• Journal of Mechanical Science and Technology
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• v.19 no.5
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• pp.1206-1215
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• 2005

The thermal stratification phenomena, frequently occurring in the component of nuclear power plant system such as pressurizer surge line, steam generator inlet nozzle, safety injection system (SIS), and chemical and volume control system (CVCS), can cause through-wall cracks, thermal fatigue, unexpected piping displacement and dislocation, and pipe support damage. The phenomenon is one of the unaccounted load in the design stage. However, the load have been found to be serious as nuclear power plant operation experience accumulates. In particular, the thermal stratification by the turbulent penetration or valve leak in the SIS and SCS pipe line can lead these safety systems to failure by the thermal fatigue. Therefore in this study an 1/10 scaledowned experimental rig had been designed and installed. And a series of experimental works had been executed to measure the temperature distribution (thermal stratification) in these systems by the turbulent penetration, valve leak, and heat transfer through valve. The results provide very valuable informations such as turbulent penetration depth, the possibility of thermal stratification by the heat transfer through valve, etc. Also the results are expected to be useful to understand the thermal stratification in these systems, establish the thermal strati­fication criteria and validate the calculation results by CFD Codes such as Fluent, Phenix, CFX.

• Laser Solutions
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• v.12 no.2
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• pp.17-25
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• 2009

Two methodologies for predicting thermal relaxation time of tissue subjected to pulsed laser irradiation is introduced by the calculation the optical penetration depth and by the investigation of the temperature diffusion behavior. First approach is that both x-axial and y-axial thermal relaxation times are predicted and they are superposed to achieve the thermal relaxation time (${\tau}_1$) for two-dimensional square tissue model. Another approach to achieve thermal relaxation time (${\tau}_2$) is measuring the time required for local temperature drop until $e^{-1}$ of the maximum laser induced heating.

• Progress in Superconductivity and Cryogenics
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• v.4 no.2
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• pp.68-72
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• 2002

This work investigates the transient cooling characteristics of an Infrared (IR) detector cryochamber, which has a critical effect on the cooling load. The current thermal modeling considers the conduction heat transfer through a cold well. the gaseous conduction due to outgassing. and the radiation heat transfer. The transient cooling Performance. i.e. the penetration depth and cooling load, is determined using a finite difference method. It is found that the penetration depth increases as the bore conductivity increases. Gaseous conduction and radiation hardly affect the penetration depth. The transient cooling load increases as the bore conductivity increases. The effects of gaseous conduction and radiation on transient heat transfer are weak at initial stages of cooling. However, their effects become significant as the cooling Process Proceeds.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.8
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• pp.409-417
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• 2015

A simplified rotary heat-exchanger model was developed with an assumption of a linear temperature distribution along the flow direction. Based on the model, the exact fluid solution and solid temperature variations were obtained and verified from a comparison with previous numerical studies. The heat transfer in the rotary heat exchanger was investigated using the theoretical solutions. The heat exchanger's effectiveness was shown to be saturated, with a rotational-speed increase that is higher than a critical value that is solely dependent on the thermal capacity of the solid matrix but independent of the fluid flow rate; the saturated value of the effectiveness was determined only by the NTU of the heat exchanger. Where the thermal diffusivity of the solid matrix is so slight that the thermal penetration depth becomes smaller than the matrix thickness, the effective thermal capacity of the solid matrix decreased according to the penetration depth.

• Journal of Welding and Joining
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• v.23 no.1
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• pp.48-54
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• 2005

Laser keyhole welding is investigated using a three-dimensional Gaussian heat source, and the heat source parameters such as the keyhole depth, welding efficiency and power density distribution factor are determined in a systematic way. For partial penetration, the keyhole depth is same as the penetration and is predicted using the experimental data. The welding efficiency is calculated using the ray-tracing method and the power density distribution factor is determined from the bead shape. Full penetration is classified into the transition, normal and excessive modes depending on the degree of keyhole opening. Thermal analysis of the bead-on-plate welds is conducted using the Gaussian heat source, and the calculated weld geometries show reasonably good agreements with the experimental results.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.2
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• pp.48-54
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• 2002

