• 한국세라믹학회지
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• 제28권11호
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• pp.878-884
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• 1991

The mobility and diffusivity in an edge dislocation in an FCC crystal formed by the removal of one half of a (100) plane were evaluated in an applied field by analyzing a vacancy tight binding model using Stark's matrix technique. A model of an edge dislocation in an FCC crystal was constructed for a [100] Burgers vector where vacancy transport along the edge dislocation in an FCC crystal was constructed for a [100] Burgers vector where vacancy transport along the edge of the extrac half plane of ions was considered. The model considered a tight binding approximation of the vacancy to the compressed region of the core and carried the calculation to the limit of an infinite length of dislocation. The diffusivity and the ratio of mobility to diffusivity were found to increase without bounds in the limit where the correlation factor becomes zero. In contrast, as the correlation factor became unity, the diffusivity became zero and the ratio of mobility to diffusivity became unity associated with the uncorrelated limit of 1/kT. This implied that the phenomenon was not unique to the crystal structure but was unique to edge dislocations with vacancy tight binding.

• 대한기계학회논문집B
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• 제26권12호
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• pp.1747-1755
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• 2002

A complete theoretical treatment of the photothermal displacement technique has been performed for thermal diffusivity measurement in semi-infinite solid materials. The influence of the parameters, such as radius and modulation frequency of the heating beam and the thermal diffusivity, was studied. Usually, thermal diffusivity was determined by the deformation angle and phase angle as the relative position between the heating and probe beams. In this study, we proposed the simple analysis method based on the real part of deformation gradient as the relative position between two beams. It is independent in the parameters such as power of heating beam, absorption coefficient, reflectivity, Poisson's ratio, and thermal expansion coefficient.

• 한국지열·수열에너지학회논문집
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• 제7권1호
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• pp.1-9
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• 2011

Storing and transferring heat in soils is governed by the soil thermal properties and these properties are therefore needed in many engineering applications, including horizontal ground heat exchanger for ground-coupled heat pumps. This paper presents the evaluation results of the ground subsurface temperature and apparent thermal diffusivity of soils by using ground temperature data collected at the depths of 0.5 m, 1.0 m, 1.5 m, 3.0 m, and 5.0 m at four sites. The existing correlation assuming that the soil was homogeneous and of constant thermal diffusivity was applied to calculate the subsurface temperature and two analytical equations, amplitude and phase equation, were also used to evaluate the soil apparent thermal diffusivity. Comparison of the estimated and of the measured values of the subsurface temperature has shown that the empirical correlation predicts quite accurately the ground temperature at various depths. Based on the one-dimensional heat conduction equation, the apparent thermal diffusivity can be estimated by the two equations.

• 한국식품과학회지
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• 제20권5호
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• pp.711-717
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• 1988

배추의 염절임중 배추 조직으로의 소금흡수 속도를 측정하고 확산에 관한 수학적인 모델과 computer simulation을 통해서 확산계수를 구하였다. 배추 줄기로의 소금의 침투 및 탈염 될 때의 확산계수는 각각 $1.7{\times}10^{-11}m^2/s$와 $11.6{\times}10^{-11}m^2/s$이었다. Apparent diffusivity는 소금의 농도와 배추의 종류에 커다란 영향을 받지 않으며, 온도의존성은 Arrhenius식으로 나타낼 수 있고 이때의 활성화 에너지는 66 KJ/mol 이었다.

• Journal of Mechanical Science and Technology
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• 제18권10호
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• pp.1712-1721
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• 2004

A method of measuring the thermal diffusivity of semi-infinite solid material at room temperature using photothermal displacement is proposed. In previous works, within the constant thickness of material, the thermal diffusivity was determined by the magnitude and phase of deformation gradient as the relative position between the pump and probe beams. In this study, however, a complete theoretical treatment of the photothermal displacement technique has been performed for thermal diffusivity measurement in semi-infinite solid materials. The influence of parameters, such as, radius and modulation frequency of the pump beam and the thermal diffusivity, was studied. We propose a simple analysis method based on the zero -crossing position of real part of deformation gradient and the minimum position of phase as the relative position between two beams. It is independent of parameters such as power of pump beam, absorption coefficient, reflectivity, Poisson's ratio, and thermal expansion coefficient.

