• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.511-512
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• 2013

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.457-458
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• 2009

• Proceedings of the Korean Nuclear Society Conference
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• 2002.05a
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• pp.264.1-264
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• 2002

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.4
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• pp.440-447
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• 1999

The frosting characteristics on the vertical parallel plates with three cooling plates were experimentally investigated. The experimental parameters were the cooling plate temperature, the air humidity, the air temperature, the air Reynolds number, and the location. The frosting conditions were limited to air temperatures from 10 to $15^{\circ}C$ , air Reynolds numbers from 1600 to 2270, air humidity ratios from 0.00275 to 0.0037kgw/kga and cooling plate temperatures from -10 to $-20^{\circ}C$. Frost growth and density toward the front of the plate were more thick and dense than toward the rear. Frost growth increased with decreasing plate temperature and increasing humidity. In the conditions of the laminar flow, dew point below $0^{\circ}C$and non-cyclic frosting period, frost thickness increased with increasing air temperature. The reason of increasing frost thickness with increasing air temperature was sublimation-ablimation process. The average growth thickness along the locations showed little dependence on the Reynolds numbers.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.6
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• pp.431-439
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• 2001

Recently, multi-room type heat pump system has aroused much attention, because it can achieve much reduction of installation cost and space as well as energy saving in companion with the single room type heat pump system. In the present study, performance characteristics of a 3 room type inverter driven heat pump system, which is widely spread in Japanese market, are measured.. In the single room operation, performances of a heat pump system such s the difference of compressor outlet and inlet pressures and the mass flowrate may increase with the increase of cooling capacity so that COP of the system decrease with the increase of cooling capacity. However, in the 2 room operation, mass flowrate and COP of the total system increase markedly as compared with the single room operation.

• Transactions of Materials Processing
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• v.22 no.3
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• pp.123-132
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• 2013

Hot stamping, which is the hot pressing of special steel sheet using a cold die, can combine ease of shaping with high strength mechanical properties due to the hardening effect of rapid quenching. In this paper, a thermo-mechanical analysis of hot stamping using the finite element method in conjunction with phase transformations was performed in order to investigate the plastic deformation behavior, temperature history, and mechanical properties of the stamped car part. We also conducted a fully coupled thermo-mechanical analysis during the stamping and rapid quenching process to obtain the mechanical properties with the consideration of the effects of plastic deformation and phase transformation on the temperature histories at each point in the part. The finite element analysis could provide key information concerning the temperature histories and the sheet mechanical properties when the phase transformation is properly considered. Such an analysis can also be used to determine the effect of cyclic cooling on the tooling.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.857-868
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• 2005

This paper deals with the accumulated damage in concrete structures due to the cyclic freeze-thaw as an environmental load. The cyclic ice body nucleation and growth processes in porous systems are affected by the thermo-physical and mass transport properties, and gradients of temperature and chemical potentials. Furthermore, the diffusivity of deicing chemicals shows significantly higher value under cyclic freeze-thaw conditions. Consequently, the disintegration of concrete structures is aggravated at marine environments, higher altitudes, and northern areas. However, the properties of cyclic freeze-thaw with crack growth and diffusion of chloride ion effects are hard to be identified in tests, and there has been no analytic model for the combined degradations. The main objective is to determine the driving force and evaluate the reduced strength and stiffness by freeze-thaw. For the development of computational model of those coupled deterioration, micro-pore structure characterization, pore pressure based on the thermodynamic equilibrium, time and temperature dependent super-cooling with or without deicing salts, nonlinear-fracture constitutive relation for the evaluation of internal damage, and the effect of entrained air pores (EA) has been modeled numerically. As a result, the amount of ice volume with temperature dependent surface tensions, freezing pressure and resulting deformations, and cycle and temperature dependent pore volume has been calculated and compared with available test results. The developed computational program can be combined with DuCOM, which can calculate the early aged strength, heat of hydration, micro-pore volume, shrinkage, transportation of free water in concrete. Therefore, the developed model can be applied to evaluate those various practical degradation cases as well.

• Geomechanics and Engineering
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• v.12 no.4
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• pp.707-721
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• 2017

The objective of this paper is to experimentally study the consolidation of saturated silty clay subjected to repeated heating-cooling cycles using a modified temperature-controlled triaxial apparatus. Focus is placed on the influence of the water content, confining pressure, and magnitudes and number of thermal loading cycles. The experimental results show that the thermally induced pore pressure increases with increasing water content and magnitude of thermal loading in undrained conditions. After isothermal consolidation at an elevated temperature, the pore pressure continues to decrease and gradually falls below zero during undrained cooling, and the maximum negative pore pressure increases as the water content decreases or the magnitude of thermal loading increases. During isothermal consolidation at ambient temperature after one heating-cooling cycle, the pore pressure begins to rise due to water absorption and finally stabilizes at approximately zero. As the number of thermal loading cycles increases, the thermally induced pore pressure shows a degrading trend, which seems to be more apparent under a higher confining pressure. Overall, the specimens tested show an obvious volume reduction at the completion of a series of heating-cooling cycles, indicating a notable irreversible thermal consolidation deformation.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.415-418
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• 2011

Thermal fatigue is one of the life-limiting damage mechanisms in the nuclear power plant conditions. The turbulent mixing of fluids of different temperatures induces rapid temperature changes to the pipe wall. The successive thermal transients cause varying cyclic thermal stresses. These cyclic thermal stresses cause fatigue crack nucleation and growth similar to the cyclic mechanical stresses. The aim of this study was to fulfil the need by developing an real crack manufacturing method, which would produce realistic cracks. The test material was austenitic STS 304, which is used as pipelines in the reactor coolant system of a nuclear power plants. In order to fabricate thermal fatigue crack similar to realistic crack, successive thermal transients were applied to the specimen. Thermal transient cycles were combined with heating (60sec) and cooling cycle (30sec). And, In order to identify ultrasonic characteristic, it was performed the ultrasonic reflection measuring method for the fabricated specimen. From the results of ultrasonic reflection measuring testing, it was conformed that A-scan results(average 83% of real crack depth) for the TFC reference specimen was more enhanced NDT reliability than results(average 38% of real crack depth) for the EDM notch reference specimen.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.4
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• pp.303-312
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• 1999

An investigation of the CrMoV rotor steel weldment which experienced by cyclic thermal aging heat treatment and as-received condition was performed. This evaluation was carried out to confirm whether this type of weldment is appropriate for the service environment in terms of microstructural examinations, microhardness measurements and tensile tests. The cyclic thermal aging heat treatment, containing continuous heating and cooling thermal cycle was programmed to simulate the real rotor service condition. The heat treatment was performed for 40 cycles(5920hrs). The results indicated that the weldment was composed of 4 different regions such as heat affected zone of the base metal, butter weld(initial weld), full thickness weld(final weld) and the base metal. The double welding process was applied to eliminate the susceptibility of reheat cracking at heat affected zone of base metal. The grain refinement at the HAZ due to the welding process could reduce the possibility of cracking susceptibility, but its tensile properties was appeared to be low due to the weld metal in as-received condition. The benefit effect, grain refinement was extended with carbides coarsening during the cyclic thermal aging heat treatment. However the poor mechanical properties of the weldment was more degraded as undergoing the heat treatment.