• 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.

• 한국전산유체공학회지
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• 제10권3호
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• pp.36-42
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• 2005

The present study numerically investigates the natural convection heat transfer in a 2-D square cavity containing a centered heat conducting body. Special emphasis is given to the influences of the Rayleigh number, the dimensionless conducting body size, and the ratio of the thermal diffusivity of the body to that of the fluid on the natural convection heat transfer in overall concerned region. The analysis reveals that the fluid flow and heat transfer processes are governed by all of them. Results for isotherms, vector plots and wall Nusselt numbers are reported for Pr = 0.71 and relatively wide ranges of the other parameters. Heat transfer across the cavity, in comparison to that in the absence of a body, are enhanced (reduced) in general by a body with a thermal diffusivity ratio less (greater) than unity. It is also found that the heat transfer attains a minimum as the body size is increased with a thermal diffusivity ratio greater than unity.

• 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.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 춘계 학술대회논문집
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• pp.79-84
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• 2005

The numerical solutions are examined on the effect of a centered heat conducting body on natural convection in a 2-D square cavity. The influences of the Rayleigh number, the dimensionless conducting body size, and the ratio of the thermal diffusivity of the body to that of the fluid have been investigated on the natural convection heat transfer in overall concerned region. The analysis reveals that the fluid flow and heat transfer processes are governed by all of them. Results for isotherms, vector plots and wall Nusselt numbers are reported for Pr = 0.71 and relatively wide ranges of the other parameters. Heat transfer across the cavity, in comparison to that in the absence of a body, are enhanced (reduced) in general by a body with a thermal diffusivity ratio less (greater) than unity. The heat transfer are also found to attain a minimum as the body size is increased.

• 한국자동차공학회논문집
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• 제5권4호
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• pp.219-224
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• 1997

A transient short-hot-wire technique has been presented for simultaneous measurements of the thermal conductivity and diffusivity of fluids under the microgravity condition. Two-dimensional heat conduction equations for concentric cylinders with various radius ration and length-diameter ratio have been solved numerically by taking account of the heat capacity of the inner cylinder. A unique relation between the non-dimensional temperature of inner cylinder and Fourier number is obtained for a wide range of thermal properties of the fluids, because the relation if found to be almost independent of these properties. Then the characteristic could be utilized as a masterplot to evaluate both the thermal conductivity and diffusivity. In principle, this method is proved to have an error within 1% for both of these properties.

• 대한기계학회논문집
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• 제14권1호
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• pp.214-224
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• 1990

본 연구에서는 현 저자의 이전의 연구를 확장하여 균일한 열유속을 갖는 2상 기체-고체입자 위 방정식에서 축 방향의 열전달은 반경 방향의 열전달보다 작아 무시 하였으며, 복사 열전달은 기체와 입자 사이의 온도 차이가 적어 무시하였다. 방정식 중 $F_{px}$ 와 $F_{pr}$ 은 2상 사이의 상호작용에 의한 단위부피당 축방향과 반경방향 의 저항력이며, 수직관의 열전달 특성을 부하도와 상대 입자 크기 $d_{p}$/D를 변화시 켜 가면서 조사하는 것이다.다.

• 접착 및 계면
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• 제9권3호
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• pp.7-13
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• 2008

열전도도가 유사한 입자형 필러인 silicon carbide (SiC)와 섬유형 필러인 carbon fiber (CF)를 polyetheretherketone (PEEK) 고분자에 첨가하여 복합재료의 열확산도에 미치는 영향을 연구하였다. 전자현미경을 통해 얻은 단면사진으로부터 SiC와 CF가 PEEK 매트릭스 안에 균일하게 분산되어 있고 필러들이 부분적으로 서로 네트워크를 형성한 것을 관찰하였다. 레이저 섬광법을 이용하여 상온에서 $200^{\circ}C$까지 PEEK/SiC와 PEEK/CF 복합재료의 열확산도를 측정하였으며, 열확산도는 온도가 상승함에 따라 PEEK-필러와 필러-필러 계면에서의 포논산란 증가에 의하여 감소하였다. 필러함량이 증가함에 따라 복합재료의 열확산도가 증가하였으며, 2상계에 대하여 유도된 Maxwell 및 Nielson 예측식을 실험값과 비교함으로써 매트릭스 내의 필러 분포, 방향성, 종횡비 및 필러간의 상호작용 등을 유추할 수 있었다. Nielson 예측식은 PEEK/SiC 복합재료에 대하여 열전도도를 잘 예측하였다. 입자형 필러인 SiC에 비하여 섬유형 필러인 탄소섬유가 동일한 함량에서 열확산에 기여하는 필러 네트워크를 효과적으로 형성하여 높은 열확산도를 가지는 것으로 추정된다.

• 한국추진공학회지
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• 제3권1호
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• pp.78-85
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• 1999

복기 추진제인 N-5 추진제에 4종의 금속선(Ag, Cu, Al, Ni-Cr선)을 삽입하여 연소 특성을 고찰하여 보았다. 금속선이 삽입된 복기 추진제의 연소속도 증가비($r_w$/$r_sb$)는 Ag선 > Cu선 > Al선 > Ni-Cr선의 순으로서 금속선의 열확산 계수의 크기 순과 일치하였다. 금속선을 삽입한 N-5추진제의 $r_w$/$r_sb$는 단열 불꽃 온도와 구조의 차이에 의하여 혼합형 추진제보다 작게 나타났다. 복기 추진제에 열확산 계수가 비교적 큰 Ag, Cu, Al선을 삽입한 경우, 금속선이 삽입되지 않은 추진제에서 나타난 plateau와 mesa 연소 특성이 사라진 반면 열확산 계수가 작은 Ni-Cr선을 삽입한 경우에서는 plateau와 mesa 연소 특성이 그대로 존재했다.

• 대한기계학회논문집B
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• 제29권10호
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• pp.1075-1082
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• 2005

The characteristics of longitudinal dispersion enhancement by the flow oscillation are numerically studied according to various groove geometries in a 2-D channel in the present study. The length of expanded section l$_{1}$/h$_{1}$ is varied from 0 to 8.75. The oscillating flow condition is given at both side ends, i.e., u = Asin ($2{\pi}ft$) The non-dimensional temperatures at both side ends are set to zero. The bottom and top walls are adiabatic. The local heat sources are located at the middle of the groove wall. In order to solve the governing equations, the SIMPIER algorithm is employed. The present results indicate that maximum longitudinal thermal dispersion can be achieved when the area ratio of the expanded section to the contracted section in the grooved channel becomes 1.

• 한국재료학회지
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• 제32권10호
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• pp.429-434
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• 2022

There is ongoing research to develop lithium ion batteries as sustainable energy sources. Because of safety problems, solid state batteries, where electrolytes are replaced with solids, are attracting attention. Sulfide electrolytes, with a high ion conductivity of 10^-3 S/cm or more, have the highest potential performance, but the price of the main materials is high. This study investigated lithium hydride materials, which offer economic advantages and low density. To analyze the change in ion conductivity in polymer electrolyte composites, PVDF, a representative polymer substance was used at a certain mass ratio. XRD, SEM, and BET were performed for metallurgical analyses of the materials, and ion conductivity was calculated through the EIS method. In addition, thermal conductivity was measured to analyze thermal stability, which is a major parameter of lithium ion batteries. As a result, the ion conductivity of LiH was found to be 10^-6 S/cm, and the ion conductivity further decreased as the PVDF ratio increased when the composite was formed.