• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.11
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• pp.1509-1520
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• 1998

An experiment was carried out for the fully developed turbulent flow of water in tube coils on the condition of uniform heat flux. The present work was conducted for various ranges for Dean number(1794~1321), Prandtl number (2.5~4.5), curvature ratio parameters (22~60). Heat transfer to steady viscous flow in coiled tubes of circular cross section was studied for fully developed velocity and temperature fields under the thermal boundary condition of uniform heat flux. The peripherally local Nusselt number correlated as a function of Dean and Prandtl numbers. We studied the flow in heat coiled tubes under the influence of both centrifugal and buoyancy forces in order to gain insight into the flow pattern. In the present study, we obtained three emperical formulas, $Nu_v=0.0231Re^{0.84}Pr^{0.4}(a/R)^{0.13}$ (vertical) $Nu_c=0.0241Re^{0.86}Pr^{0.4}(a/R)^{0.08}$ (corrugated) $Nu_h=0.0227Re^{0.84}Pr^{0.4}(a/R)^{0.09}$ (horizontal).

• Journal of the Korean Society of Visualization
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• v.18 no.2
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• pp.28-34
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• 2020

In this study, we numerically investigated the thermal stratification in solar seasonal thermal storage tanks. The vertical in/out flows were unsuitable for the thermal stratification in a large scale. The effect of an aspect ratio (AR) on the thermal stratification was investigated. When AR was less than 2, water adheres and flows along the upper wall due to buoyance and the surface effect. Thereafter, hot water flows down and a large scale vortex occurs in entire tank. For high AR, jet flows ejected from the inlet pipe impinges to the opposite wall and splits. The divided flows create two vortex flows in the upper and lower regions. These different flows strongly influence temperature and thermal stratification. The thermal stratification was evaluated in terms of the thermocline thickness and degree of stratification. Compared to ARs, the maximum degree of stratification was obtained with AR of 5 having the minimum thermocline thickness.

• Journal of the Korean Society of Safety
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• v.19 no.3 s.67
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• pp.45-50
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• 2004

4-panel of 1m height and 45cm width were fixed on the $40cm{\times}40cm$ bottom plate and the opening of the panel comer was 5cm. Diameter of stainless vessel is loom and its height is 2cm and it located at the center of the bottom plate. 78mL liquid fuel was filled in the vessel and its depth was 1cm. Flame temperature was measured with K type thermocouple, and radiation heat of flame was measured with heat flux meter. Flame height and its behavior was visualized with video camera. and mass burning rate was measured by fuel combustion time. According to the development of fire, flame swirling was begin. From the experiment the mass burning rate was larger and the height of flame was higher than the usual pool fire flame. Flame temperature and heat flux also increased far more than the pool fire. Consequently the swirling air flow through the openings between the panel and thermal buoyance contribute to increase of heat release rate, flame length and mass burning rate.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.540-545
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• 2008

An atrium has great potential in natural ventilation aided by buoyance effect. Architectural design of an atrium is very critical to maximize the effect. However, it is not easy of an atrium to have optimum shape for natural ventilation, from the aesthetic and economic point of view. Admitting this condition, we suggested a strategy to promote natural ventilation, which can be adopted only with small design change. At first, we installed BIPV on the top of an atrium to strengthen buoyancy effect, and combine forced ventilation by low pressure fan. To evaluate the performance of the measure, CFD simulation and Energy-Airflow analysis were achieved.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.6
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• pp.2046-2056
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• 1996

The constrained melting inside an isothermally heated horizontal cylinder has been repeatedly investigated in many studies only for the moderate Rayleigh numbers. This study extends the range of Rayleigh numbers to systematically investigate the transition during melting processes, especially focusing on the complex multi-cellular flow pattern and thermal instability. The enthalpy-porosity formulation, with appropriate source terms to account for the phase change, is employed. For low Rayleigh numbers, initially developed single-cell base flow keeps the flow stable. For moderate Rayleigh numbers, even small disturbances in balance between thermal buoyance force and viscous force result in branched flow structure. For high Rayleight numbers, Benard type convection is found to develop within a narrow gap between thee wall and the unmelted solid. The marginal Rayleigh number and the corresponding wave number are in excellent agreement with those from linear stability theory.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.5
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• pp.538-544
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• 2012

