• Progress in Superconductivity
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• v.11 no.1
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• pp.52-56
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• 2009

Temperature distributions and thermal stresses were calculated and analyzed to investigate the effect of the artificial holes to the transient behaviors of the superconductors which was cooled in liquid nitrogen. Three dimensional finite element method was used to calculated the transient temperature and thermal stresses in the superconductors. The cooling speed of the superconductors with holes is faster than those without holes. Because the thermal stresses calculated in the superconductors can be relaxed by the distributed holes, the volume of the peak tensile stress decreases during the cooling in liquid nitrogen. If optimal metal, which can maintain the relaxation of thermal stresses, is used to fill and reinforce the artificial holes, the probability of failure of the superconductors may be decreased by the decrease of volume of peak tensile stress.

• Nuclear Engineering and Technology
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• v.48 no.3
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• pp.660-672
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• 2016

In Part I of this paper, the two-temperature homogenized model for the fully ceramic microencapsulated fuel, in which tristructural isotropic particles are randomly dispersed in a fine lattice stochastic structure, was discussed. In this model, the fuel-kernel and silicon carbide matrix temperatures are distinguished. Moreover, the obtained temperature profiles are more realistic than those obtained using other models. Using the temperature-dependent thermal conductivities of uranium nitride and the silicon carbide matrix, temperature-dependent homogenized parameters were obtained. In Part II of the paper, coupled with the COREDAX code, a reactor core loaded by fully ceramic microencapsulated fuel in which tristructural isotropic particles are randomly dispersed in the fine lattice stochastic structure is analyzed via a two-temperature homogenized model at steady and transient states. The results are compared with those from harmonic- and volumetric-average thermal conductivity models; i.e., we compare $k_{eff}$ eigenvalues, power distributions, and temperature profiles in the hottest single channel at a steady state. At transient states, we compare total power, average energy deposition, and maximum temperatures in the hottest single channel obtained by the different thermal analysis models. The different thermal analysis models and the availability of fuel-kernel temperatures in the two-temperature homogenized model for Doppler temperature feedback lead to significant differences.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.2
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• pp.211-215
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• 2010

Continuous contraction and expansion of disk brake can be due to friction and temperature difference at repeated sudden braking. As serious vibration at disk is produced, the braking force will be changed ununiformly and braking system can not be stabilized. Temperature and heat flux at disk brake are investigated by structural and thermal analysis in this study. The maximum equivalent stress and displacement are shown respectively at the ventilated hole and the lower part of disk plate. At thermal analysis of initial state, temperature on disk plate is distributed from $95.9^{\circ}C$ to $100^{\circ}C$. The maximum heat flux of $0.0168W/mm^2$ is shown at the inner friction part between disk plate and pad. At thermal analysis of transient state, temperature on disk plate is distributed from $95^{\circ}C$ to $96.5^{\circ}C$ after 100 second. The maximum heat flux of $0.0024W/mm^2$ is also shown at the inner friction part between disk plate and pad. By comparing with initial state, the temperature on disk plate is more uniformly distributed and heat flux is more decreased by 7 times at transient state.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.165-169
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• 2008

Binary nanofluids(Binary mixture + nanoparticles) have been extensively paid attention for application in absorption system as a new working fluid. Thermal property evaluation of the new refrigerants is inevitable to apply them for actual system. The objectives of this paper are to measure the thermal conductivity of the binary nanofluids by the transient hot-wire method, and to assess the application possibility of the binary nanofluids for absorption system. It was found that the thermal conductivity of the binary nanofluids ($H_2O/LiBrAl_2O_3$) increased with increasing the concentration of the nanoparticles ($Al_2O_3$) and enhanced up to 27% at 0.1 vol % of the nanoparticles.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.3
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• pp.1-9
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• 1994

The transient temperature distribution of materials during upsetting forming is very important for quality of upsetted workpiece and understanding the thermal characteristics of upsetting is essential for optimum control of the forming. In this paper it is shown that the governing equation of heat transfer for axi-symetric body can be derived from minimizing a functional, and from this theory, formulation of analysis by the finite element method is presented. It is also shown that the thermal contact resistance between two bodies can be represented by equivalent coefficient of heat conductivity. Some examples of calsulated transient temperature distributions by the computer program diveloped from the theory presented in this paper are given in graphic forms. It is proven that the results calculations are very plausible.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.5
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• pp.510-517
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• 2004

A fine hot-wire is used both as a heating element and a temperature sensor in transient hot-wire method. The traditional sensor system is unnecessarily big so that it takes large fluid volume to measure the thermal conductivity. To dramatically reduce this fluid volume, a new sensor fabrication and a data processing method are proposed in this article. Contrast to the conventional and most popular two wire sensor, the new sensor system is made up of divided multiple long and short wires. Through validation experiments, it is found that the measured thermal conductivities of the glycerin are exactly same each other between the conventional and proposed new method. Also some technical considerations in arranging the multiple wires are briefly discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.4
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• pp.341-348
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• 2007

One of the controversial research issues on nanofluids is the temperature dependence of the thermal conductivity of nanofluids, that is, whether it will increase or decrease according to the temperature rise. To evaluate precisely the thermal conductivity behavior of nanofluids, a systematic way of validation experiments for the measuring instrument has been highly recommended. In this paper, procedure of the validation test for transient hot-wire method using the temperature dependence of the base fluids was explained comprehensively and the comparison of the temperature dependence of water-$Al_2O_3$ nanofluids is made between the present work and that of Das et al.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.6 s.249
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• pp.514-522
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• 2006

This study has been performed to predict the transient thermal behavior of the plate in indirectly-fired continuous heat treatment furnace. The temperature profiles in the plate are determined solving the transient one-dimensional heat conduction equations. To verify the validity of the present numerical results, the present results obtained from the transient analysis are compared with those of experiments. Extensive parametric investigations are performed to examine the effects of the emissivities of the plate and refractory, plate thickness and velocity, as well as the gas temperature, on the thermal behavior of the plate.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.210-215
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• 2003

A fine hot-wire is used both as a heating element and a temperature sensor in transient hot-wire method. The traditional sensor system is unnecessarily big so that it takes large fluid volume to measure the thermal conductivity. To dramatically reduce this fluid volume, a new sensor fabrication and a data processing method are proposed in this article. Contrast to the conventional and most popular two wire sensor, the new sensor system is made up of divided multiple long and short wires. Through validation experiments, it is found that the measured thermal conductivities of the glycerin are exactly same each other between the conventional and proposed new method. Also some technical considerations in arranging the multiple wires are briefly discussed.

• Proceedings of the KIEE Conference
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• 1998.07e
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• pp.1644-1646
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• 1998

High-Smokestacks have been the symbol of the thermal power plant. Those cause the thermal power plant to be damaged by lightening for reaching several hundreds meter. In this paper, we investigated the accident of low-voltage source circuit due to grounding potential rise by lightening via high-smokestack in practically driving power plant, described examination into the cause and the impulse analysis. We analysed the transient voltage by EMTP(ElectroMagnetic Transient Program) via modeling the grounding system of power plant. This theoretical results coincided with practical accidental state. Therefore, it was verified that we could apply the grounding system of power plant and substation with the distribution-circuit analysis(EMTP).