• 대한기계학회논문집B
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• 제27권9호
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• pp.1220-1228
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• 2003

The mirage technique is proved to be powerful in measuring the thermal diffusivity of materials. In particular, its contactless nature makes it suitable for delicate samples and microscale structures. In this study, thermal-wave-coupling method is developed in a general form for both thermally thin and thick samples. In the suggested measuring scheme, the probe beam can be positioned close to the pump beam and the absolute position need not be measured. Therefore the new scheme provides a relatively simple yet effective way to determine the thermal diffusivity of thermally thick samples. Thermal diffusivities of bulk samples like Ni and Al were measured and the characteristics of mirage signal for a thin film were observed by using the mirage experimental setup. The apparent thermal diffusivity was measured by varying such parameters as probe beam height, size of pump beam, power of pump beam, and surface condition of sample. From the practical standpoint, it is shown that the size of the pump beam is the most important factor for accurate thermaldiffusivity measurement. Experiments using thin-film samples show that the thermal diffusivity of a substrate covered with thin film can be measured by photothermal mirage signals.

• 한국건축시공학회지
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• 제11권4호
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• pp.379-386
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• 2011

Durability of concrete is an important issue, and one of the most critical aspects affecting durability is chloride diffusivity. Factors such as water.cement ratio, degree of hydration, volume of the aggregates and their particle size distribution have a significant effect on chloride diffusivity in concrete. The use of polypropylene fibers(particularly very fine and well dispersed micro fibers) or mineral additives has been shown to cause a reduction in concrete's permeability. The main objective of this study is to evaluate the manner in which the inclusion of fiber(in terms of volume and size) and blast furnace slag(BFS) (in terms of volume replacement of cement) influence the chloride diffusivity in concrete by applying 3D computer modeling for the composite structure and performing a simulation of the chloride penetration. The modeled parameters, i.e. chloride diffusivity in concrete, are compared to the experimental data obtained in a parallel chloride migration test experiment with the same concrete mixtures. A good agreement of the same order is found between multi.scale microstructure model, and through this chloride diffusivity in concrete was predicted with results similar to those experimentally measured.

• 항공우주기술
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• 제10권1호
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• pp.39-44
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• 2011

다공성 소재의 열 확산도 측정 시스템을 개발하였다. 열확산도를 측정하는 다양한 시스템이 있지만 다공성 소재의 열확산도를 측정하는 것은 기존의 시스템으로는 어렵다. 본 논문에서는 주기가열법을 이용한 열확산도 측정시스템 및 장비의 검증에 대하여 정리하였다. 주기가열법을 검증하기 위해서 사용한 표준시편은 세라믹 소재를 사용하였다. 그 결과 표준값과 측정값이 일치함을 보였다. 다공성 소재 적용을 위하여 검증한 시편은 폴리스티렌 폼이었다. 진공에서 열확산도 값도 측정하였는데, 진공에서 열확산도는 대기조건과 비교하여 63% 감소함을 보였다. 두 결과 모두 측정값과 표준값은 10% 오차 범위 이내에 있었다.

• 한국재료학회지
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• 제30권9호
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• pp.474-479
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• 2020

The effect of precipitation and dissolution of Si on the thermal diffusivity in the Al-Si alloy system is reported in this study and solution heat treatment followed by aging treatment is carried out to determine the effects of heat treatment on the thermal characteristics. The solution treatment is performed at 535 ℃ for 4 and 10 h and then the specimens are cooled by rapid quenching. The samples are aged at 300 ℃ for 4 h to precipitate Si solute. The addition of 9 wt% silicon contents makes the thermal diffusivity decrease from 78 to 74 mm/s² in the cases of solid solution treated and quenched samples. After quenching and aging, the Si solute precipitates on the Al matrix and increases the thermal diffusivity compared with that after the quenched state. In particular, the increase of the thermal diffusivity is equal to 10 mm/s² without relation to the Si contents in the Al-Si alloy, which seems to corresponded to solute amount of Si 1 wt% in the Al matrix.

• 한국재료학회지
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• 제31권11호
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• pp.642-648
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• 2021

The precipitation effect of Al-6%Si-0.4%Mg-0.9%Cu-(Ti) alloy (in wt.%) after various heat treatments was studied using a laser flash device (LFA) and differential scanning calorimetry (DSC). Solid solution treatment was performed at 535 ℃ for 6 h, followed by water cooling, and samples were artificially aged in air at 180 ℃ and 220 ℃ for 5 h. The titanium-free alloy Al-6%Si-0.4%Mg-0.9%Cu showed higher thermal diffusivity than did the Al-6%Si-0.4%Mg-0.9%Cu-0.2%Ti alloy over the entire temperature range. In the temperature ranges below 200 ℃ and above 300 ℃, the value of thermal diffusivity decreased with increasing temperature. As the sample temperature increased between 200 ℃ and 400 ℃, phase precipitation occurred. From the results of DSC analysis, the temperature dependence of the change in thermal diffusivity in the temperature range between 200 ℃ and 400 ℃ was strongly influenced by the precipitation of θ'-Al₂Cu, β'-Mg₂Si, and Si phases. The most important factor in the temperature dependence of thermal diffusivity was Si precipitation.