Since photocatalysts are activated by lights of UV wavelengths, plasma is alternatively used as a light source for a photocatalytic reactor. Light intensity generated by plasma is proportional to the surface area of catalytic material, and this, in many practical applications, is prescribed by the geometry of a plasma generator. Thus, it is crucial to increase the surface area far sufficient light intensity for photocatalytic reaction. For example, in a pack-bed type reactor, multitudes of beads are used as a substrate in order to increase the surface area. Honeycomb monolith type substrate, which has very good surface area to volume ratio, has been difficult to apply plasma as a light source due to the fact that light penetration depth through the honeycomb monolith was too short to cover sufficient area, thus resulting in poor intensity for photocatalytic reaction. In this study, nonthermal plasma generation through a photocatalytic reactor of honeycomb monolith substrate is investigated to lengthen this short penetration depth. The ceramic honeycomb monolith substrate used in this study has the same length as a three way catalyst used fur automotive applications, and it is shown that sufficient light intensity for photocatalytic reaction can also be obtained with honeycomb monolith type reactor.

• Journal of Power System Engineering
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• v.7 no.2
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• pp.73-79
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• 2003

The present study was aimed at analysing the damage of a used gas turbine bucket after 39,500h of total service. Microstructures and cracks of service-induced bucket were observed. The crack might have initiated from the coating in the bucket surface by thermal fatigue and propagated into the GTD111 base metal. Maximum depth of penetration was 2.7 mm(full penetration) at the leading edge. Crack contains a lot of Cr-,Ti-,Al-oxide which will prohibit filling and wetting of insert metal. Depth and propagation direction of crack were accorded with centrifugal force and temperature distribution in turbine bucket. Present result will provide basic data for repair bonding process.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.229-234
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• 2001

The thermoacoustic refrigerator bas not only considerable possibility but also commercial usability, because it bas high reliability, lower vibration, no moving part, and can easily be constructed. In this study, the resonance characteristics of the thermoacoustic refrigerator were investigated for better performance, varying length of the resonance tube to 400mm, 500mm, 600mm, 700mm. In order to determine the optimum resonance tube length and the frequency, the $\lambda/4$ thermoacoustic engine and the similar apparatus of Wheatly type refrigerator were constructed. It was used air as a coolant. in the fifth harmonic, it was taken the highest ${\Delta}t$ that was $56.3^{\circ}C$ at 626Hz in 400mm tube with 40mm stack.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.217-222
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• 2001

The thermoacoustic refrigerator has not only considerable possibility but also commercial usability, because it has high reliability, lower vibration, no moving part, and can easily be constructed. In this study, the resonance characteristics of the thermoacoustic refrigerator were investigated for better performance, varying the length of Resonant Tube to 400mm $\sim850mm$. In order to determine the optimum position of stack in the resonance tube and the frequency, the simple $\lambda/2$ thermoacoustic refrigerator was constructed. It was used air as a coolant. in the fifth harmonic, it was taken the highest ${\Delta}t$ that was $52.6^{\circ}C$ at 827Hz in 400mm tube with 40mm stack.

• Coupled systems mechanics
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• v.12 no.2
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• pp.103-125
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• 2023

The present research is focused on the study of plane harmonic waves in a two-dimensional orthotropic magneto-thermoelastic media with fractional order theory of generalized thermoelasticity in the light of two-temperature and rotation due to time harmonic sources. Here, we studied three types of waves namely quasi-longitudinal (QL), quasi-transverse (QTS) and quasi thermal (QT) waves. The variations in the wave properties such as phase velocity, attenuation coefficient and specific loss have been noticed with respect to frequency for the reflected waves. Further the value of amplitude ratios, energy ratios and penetration depth are computed numerically with respect to angle of incidence. The numerical simulated results are presented graphically to show the effect of fractional parameter based on its conductivity (0<α<1 for weak, α=1 for normal, 1<α≤2 for strong conductivity) on all the components.