• 대한기계학회논문집B
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• 제25권1호
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• pp.47-53
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• 2001

As the technology has developed and new materials have been produced, it is important to measure the thermal diffusivity of material and to predict the heat transfer in the solid subject to thermal processes. This measurement can be done in a non-contact way using photothermal displacenent spectroscopy. In this study, photothermal displacement method was used to measure the thermal diffusivity quantitatively. The specimens used in this study were the pure materials. The Ar-ion laser was used as an energy source and the periodical deformation induced by this pump laser was detected by the He-Ne laser. The magnitude and the phase angle of deformation gradient were measured. The thermal diffusivity was obtained by analyzing the phase angle of deformation gradient. As the result, comparing with the literature value, the thermal diffusivities of materials measured were showed about 2% error.

• Nuclear Engineering and Technology
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• 제49권3호
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• pp.459-465
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• 2017

The goal of this study is to evaluate the effective thermal conductivity and diffusivity of containment walls as heat sinks or passive cooling systems during nuclear power plant (NPP) accidents. Containment walls consist of steel reinforced concrete, steel liners, and tendons, and provide the main thermal resistance of the heat sinks, which varies with the volume fraction and geometric alignment of the rebar and tendons, as well as the temperature and chemical composition. The target geometry for the containment walls of this work is the standard Korean NPP OPR1000. Sample tests and numerical simulations are conducted to verify the correlations for models with different densities of concrete, volume fractions, and alignments of steel. Estimation of the effective thermal conductivity and diffusivity of the containment wall models is proposed. The Maxwell model and modified Rayleigh volume fraction model employed in the present work predict the experiment and finite volume method (FVM) results well. The effective thermal conductivity and diffusivity of the containment walls are summarized as functions of density, temperature, and the volume fraction of steel for the analysis of the NPP accidents.

• 대한기계학회논문집
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• 제7권3호
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• pp.319-327
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• 1983

The thermal diffusivity one of the series of standard pieces for spark test are determined by the flash method. The standard pieces are composed with carbon steels, structural carbon steels, alloy steels and high speed tool steels. In order to compute the thermal conductivity of the standard pieces, their specific heats are measured by a differential scanning calorimeter. The thermal conductivities are calculated from the data of specific heat, density and thermal diffusivity. To increase the accuracy of data for the thermal diffusivity by data reduction excursion method in the flash method, the governing heat diffusion equation, which is closely described experimental conditions with the finite pulse and the heat loss from the sample surfaces, is solved. In this analysis an integral transform is used.

• Journal of Biosystems Engineering
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• 제4권2호
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• pp.53-63
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• 1979

The knowlege of thermal properties of rough rice has become of greate importance to the analysis of heat and mass transfer phenomenon in rice drying and storage process. Some information is available on the thermal properties of rough rice in foreign countries but is not available for these properties in Korea. A fundamental study was made to determine the thermal conductivity and thermal diffusivity of rough rice with line source method and to select current and resistance suitable for these properties from investigating the effect of current and resistance of heating wire on the temperature rise. The result of this study may be summarized as follows ; 1. Even through the power per unit length of heating wires is about the same, the tendency of temperature rise showed a little difference among them , and the suitable range of it for thermal properties was found to be 3.56-5.37w/m. 2. the most desirable resistance and current of heating wire was 18.40 ohm/m, 0.44 amperes among three kinds of heating wires and currents, respectively. because it took 13 minutes or so for the heating wire to reach equilibrium temperature. 3. The thermal conductivity of rough rice was 0.120-0.130 w/m$ ^\circ C$. and thermal diffusivity of it was $5.8210 $\times10^{-8} -9.7529 $\times10^{-8} m^2 /s.$ 4.The thermal conductivity showed a little difference in variation with resistance of heating wire but the variation of current of heating wire at the same resistance did not affect the thermal conductivity , and the thermal diffusivity was not affected by the variation of resistance and current.

