• Proceedings of the KSME Conference
• /
• 2000.04a
• /
• pp.103-108
• /
• 2000

Since the ceramic/metal joint material is made at a high temperature, the residual stress development when it is cooled from bonding temperature to room temperature due to remarkable difference of thermal expansion coefficient between ceramic and metal. As residual stress at ceramic/metal joints influences the strength of joints, it is important to estimate residual stress quantitatively. In this study, it is attempted to estimate joint residual stress of $Si_3N_4/STS304$ joints quantitatively and to compare the strength of Joints. The difference of residual stress is measured when repeated thermal cycle is loaded under the conditions of the practical use of the ceramic/metal joint. And 4-point bending test is performed to examine the influence of residual stress on fracture strength. As a residual it is known that the stress of joint decreases as the number of thermal cycle increases.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.2
• /
• pp.680-688
• /
• 1996

In this paper, the unsteady state calculational model is proposed for the thermal stratification analysis in the feedwater line of the PWR plant. By defining dimensionless parameters in the two-dimensional polar coordinate system and applying SIMPLE algorithm, the temperature and flow profiles due to the thermal stratification are obtained. Base on the fact that the most significant condition occurs when the fluid temperature difference between the piping ends reaches as high as 166.deg. C, the present result shows that max. Dimensionless temperature difference of 0.6 (about l00.deg. C) obtained between hot and cold sections of pipe wall at dimensionless time 47.0.

• Journal of the Korean Society for Precision Engineering
• /
• v.9 no.4
• /
• pp.44-57
• /
• 1992

Ball screw systems have been used for positioning elements of machine tools and precision tables. In order to maintain the high rigidity and accuracy, a certain amount of preload is applied between the nut and the screw of ball screw systems. However, large amount of the preload oncreases the frictional heat. The temperature rises remarkably at the high speed motion, and the thermal expansion degrades the positioning accuracy. In this paper, a finite difference method is applied to analyse temperature distributions and thermal expansions of the ball screw system according to preload conditions and rotational speeds. Some simulation results show that the developed methodology is appropriate to study the thermal expansion characteristics of ball screw systems.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.19 no.4
• /
• pp.459-479
• /
• 2015

Two-dimensional steady laminar natural convection around a heat conducting and generating solid body inside a square enclosure with different thermal boundaries is performed. The mathematical model is governed by the coupled equation of mass, momentum and energy. These equations are discretized by finite volume method with power-law scheme and solved numerically by SIMPLE algorithm with under-relaxation technique. Effect of Rayleigh number, temperature difference ratio of solid-fluid, aspect ratio of solid-enclosure and the thermal conductivity ratio of solid-fluid are investigated numerically for Pr = 0.7. The flow and heat transfer aspects are demonstrated in the form of streamlines and isotherms respectively.

• Proceedings of the SAREK Conference
• /
• 2006.06a
• /
• pp.1144-1149
• /
• 2006

Electric power is generated by Seeback Effect if there is thermal difference in pettier module. Peltier module is composed by alumina, Bi-Te semiconductor and insulation (or air). If load is increased in pettier module, the alumina of module will be destroyed. One of the preventing method of module destruction is using damper between module and heat source. But the electric Power is dropped because of decrease of thermal difference, if thermal conductivity of damper was tourer than other thermoelectric materials. We design, Polymer Pad for enhancing thermoelectric porter. As the result of these experiment, Polymer Pad is more superior than the Rubber in the stability and thermal conduction.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.17 no.8
• /
• pp.893-897
• /
• 2004