The bubbles made of hydrogen and oxygen gases producted by electrolysis disturb the electrolysis, but the behavior of these bubbles in the electrolysis stack isn't clearly defined. In order to study on the behavior of bubbles in the flow pattern of the meshes type separator, the flow visualization experiment was performed by using of a visible alkaline electrolysis stack and a stereoscopic microscope. As the results, a fine size bubbles adhered to the separator's surface in the electrolyte solution have grown large sized bubbles until each bubble's buoyance is lager than the sum of surface adhesion force and weight. And then the large bubbles flow into the upper area of the separator. Also, as wide area of the separator have been occupied by various sized bubbles, the electrolysis efficiency is declined.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.1
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• pp.84-90
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• 2013

The hydrogen or oxygen gas producted by electrolysis become many bubbles in the electrolyte, but exact data on the behavior of these bubbles in the separator of an electrolysis stack didn't become known. In this study, the flow visualization experiment on the behavior of bubbles in the flow pattern of the array type separator is performed by using of a visible alkaline electrolysis stack and a stereoscopic microscope. As the results, a fine size bubbles adhered to the surface of the flow pattern grow to large sized bubbles until each bubble's buoyance is lager than the sum of external force and weight. And then the large bubbles flow into the upper area of the separator. Bubbles adhered to the surface of the vertical flow pattern grow quickly than them adhered to the surface of the horizontal flow pattern. Also, he electrolysis efficiency is declined because many multi-size bubbles occupied the wide volume in the flow pattern.

• Journal of the Korean Institute of Gas
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• v.14 no.6
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• pp.1-6
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• 2010

River crossing pipelines have been being operated with buried depth of 1.2~4m underneath river bottom to prevent buoyance and external impact. River crossing pipelines have to show resistance to soil load and hydrostatic pressure. In this study, structural integrity of the river crossing pipeline subjected to soil load and hydrostatic pressure was evaluated by using FE analyses. Hoop stress increased with increasing buried depth under identical water height in case of without concrete encasement, however, hoop stress decreased with increasing water height under identical buried depth.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.879-884
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• 2006

Jinan Poonghyeol in Chonbuk province Is famous for emitting cool air in summer and warm air in winter. Cause for these phenomena is studied by measuring temperature, humidity and air velocity of several locations around Jinan Poonghyeol Temperature variations under the ground are also measured. Analyzing data compiled from July 21, 2005 through May 26, 2006, it is presumed that storage effect of rocks and soil in this area and buoyance effect are the main causes for this mysterious natural air-conditioning phenomena.

• Journal of the Korean Wood Science and Technology
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• v.47 no.1
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• pp.51-65
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• 2019

A wood-plastic composite (WPC) paver block was manufactured using wood chips waste through an extrusion process, and it was intended to be used for paving in basic rest areas. The first stage in this study covered preliminary tests in terms of flexural strength and dimensional swelling to determine the optimal WPC compounding mix condition, by variation of the WPC ingredients. Next, three different paver blocks including the WPC block, a non-porous cement block, and a porous cement block were tested in terms of various material properties in the laboratory. Finally, two outdoor test sections of the proposed paver blocks were prepared to simulate a basic rest area. Test results indicated that the flexural strength of the WPC paver blocks was about 1.6 times greater than that of the tested cement paver blocks. The WPC block pavement was unaffected by water buoyance as well as volume expansion due to swelling. Results from the impact absorbance test and light falling weight deflectometer (LFWD) test clearly showed that the WPC block paving system marginally satisfied the comfortable and safe hardness range from the pedestrians' perspective, while the results demonstrated that it is structurally sound for application as a road paving block.