• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.333-336
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• 2006

A new forming method for metal/ other metal two-layer tubes by multi-billet extrusion (MBE) is introduced. The forming possibilities of two-layer tubes CDA 365(inner)/Al 1100(outer) and Al 2014(inner)/Al 1100(outer) by MBE are investigated according to the given frictional condition and die profile. The results show that two-layer tube composed by two types tube as abovementioned can be manufactured by MBE. Some stated variables in the forming process such as effective stress and normalized pressure at welding surface are analyzed by FEM code ($DEFORM^{TM}$-3D)

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2443-2453
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• 1994

The structure of turbulence of fully developed flow through four concentric annuli with the rough outer wall was investigated experimentally for a Reynolds number range Re=15, 000-93, 000. Turbulence intensities were measured in three(u, v, w) directions, and turbulence shear stresses in annuli of radius=0.13, 0.26, 0.4 and 0.56, respectively. Due to the square roughness element attached periodically along the axial direction, the radial velocity fluctuations show similar distribution regardless of the different .alpha.cases. However, the axial and circumferential velocity fluctuation profiles demonstrate the longitudinal turbulence structures are strongly influenced by the .alpha. values. The turbulent eddy viscosity deduced form mean velocity distributions and the measured Reynolds shear stresses are also presented and discussed.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1542-1547
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• 2003

This paper represents the solar collector performance with type of an evacuate double glass, and a copper tube was installed in center of collector to get a solar thermal energy. The one module of solar collector and artificial sun were used in this experiment The distance between artificial sun and solar collector was fixed at 0.5m, and this experimental condition was focused on winter season. The experiments were carried out. three times for getting a accurate data and the heat amount of one module evacuate d solar collector was estimated at out. 48 kcal/hr.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1749-1757
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• 1995

The structure of turbulence of fully developed flow through three concentric annuli with both rough inner and outer walls was investigated experimentally for Reynolds number range Re=15000-93000. Turbulence intensities were measured in three (u, v, w) directions, and turbulence shear stresses in annuli of radius ratios .alpha.= 0.26, 0.4 and 0.56, respectively. The result showed that the structure of turbulence for these asymmetric flows was not the same as that for the annulus with smooth walls. The velocity fluctuations of all three components (u, v, and w-directions) showed little discernible variation with Reynolds numbers, but became apparent with the influence of radius ratio (.alpha.) The experimental results for an annulus with the roughened outer wall and a smooth annulus were shown in the figures as a reference. The eddy diffusivities and friction factors were also presented and discussed.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.6
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• pp.103-111
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• 2001

During cold-start period, the reduction of exhaust emissions is a challenging task. To decrease harmful gaseous substances such as HC, it is necessary to realize a fast catalyst warm-up. In this study, the performance of dual pipe exhaust system have been carried out through different test mode. From measurement of gas temperature and HC concentration, the following conclusions were derived ; 1) Compared with single pipe, dual pipe exhaust system remarkably increase temperature of exhaust gas going through M.C.C(Main Catalytic Converter). 2) W.C.C.(Warm-up Catalytic Converter) also decreases HC emission. To reduce HC emission, it is helpful to use W.C.C. as well as dual pipe exhaust system. 3) Using finite element method, it is shown that inner parts have much higher distribution of temperature than outer parts.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.511-516
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• 2005

This study is to investigate the pressure wave characteristics and the maximum pressure rise generated by instantaneous valve closure at the end of the straightening polybutylene double piping system with header. Experiments were conducted under the following conditions: initial pressure $1{\sim}5$ bar, flow velocity $0.5{\sim}3.0$ m/s and water temperature $25^{\circ}C$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.4
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• pp.462-471
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• 1997

The water-to-air heat pump system requires relatively lower energy consumption and less installation space. The heat exchangers used for this system are the finned-tube type for the indoor unit and the double-tube type for the outdoor unit. Mathematical models for this system are developed and programmed in computer. Experimental data from various conditions are obtained and compared with calculated values from the computer simulation program. Differences of cooling capacity and COP are 1.25% and 0.47%, and those of heating capacity and COP are 0.51% and 0.13%, respectively. Simulation results are in good agreement with test results. Therefore, the developed program is effectively used for the design and the performance prediction of water-to-air heat pump system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.81-88
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• 1995

Fully developed turbulent flow through three concentric annuli with both the rough inner and outer walls was experimentally investigated for a Reynolds number range Re=15,000-85,000. Measurements were made of the pressure drop, the positions of zero shear stress and maximum velocity, and the velocity distributions in annuli of radius ratios, ${\alpha}=0.26$, 0.4 and 0.56, respectively. The experimental results showed that the positions of zero shear streess and maximum velocity were only weakly dependent on the Reynolds number. It was also found that the position of zero shear stress was not coincident with that of maximum velocity. Furthmore, the former was influenced more sensitively than the latter on the square-ribbed roughness along the axial direction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.7
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• pp.380-385
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• 2009

This study is to investigate the pressure wave characteristics and the maximum pressure rise generated by instantaneous valve closure at the end of the straightening polybutylene double piping system with header. Experiments were conducted under the following conditions: initial pressure $0.1{\sim}0.5$ MFa, flow velocity $0.5{\sim}3.0$ m/s and water temperature $25^{\circ}C$.

• Geotechnical Engineering
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• v.23 no.6
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• pp.33-38
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• 2007