• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제9권2호
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• pp.45-53
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• 2005

This paper investigates the influence of thermal conductivity and variable viscosity on the problem of micropolar fluid in the presence of suction or injection. The fluid viscosity is assumed to vary as an exponential function of temperature and the thermal conductivity is assumed to vary as a linear function of temperature. The governing fundamental equations are approximated by a system of nonlinear ordinary differential equations and are solved numerically by using shooting method. Numerical results are presented for the distribution of velocity, microrotation and temperature profiles within the boundary layer. Results for the details of the velocity, angular velocity and temperature fields as well as the friction coefficient, couple stress and heat transfer rate have been presented.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 봄 학술발표회 논문집
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• pp.548-555
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• 2000

It was investigated whether the waste polyethylene chips can be recycled as construction materials in geotechnical engineering field. The standard Proctor test, the hydraulic conductivity test, the large box direct shear test, the thermal conductivity test, the frost heaving test and the time domain reflectometry test were performed on weathered granite soil mixed with variable amount of the waste polyethylene chips. The experimental results showed that the hydraulic conductivity and the shear strength of weathered granite soil increase with increasing the amount of the waste polyethylene chips. On the other hand, the thermal conductivity, the amount of frost heaving and the unfrozen water contents of weathered granite soil decrease with increasing the amount of the waste polyethylene chips.

• Structural Engineering and Mechanics
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• 제34권3호
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• pp.285-300
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• 2010

The two-dimensional deformation of a homogeneous, isotropic thermoelastic half-space with voids with variable modulus of elasticity and thermal conductivity subjected to thermomechanical boundary conditions has been investigated. The formulation is applied to the coupled theory(CT) as well as generalized theories: Lord and Shulman theory with one relaxation time(LS), Green and Lindsay theory with two relaxation times(GL) Chandrasekharaiah and Tzou theory with dual phase lag(C-T) of thermoelasticity. The Laplace and Fourier transforms techniques are used to solve the problem. As an application, concentrated/uniformly distributed mechanical or thermal sources have been considered to illustrate the utility of the approach. The integral transforms have been inverted by using a numerical inversion technique to obtain the components of displacement, stress, changes in volume fraction field and temperature distribution in the physical domain. The effect of dependence of modulus of elasticity on the components of stress, changes in volume fraction field and temperature distribution are illustrated graphically for a specific model. Different special cases are also deduced.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.134-135
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• 2005

To improve mean-life and reliability of power cable, we have investigated volume resistivity and thermal conductivity showed by changing the content of acetylene black which is the component parts of semiconductive shield in underground power transmission cable. The sheets were primarily kneaded in their pellet form material samples for 5 minutes on rollers ranging between 70[$^{\circ}C$] and 100[$^{\circ}C$]. Then they were produced as sheets after pressing for 20 minutes at 180[$^{\circ}C$] with a pressure of 200[kg/cm]. The content of conductive acetylene black was the variable, and their contents were 20, 30 and 40[wt%], respectively. Volume resistivity of specimens was measured by volume resistivity meter after 10 minutes in the preheated oven of both $25\pm1[^{\circ}C]$ and $90\pm1[^{\circ}C]$. Thermal conductivity was measured by Nano Flash Diffusivity. The measurement temperatures of thermal conductivity using Nano Flash Diffusivity were both 25[$^{\circ}C$] and 55[$^{\circ}C$]. From these experimental results, volume resistivity was high according to an increase of the content of acetylene black. And thermal conductivity was increased to an increase of the content of acetylene black. And thermal conductivity were increased by heating rate because volume of materials was expanded according to rise in temperature.

• 항공우주시스템공학회지
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• 제13권2호
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• pp.66-72
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• 2019

SAR(Synthetic Aperture Radar) 관측위성과 같이 고 발열 임무장비가 다수 적용되는 경우 전장품의 발열을 효과적으로 우주공간으로 방출하기 위한 방열판의 적용이 요구된다. 그러나 위성의 식 구간에서 임무장비의 비작동 시, 방열판을 통해 지속적인 방열이 이루어짐에 따라 장비의 최소허용 온도유지를 위한 히터 적용이 불가피하게 된다. 본 연구에서는 기존 방열판에 비해 보다 효율적인 열제어를 위하여 높은 전도율의 액체금속을 이용한 우주용 가변 전도율 방열판을 제안하였다. 제안된 방열판은 탑재장비의 온도조건에 따라 두 개의 저장소 사이에서 기계식 펌프로 액체금속을 이동함으로서 열전도 특성을 가변하는 원리이다. 따라서 저온 조건에서는 방열판으로의 열전도를 차단하여 임무장비에 대한 히터 전력소모를 최소화하고, 반대로 고온 조건에서는 기존 방열판과 같이 효과적인 방열이 가능하도록 한다. 본 연구에서는 제안한 가변 전도율 방열판의 실현 가능성 입증을 위한 열해석을 실시하여 기존의 전도율이 고정된 방열판과 열적 성능을 비교 분석하였다.