In this paper, we studied the mechanical and thermal properties on slice XLPE sheet from 22 kV and 154 kV power cables. Interface structures are XLPE/semiconductor and XLPE/water/semiconductor. We evaluated mechanical property, thermal analysis, moisture analysis. Based on mechanical and thermal properties of the 22 kV XLPE sheet, elongation, mechanical strength, and melting point were evaluated to be 485.48 %, 1.74 kgf/$\textrm{mm}^2$ and $102.48^{\circ}C$, respectively. It was also evaluated from the mechanical and thermal properties of 154 kV XLPE sheet that elongation, mechanical strength, and melting point are 507.81 %, 1.8 kgf/$\textrm{mm}^2$, $106.9^{\circ}C$, respectively. A region shows a rapid increase in tension strength, and B region only shows increase in elongation under 1.0 kgf/$\textrm{mm}^2$, C region shows increase in both elongation and tension strength. Difference of melting point came from the chain of XLPE polymer and the difference of crystallization. Moisture density of semiconductor showed 800 ∼ 1200 ppm before extrude, 14000 ∼24000 ppm after extrude. These values were higher than the moisture density of XLPE (300∼560) ppm.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.20 no.5
• /
• pp.541-546
• /
• 2011

This study was numerically investigated on thermal deformation of AC4C and AC7A aluminum alloy casting material for manufacturing the automobile tire mold. The metal casting device was used in order to manufacture the mold product of automobile tire at the actual industrial field. The temperature distribution and the cooling time of these materials were numerically calculated by finite element analysis. Thermal deformation with stress distribution was also calculated form the temperature distribution results. The thermal deformation was closely related to the temperature difference between the surface and inside of the casting. As shown by numerical analysis result, the thermal deformation of AC7A casting material became higher than AC4C casting material. In addition, the results of displacement and stress distributions appeared to be larger at the center parts of casting than on its sides because of the shrinkage caused by the cooling speed difference.

• Journal of IKEEE
• /
• v.18 no.4
• /
• pp.532-535
• /
• 2014

This paper analyzed thermal characteristics of super junction MOSFET using process and design parameters. Trench process is very important to super junction MOSFET process. We analyzed the difference of temperature, thermal resistance, total power consumption according to trench etch angle. As a result we obtained minimum value of temperature difference and thermal resistance at $89.3^{\circ}$ of trench etch angle. The electrical characteristics distribution of super junction MOSFET is not showed tendency according to trench etch angle. We need iterative experiments and simulation for optimal value of electrical characteristics. The super junction power MOSFET that has superior thermal characteristics will use automobile and industry.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.33 no.8
• /
• pp.573-579
• /
• 2009

A thermal mass air flow sensor, which consists of a micro-heater and thermal sensors on the silicon-nitride thin membrane structure, is micro-fabricated by MEMS processes. Three thermo-resistive sensors, one for the measurement of microheater temperature, the others for the measurement of membrane temperature upstream and downstream of the micro-heater respectively, are used. The micro-heater is operated under the constant temperature difference mode via a real time controller, based on inlet air temperature. Two design models for microfabricated flow sensor are compared with experimental results and confirmed their applicabilities and limitations. The thermal characteristics are measured to find the best flow indicator. It is found that two normalized temperature indicators can be adopted with some advantages in practice. The flow sensor with this control mode can be adopted for wide capability of high speed and sensitivity in the very low and medium velocity ranges.

• Solar Energy
• /
• v.19 no.4
• /
• pp.11-20
• /
• 1999

The study on ice thermal storage system is to improve total system performance and increase the economical efficiency in actual air-conditioning facilities. To obtain the high charging and discharging efficiencies in ice thermal storage system, the improvement of thermal stratification is essential, therefore the process flow must be piston flow in the cylindrical type. In the influence of the inlet port type, the inflowing water in the distributor type diffuses through the whole storage tank more than in the slot type. In case of the flow process in the ice storage tank, the upward flow type in the charging process and the downward flow type in the discharging process make the stratification well, thereby the loss of energy wored be smaller. The influence of the inlet temperature difference and the change of the inlet flow rate is intensive when the temperature difference is larger, the flow rate is smaller in case of charging and the results are opposite in case of discharging with the reason that the good coduction condition. The total effeciency of the ice thermal storge system is 73% on condition that the porosity in the thermal storage tank is 0.55. This result shows that cylinderical ice storage tank has better storage capacity than rectangular type in case of the same porosity.