• 대한기계학회논문집B
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• 제26권2호
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• pp.302-309
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• 2002

A new method of measuring the thermal diffusivity of solid material at room temperature using photothermal displacement is proposed. The influence of the parameters, such as radius and modulation frequency of the pump beam and the sample thickness, was studied. In previous works, thermal diffusivity was determined by the deformation angle and phase angle as the relative position between the heating and probe beams. In this study, however, we proposed the new analysis method based on the real part of deformation angle as the relative position between two beams. From the zero-crossing position of real part of deformation angle with respect to the pump beam, the thermal diffusivity of the materials can be obtained. The experimental values for different samples obtained by applying the new method are in good agreement with the literature values.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.132-137
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• 2000

A complete theoretical treatment of the photothermal displacement technique has been performed for thermal diffusivity measurement in solid materials. The influence of parameters - radius and modulation frequency of pump beam and thickness of material - on the phase lag was studied. The phase decreases up to a certain position, then starts to increase and does have an asymptotic value. The position, where phase has the minimum value, is a function of thermal diffusion length thickness of sample, and radius of pump beam. A new method based on minimum phase lag is described to determine the thermal diffusivity of solid material.

• 접착 및 계면
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• 제15권4호
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• pp.169-173
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• 2014

크기가 다른 2가지 SiC 필러를 Nylon 66에 충전하여 용융혼련 시켜 복합재료를 제조하고 필러 크기가 열확산도에 미치는 영향을 고찰하였다. 필러를 충전하지 않은 경우에 비하여 60 vol%의 SiC 필러를 함유한 경우에 복합재료의 열확산도가 10배 이상 증가함을 확인하였고, SiC 필러의 평균크기가 $24{\mu}m$인 고분자복합재료의 열확산도가 $2.2{\times}10^{-2}cm^2/sec$였으나 필러크기가 76{\mu}m$인 경우에는 $1.75{\times}10^{-2}cm^2/sec$로 20% 감소하였다. 필러의 크기가 $24{\mu}m$인 경우에 열전도성 필러와 Nylon 66 매트릭스의 계면 접촉과 필러와 필러 사이의 접촉을 용이하게 하여 포논이 효과적으로 전달되는 것으로 보인다. Nylon 66보다 상대적으로 강직한 구조와 높은 가공온도를 가지는 Nylon 46를 매트릭스로 사용한 Nylon 46/SiC 400 (60 vol%) 복합재료의 열확산도는 $1.61{\times}10^{-2}cm^2/sec$였다.

• 설비공학논문집
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• 제10권6호
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• pp.795-802
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• 1998

For measuring the thermal diffusivity by laser flash method, raw data have to be calibrated using temperature data. We have developed in-process calibration method and polynomial calibration in which thermal diffusivity can be calibrated during measuring, This method is different from existing temperature pre-process calibration method and exponential calibration having various source of error. Using this new calibration method, measurement accuracy was improved about 1∼2% compare to the value by the existing method. We also studied more accurate fitting curve as in Figure 4 was shown the result of measuring output characteristics of IR radiometer with temperature. As illustrated in data, in-process calibration method and polynomial calibration equation is proper than pre-process calibration method and exponential calibration.

• 대한기계학회논문집
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• 제8권5호
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• pp.462-468
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• 1984

본 연구에서는 구리합금을 냉간 압연하여 이방성 재료를 만들었을 경우 재료 의 압연율과 열유동 방향의 변화에 따른 열확산 계수의 변화를 섬광법으로 측정하여 분석 하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.138-143
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• 2000

A new method of measuring the thermal diffusivity of solid material at room temperature with photothermal displacement method is proposed. The influence of the parameters on phase lag was studied. From the minimum position of phase of measured deflection with respect to the pump beam the thermal diffusivity of the materials can be obtained. The minimum position of phase is determined using multiparameter least-square regression fitting. The experimental values for different samples obtained by applying new method are in good agreement with the literature values.