• Steel and Composite Structures
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• 제51권2호
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• pp.139-151
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• 2024

In this research, a semi-analytical solution is presented for computing mechanical displacements and thermal stresses in rotating thick cylindrical pressure vessels made of functionally graded material (FGM). The modulus of elasticity, linear thermal expansion coefficient, and density of the cylinder are assumed to change along the axial direction as a power-law function. It is also assumed that Poisson's ratio and thermal conductivity are constant. This cylinder was subjected to non-uniform internal pressure and thermal loading. Thermal loading varies in two directions. The governing equations are derived by the first-order shear deformation theory (FSDT). Using the multilayer method, a functionally graded (FG) cylinder with variable thickness is divided into n homogenous disks, and n sets of differential equations are obtained. Applying the boundary conditions and continuity conditions between the layers, the solution of this set of equations is obtained. To the best of the researchers' knowledge, in the literature, there is no study carried out bi-directional thermoelastic analysis of clamped-clamped rotating FGM thick-walled cylindrical pressure vessels under variable pressure in the longitudinal direction.

• 한국주조공학회지
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• 제32권6호
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• pp.276-283
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• 2012

This study presents the results on the changes of crucible thermal conductivity and inflow of Ar, and constructed the mathematical model about heat transfer into furnace. As process variables, simulation model was designated thermal conductivity of crucible to $0.5W{\cdot}m^{-1}{\cdot}K^{-1}$, $1W{\cdot}m^{-1}{\cdot}K^{-1}$, $2W{\cdot}m^{-1}{\cdot}K^{-1}$, $4W{\cdot}m^{-1}{\cdot}K^{-1}$, and inflow rate of Ar to 15 L/min, 30 L/min, 60 L/min. Initial condition and boundary condition were set respectively in two terms of process. Each initial conditions were set up by the preceding simulation of heat and fluid flow. The primary goal is the application of unidirectional growth of Si ingot using the result. In the result of the change of heat conductivity of crucible, the higher thermal conductivity of crucible shows the shorter solidification time and the bigger temperature difference. And the flow patterns are changed with the inflow rate of Ar. Finally, we found that the lower crucible's thermal conductivity, the better crucible is at polycrystalline Si ingot growth. But in case of Ar inflow, it is hard to say about good condition. This data will be evaluated as useful reference used in allied study or process variable control of production facilities.

• 한국전산구조공학회논문집
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• 제23권6호
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• pp.683-691
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• 2010

In this paper, using an adjoint variable method, we develop a design sensitivity analysis(DSA) method applicable to heat conduction problems in steady state. Also, a topology design optimization method is developed using the developed DSA method. Design sensitivity expressions with respect to the thermal conductivity are derived. Since the already factorized system matrix is utilized to obtain the adjoint solution, the cost for the sensitivity computation is trivial. For the topology design optimization, the design variables are parameterized into normalized bulk material densities. The objective function and constraint are the thermal compliance of structures and allowable material volume respectively. Through several numerical examples, the developed DSA method is verified to yield very accurate sensitivity results compared with finite difference ones, requiring less than 0.25% of CPU time for the finite differencing. Also, the topology optimization yields physical meaningful results.

• 한국전기화학회:학술대회논문집
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• 한국전기화학회 2001년도 연료전지심포지움 2001논문집
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• pp.189-192
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• 2001

In order to prepare the proton-conducting membrane with lower cost and higher ionic conductivity than commercialized one, the concept of incorporating the nitrogen acid to polymer backbone, is proposed. The synthesis, thermal, and temperature-variable impedance/electrical conductivity studies of poly (p-tolunesulfonylamido acrylate) are reported. This polymer can be prepared by reacting poly (acryloyl chloride) with ptolunesulfonamide and cast into homogeneous membranes. Thermogravimetric analysis (TGA) shows that the polymer is thermally stable up to about $200^{\circ}C$ and Differential scanning calorimetry (DSC) illustrates that the glass transition occur at around $67^{\circ}C$. The ionic conductivity measured by dielectric spectroscopy is in the range of $10^{-5}\;S/cm$ in dry atmosphere that it can be a candidate for the membrane of PEMFC or DMFC.

• 한국지반공학회논문집
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• 제34권1호
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• pp.17-24
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• 2018

심층 처분시설에서 완충재는 지하수의 유입을 최소화하며, 역학적인 충격을 흡수하는 중요한 역할을 한다. 사용후 핵연료로부터 발생하는 붕괴열은 완충재의 온도를 변화시켜 역학적 성능에 큰 영향을 미치기 때문에 완충재 온도변화에 대한 정확한 예측이 필요하다. 이러한 온도 변화는 완충재의 열물성인 열전도도, 밀도, 비열에 영향을 받으며, 이에 대한 영향이 심층 처분시설의 열 해석에 고려되어야 한다. 특히 이들 열물성은 벤토나이트 완충재의 밀도와 함수비에 따라 변화하기 때문에 이에 대한 영향이 해석에 포함되어야한다. 따라서 본 연구에서는 완충재의 밀도와 함수비 변화 영향을 고려할 수 있는 유한요소법 기반의 열 해석 수치모델을 설정하였다. 또한 수치모델을 바탕으로 매개 변수 연구를 수행하여 각각의 열물성이 완충재의 온도 변화에 미치는 영향에 대해 살펴보았다.