the finite volume method. From a parametric study, velocity and temperature distributions were obtained and discussed. It is found that vortex flow of mixed convection in rectangular channels can be classified into three flow patterns which depend on Reynolds and Rayleigh numbers, and the regular vortex structure disappears around Rayleigh number $5{\times}10^4$.

• Journal of Power System Engineering
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• v.20 no.6
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• pp.51-57
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• 2016

Experiment is carried out to investigate the mixed convective flow in three-dimensional horizontal rectangular channels filled with high viscous fluid. The particle image velocimetry(PIV) with thermo-sensitive liquid crystal tracers is used for visualizing and analysis. Quantitative data of temperature and velocity are obtained by applying the color-image processing to a visualized image, and neural network is applied to the color-to-temperature calibration. In this study, the fluid used is silicon oil(Pr=909), the aspect ratio(channel width to heigh) is 4 and Reynolds number is $2{\times}10^{-2}$. From the present study, we can visualize the quantitative temperature and velocity of mixed convective flow in three-dimensional horizontal rectangular channels simultaneously.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.210-215
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• 2005

A three-dimensional numerical simulation is performed to investigate on a low Reynolds number mixed convection in a horizontal rectangular channel with the upper part cooled and the lower part heated uniformly. The three-dimensional governing equations are solved using a finite volume method. For convective term, the central differencing scheme is used and for the pressure correction, the PISO algorithm is used. Solutions are obtained for A=4, Pr=0.72, 10, 909, the Reynolds number ranging from $2.1{\times}10^{-2}$ to $1.2{\times}10^{-1}$, the Rayleigh number is $3.5{\times}10^4$. It is found that vortex roll structures of mixed convection in horizontal rectangular channel can be classified into three roll structures which affected by Prandtl number and Reynolds number.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.10
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• pp.773-778
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• 2015

The local heat transfer and pressure drop of developed turbulent flows in convergent/divergent channels with square axial cross-sectional areas were experimentally investigated to improve the channel design, such as a gas turbine cooling system. Square convergent/divergent channels with one ribbed wall were manufactured with a fixed rib height e of 10 mm and a ratio of rib spacing p to height e of 10. The measurement was conducted for Reynolds numbers from 15,000 to 89,000. Convergent, divergent, and straight channels with ratios $D_{ho}/D_{hi}$ of 0.75, 1.33, and 1.0, respectively, are considered. Of the three channel types, the ribbed divergent channel was found to produce the best thermal performance under identical flow rate, pumping power, and pressure loss conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.3
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• pp.173-179
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• 2016

This is a numerical study on the curved channel type of hydrogen reformer using the commercial code of fluid dynamics. We numerically compared the numerical model in a previous study model and the modelling of a tube type curved channel. In the result of numerical analysis on 4 types of curved channel reformers, the methanol conversion efficiency of type 1~4 were 45.0%, 45.3%, 45.6%, 45.6% respectively, and there was hardly any difference by ${\pm}0.6%$. In light of flow characteristics, the rectangle type tube and the type 2 with $45^{\circ}$ turn showed most uniform flow characteristics and concentration distribution of methanol, and the circular type tube and the type 3 with $90^{\circ}$ turn had most un-uniform flow characteristics and concentration distribution of methanol. We concluded that the design for curved channel reformer has to have rectangle type tube with curve of almost $45^{\circ}$ as in the type of curved pipe with $45^{\circ}$ turn.