• Journal of Mechanical Science and Technology
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• v.20 no.1
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• pp.158-166
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• 2006

Extended Graetz problem in microtube is analyzed by using eigenfunction expansion to solve the energy equation. For the eigenvalue problem we applied the shooting method and Galerkin method. The hydrodynamically isothermal developed flow is assumed to enter the microtube with uniform temperature or uniform heat flux boundary condition. The effects of velocity and temperature jump boundary condition on the microtube wall, axial conduction and viscous dissipation are included. From the temperature field obtained, the local Nusselt number distributions on the tube wall are obtained as the dimensionless parameters (Peclet number, Knudsen number, Brinkman number) vary. The fully developed Nusselt number for each boundary condition is obtained also in terms of these parameters.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.952-961
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• 1989

The purpose of this study is to investigate the behavior of operational and design factors on the performance characteristics of a horizontal fin-tube heat exchanger under phase change conditions for refrigerant. The flow and heat transfer in the heat exchanger are simulated numerically taking into account the variations of heat transfer coefficients, thermodynamic and flow properties of refrigerant, and the axial heat conduction in the tube wall. As the results of this study, it was found that the annular flow model was more reasonable physically than the homogeneous one for the two phase flow of refrigerant and axial heat conduction of tube wall did not have a great influence on the analysis. The effects of refrigerant pressure, mass flow rate of air, diameter of tube and the number of fins per unit length of tube were also discussed.

• Proceedings of the Korean Nuclear Society Conference
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• 2001.05a
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• pp.192.1-192
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• 2001

• Journal of Welding and Joining
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• v.17 no.5
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• pp.77-82
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• 1999

Resistance spot welding process is completed in very short time and there are many factors affecting on the generation of heat. It is difficult to control these experimental factors and monitor distribution of the temperature and stresses in the experimental analysis case. and too much time and expense are required for the experimental trials to fine proper welding condition. So numerical analyses have been attempted steadily, but most numerical analyses on the resistance spot welding are mainly focused on thermal behavior. Therefore, in this paper, the numerical analysis of mechanical behavior as well as heat conduction is carried out for the spot welding process. For this numerical analysis, axial symmetric computer program for the spot welding analysis by F.E.M. has been developed considering heat conduction and thermal elastic-plastic theory. Material properties depending on temperature such as density, heat conductivity, heat expansion coefficient, specific heat, yield stress, elastic modulus, and specific resistance are considered. Using the results of temperature distribution obtained from heat conduction analysis, the thermal elastic-plastic analysis is carried out to clarify mechanical behavior of spot welded specimen. In order to evaluate the effect of residual stresses, numerical analyses are carried out under tension-shear load in two cases respectively; one with residual stress, the other without residual stresses.

• Journal of Welding and Joining
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• v.21 no.6
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• pp.40-45
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• 2003

Steel members have advantages of resisting torsion and axial compression. In design, residual stresses at the welded joint of T-shape steel pipes are one of the most important points to be considered. In this paper, characteristics of residual stresses of welded joints are clarified by carrying out 3D non-steady heat conduction analysis and 3D thermal elastic-plastic FE-analysis. According to the results, the production mechanism of residual stresses at the welded joint of T-shape steel pipe is clarified. In this paper, circumferential stresses depended on thermal histories but axial and radial stresses were more dependent on geometrical shape than thermal histories. Residual stresses in the axial direction on the lower part of pipe member were tensile, controlled by geometrical shape. However, in case of middle part, residual stresses in all the directions were controlled by thermal histories.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.18 no.2
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• pp.221-227
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• 2009

The study of the solidification process of welded metal is carried out using the finite element method, which is the basic study for optimal design. In the analysis of temperature, the welded zone is cooled as the result of heat conduction to the base metal and heat transfer to the circumference. In the early phase of the temperature in base metal zone is little changed. But after the rise in temperature the whole area is cooled gradually and uniformly with the lapse of 10 seconds, and a temperature change is hardly occurred in the radial direction but in the axial direction.

• Nuclear Engineering and Technology
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• v.29 no.5
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• pp.406-416
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• 1997

A computational method is developed for predicting the steady-state temperature field in an LMR core. Detailed core-wide coolant temperature profiles are efficiently calculated using the simplified energy equation mixing model[1] and the subchannel analysis method. The $\theta$-method is employed for discretizing the energy equations in the axial direction. The interassembly coupling is achieved by interassembly gap flow. Cladding and fuel temperatures are calculated with the one-dimensional conduction model and temperature integrals of conductivities. The accuracy of the method is tested by performing several benchmark calculations for too LMR problems. The results indicate that the accuracy is comparable to the other methods based on ENERGY model. It is also shown that the implicit scheme for the axial discretization is more efficient than the explicit scheme.

• Journal of the Korean Vacuum Society
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• v.17 no.5
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• pp.400-407
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• 2008

In this study, Two dimensional spatial profile of electromagnetic field for capacitively coupled plasma source is calculated. Based on one dimensional fluid equation, spatial profile for the axial direction of electric field and conduction current density is firstly calculated. The two dimensional spatial profile for the electromagnetic field is calculated from solution of Maxwell equation that is expanded to power series for ${\omega}r/c$ into the radial direction.

• Solar Energy
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• v.6 no.1
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• pp.60-69
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• 1986

Two-dimensional finite difference numerical analysis is used to study conjugate natural convection heat transfer from a horizontal conducting tube with one vertical axial fin. By increasing dimensionless fin length ($L_F$), the mean total Nusselt number of the upward fin is slightly less than that of the downward fin at $L_F\;{\le}\;0.18$ and is higher than that of the downward fin at $L_F\;>\;0.18$. However comparing the upward fin and the downward fin with the no fin, the mean total Nusselt numbers of downward fin and upward fin at $L_F=0.30$ are increased approximately 4.01% and 5.51%, respectively. As Rayleigh number, Prandtl number and Biot number increase, the mean total and the mean tube Nusselt numbers are increased, but as wall thickness increases, the mean total and the mean tube Nusselt numbers are decreased. As the fin conduction parameter increases, the mean total Nusselt number is slightly increased because of increasing the mean fin Nusselt number.

• Tribology and Lubricants
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• v.11 no.5
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• pp.150-155
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• 1995

In order to analyze the thermal effects of the rotor models, the finite element technique was used in this study. The length of the hat was investigated as a design parameter. At the start of each brake application the disk surface temperature rapidly increases to a maximum value and then decays due to external cooling and thermal conduction to the hat. The calculated results indicate that the long length of the hat shows the minimum deformation in axial direction, which is related to the thermal problems, coned wear, vibration and noise.