• Transactions of Materials Processing
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• v.13 no.8
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• pp.723-730
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• 2004

This paper describes the analysis of extrusion process and integrity for a condenser tube which is a component of the heat exchanger in automobile and all conditioning apparatus. Recently, according to the development of analysis method using the computer, the numerical simulation have been applied to the 3-dimensional hot extrusion process with complex section area of the non-steady statement and then results of the analysis have been applied to optimal die design and process design. In this paper, firstly, the die design was performed for a condenser tube with a multi-hole section and the rigid-plasticity FE analysis performed of extrusion process. Secondly, we estimated metal flow of billet, extrusion load, welding pressure in chamber etc. and evaluated the pressure and elastic strain of the die land and mandrel tooth profile through a stress analysis of the die. Finally, the extrusion test was performed to estimate the validity of FE analysis. This paper confirmed that the designed extrusion die of the research is satisfactorily designed fur integrity of condenser tube.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.378-381
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• 2008

The buckling behavior of cylindrical shape-memory alloy and aluminum tube is investigated at room temperature using a split Hopkinson pressure bar and an Instron hydraulic machine with a specially designed recording system. The shape-memory alloy at superelastic property regime buckles gradually in quasi-static loading, and fully recovers upon unloading. However, the buckling of aluminum tube is sudden and catastrophic, and shows permanent deformation. This gradual buckling of shape-memory alloy is associated with the forward and reverse transformation of stress-induced martensite and seems to have a profound effect on the unstable deformation of tube structures made from shape-memory alloy.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.12
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• pp.1007-1017
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• 2003

An experimental study on the air-side pressure drop and heat transfer coefficient of slit fin-tube heat exchanger has been carried out. The data reduction methodology for air-side heat transfer coefficients in the literature is not based on a consistent approach. This paper focuses on new method of data reduction to obtain the air-side performance of fin-tube heat exchanger using R22 and recommends standard procedures for dry and wet surface heat transfer estimation in fin-tube heat exchanger having refrigerant on the tube-side. Results are presented as plots of friction f-factor and Colburn j -factor against Reynolds number based on the fin collar outside diameter and compared with previous studies. The data covers a range of refrigerant mass fluxes of 150∼250 kg/$m^2$s with air flows at velocity ranges from 0.3 m/s to 0.8 m/s.

• Journal of computational fluids engineering
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• v.12 no.3
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• pp.13-19
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• 2007

A numerical simulation on the heat transfer and flow field was carried out to improve the performance of the shell and tube heat exchanger. The steady incompressible 3-D Navier-Stokes solution is obtained with the actual operational condition and geometry of the heat exchanger. Based on this study, it is noted that the present geometry of the heat exchanger causes poor heat transfer since the air inside shell does not flow through the tube bundle, but around it. The enhancement of the heat transfer can be achieved by the variation of the design factor like the sealing strip located on the top/bottom and middle of the baffle, but it causes the increasement of the pressure drop. In this paper, the effects of the location and size of the sealing strips and flow rate through the heat exchanger on the heat transfer and pressure drop are studied.

• Transactions of Materials Processing
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• v.12 no.3
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• pp.214-220
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• 2003

In the case of hollow cylinder extrusion using porthole die, the effects of extrusion parameters-temperature, the speed of extrusion, the shape of the die and mandrel-on metal flow in porthole die extrusion of aluminum have been investigated. There have been few studies about condenser tube extruded by porthole die. This study was designed to evaluate metal flow, welding pressure, extrusion load, tendency of mandrel deflection according to variation of chamber length in porthole die. The welding chamber height in condenser tube was calculated by using finite element method. Forming analysis results for condenser tube would provide useful information for the optimal design of porthole die.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.365-367
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• 2010

In this paper, we presented the exact Riemann solver for the air-water two-phase shock tube problems where the strength of the propagated sock wave is moderately weak. The shock tube has a diaphragm in the middle which separates water medium in the left and air medium in the right. By rupturing the diaphragm, various waves such as rarefaction wave, shock wave and contact discontinuity are propagated into water and air. Both fluids are treated as compressible, with the linearized equations of state. We used the isentropic relations for the air and water assuming a weak shock wave. We solved the shock tube problem considering a high pressure in the water and a low pressure in the air. The numerical results cleary showed a left-traveling rarefaction wave in the water, a right-traveling shock wave in the air, and the right-traveling material interface.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.5
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• pp.398-410
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• 2001

The flow and heat transfer characteristics for three-dimensional mixed convection flows in a radiator flat tube with U--shaped grooves are analyzed numerically. The flow and temperature fields are calculated by using the modified SIMPLE algorithm for irregular geometry. One tube specification among the various flat tube exchangers is recommended by considering the heat transfer and pressure drop. The effects of variation of coolant flow conditions and external air conditions on the flow and the thermal characteristics for the selected tube are investigated. the results show that inlet velocity of coolant flow is the very important factor in heat transfer and pressure drop, and top side is better position than the others as fin cleave to tube.

• 연구논문집
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• s.30
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• pp.121-128
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• 2000

The failed tube received for this study has been used for approximately 10 year at $330^{\circ}C$ in a steam production boiler tube was fractured in the transversed direction to tube length, and fracture mode was typically intergranulas type without the plastic deformation. The fracture surface was covered by the oxide scale formed from the intermal high pressure steam at high temperature. The microstructure was not nearly thermal-degraded during the service. From this result, we can conclude that the oxide film was proferentialy formed into the grainboundary and this grainboundary oxide film was brittle-fractured by the thermal stress in the longitudinal direction to the tube brittle intergranular fracture mode.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.3
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• pp.220-229
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• 2003

An experimental study on the air-side pressure drop and heat transfer coefficient of slit fin-tube heat exchanger has been carried out. The data reduction methodology for air-side heat transfer coefficients in the literature is not based on a consistent approach. This paper focuses on new method of data reduction to obtain the air-side performance of fin-tube heat exchanger using R22 and recommends standard procedures for dry surface heat transfer estimation in fin-tube heat exchanger having refrigerant on the tube-side. Results are presented as plots of friction f-factor and Colburn j -factor against Reynolds number based on the fin collar outside diameter and compared with previous studies. The data covers a range of refrigerant mass fluxes of 150~250 kg/$m^2$s with air flows at velocity ranges from 0.6 m/s to 1.6 m/s.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.1
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• pp.20-32
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• 1992

A numerical solution for heat transfer in the flue tube of a pulse combustion water heater was presented. The $k-{\varepsilon}$ turbulent model was adopted to describe turbulent characteristics and radiative heat transfer was calculated by P-N approximation. Three pulsating conditions equivalent to existing experimental studies were used for analysis. Pulsating pressure was specified at the inlet and outlet of flue tube and numerical procedure using control volume method and pressure boundary condition was presented. It was found that the present mathematical model and numerical method could predict effectively the flow field and heat transfer for the flue tube in pulse combustor.