• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.10
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• pp.453-459
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• 2014

This paper presents an analysis on the initial ignoring time of SCW type GHX using Mean Square Error method. Line source method is a useful method for estimating the ground thermal conductivity for the vertical type and SCW type GHX in Korea. The line source method for ground thermal conductivity of geothermal in-site test is the basis of linear approximation between the temperature of a borehole and logarithmic time in a GHX. To apply the line source method to the estimation of SCW type GHX, it is necessary to ignore the initial time of data at the stage of a linear approximation. This paper proposed a new initial ignoring time of SCW type GHX among various initial ignoring time at the time for reaching MSE of $0.02^{\circ}C^2$.

• Polymer(Korea)
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• v.38 no.6
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• pp.782-786
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• 2014

Various kinds of thermal conductive ceramic/polymer composites (aluminum nitride, aluminum oxide, boron nitride, and silicon carbide/epoxy) were prepared by a casting method and their optical images were observed by FE-SEM. Among these, SiC/epoxy composite shows inhomogeneous dispersion features of SiC and air voids in the epoxy matrix layer, resulting in undesirable thermal conductive properties. To enhance the thermal conductivities of SiC/epoxy composites, the epoxy wetting method which can directly infiltrate the epoxy droplet onto filtrated SiC cake was employed to fabricate the homogeneously dispersed SiC/epoxy composite for ideal thermal conductive behavior, with maximum thermal conductivity of 3.85W/mK at 70 wt% of SiC filler contents.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.12
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• pp.957-962
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• 2014

We present a method to quantitatively measure the thermal conductivity of one-dimensional nanostructures by utilizing scanning thermal wave microscopy (STWM) at a nanoscale spatial resolution. In this paper, we explain the principle for measuring the thermal diffusivity of one-dimensional nanostructures using STWM and the theoretical analysis procedure for quantifying the thermal diffusivity. The SWTM measurement method obtains the thermal conductivity by measuring the thermal diffusivity, which has only a phase lag relative to the distance corresponding to the transferred thermal wave. It is not affected by the thermal contact resistances between the heat source and nanostructure and between the nanostructure and probe. Thus, the heat flux applied to the nanostructure is accurately obtained. The proposed method provides a very simple and quantitative measurement relative to conventional measurement techniques.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.13 no.2
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• pp.99-112
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• 2015

In this study, laboratory test equipment was designed and installed to evaluate the thermal behavior of bentonite, which is used as a buffer in high-level waste disposal systems. The thermal analysis was conducted to verify the test results using ABAQUS, a finite element analysis code. In view of the seasonal changes seen during the test, the thermal behavior of bentonite with a temperature of outside air was evaluated. Of the cases examined, the results of the analysis model using stainless steel (Case 3) approximates to the test results, showing an error of about 1℃. The results of the thermal analysis into seasonal temperature distributions are consistent with trends seen in lab-test results. These analyses show that the effects of the thermal conductivity of the material surrounding the buffer and outside air temperature, are very important factors in the thermal behavior of bentonite. In the future, it is expected that a moisture saturation test of a bentonite buffer containing a heat source will be carried out. Therefore, the development of a numerical analysis model is required for the prediction and verification of the laboratory test results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.4
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• pp.367-375
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• 2013

In this study, the characteristics of the heat transfer coefficient and pressure drop were numerically analyzed according to the axis ratio (AR), pitch, location of vortex generator, and bump phase of the tube surface about an elliptical fin-tube heat exchanger. The boundary condition for CFD analysis was decided as a tube surface temperature of 348 K and inlet air velocity of 1-5 m/s. RSM 7th turbulent model was chosen as the numerical analysis for the sensitivity level. The analysis results indicated that the AR and transverse pitch decreased whereas the heat transfer coefficient increased. On the other hand, there was little difference in the longitudinal pitch. Furthermore, the heat transfer rate was more favorable when the vortex generator was located in front of the tube. Also, the bump phase of the tube surface indicated that the pressure drop and heat transfer were more favorable with the circle type than with the serrated type.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2013.04a
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• pp.18-18
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• 2013

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.5
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• pp.561-569
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• 1999

The effects of longitudinal heat conduction on the performance of heat transfer surfaces are investigated by using a single-blow method. In the transient testing method for determining the heat transfer characteristics, exponential inlet temperature variations are made by using screen-mesh heater with small time constant and low frontal velocities of the test section, and the experimentally determined inlet temperature profile is used as the inlet fluid temperature condition. The effects of longitudinal heat conduction are negligible only if $\gamma^\act<0.05\;and \;N_{tu}\le3$ and should be considered if $N_{tu}\le3$ The test results ate compared with the existing theoretical and experimental data and the validity of this technique is confirmed by the good agreement.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.2
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• pp.265-279
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• 1986

Ra=$10^{6}$, Pr=5에서 관열전도율과 두께가 변화할 때의 단일수평관에서의 자연대류 열전달에 관하여 유한차분법을 이용하여 해석적으로 연구하였다. .delta.$_{w}$ /d$_{o}$ =0.1에서 관열전도율이 높을수록 높은 온도와 높은 국소 누셀트 수를 나타 내며, .theta.=20。에서의 원주방향속도는 (r-r$_{o}$ )=0.08에서 최대가 되며 반경방향속 도는 (r-r$_{o}$ )=0.14에서 최대가 된다. 관외벽온도는 관 두께가 증가함에 따라 거의 유사하게 감소한다. $K_{w}$ /K$_{f}$ =75에서 각도변위가 증가함게 따라 국소 누셀트수는 현저히 증가하나 관 두께가 증가함에 따라서는 감소한다. .delta.$_{w}$ / d$_{o}$ =0.1에서 평균 누셀트수와 평균 온도는 무차원 열전도율이 증가함에 따라 $K_{w}$ /K$_{f}$ ＞15에서는 평균 누셀트 수는 서서히 증가하고 평균 온도는 거의 같 은 값을 가지며 지수함수로 표시할 수 있었다. $K_{w}$ /K$_{f}$ =75,50에서 평균 누 셀트수와 온도는 무차원 관 두께가 증가함에 따라 거의 직선적으로 감소되며 선형 함 수로 나타낼 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.1 no.3
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• pp.156-163
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• 1977

길이방향의 열전도효과가 비교적 큰유체- 고체 열교환계내에 일정한 조ㅍ은 온도를 가진 유체가 유입될 때 이에 따른 비정상 온도분포가 해석되었다. 이러한 계를 기술하는 연립편미분 방정식의 수치해가 유한차분법에 의해 구해졌으며, 열전도가 무시된 경우에 대한 해석적 해를 구하여 위의 결과를 검증하였다. 한편 이상화된 모델에 대한 실험을 행하고 이 결과를 앞서 구한 수치해와 비교 검토하였다. 여기서 구해진 온도분포를 이용하여 축열효율${\eta}_A$및 ${\eta}_B$를 ${\eta}_A$는 시간 t에서의 축열량과 정상상태에 도달했을 때의 축열량의 비로 , 그리고 ${\eta}_B$는 시간 t 동안의 축열된 양과 공급된 열량의 비고 정의하여 온도분포와 효율들에 애하여 시간변수 .tau., 위치변수 .xi.와 무차원 열확산율 .betha.가 미치는 영향을 조사하였다. 이에 따르면 온도는 .betha. 가 적어짐에 따라 점점 가파르게 분포되고 한편 ${\eta}_A$는 .tau.가 점점 커지거나, .xi.가 작아질수록 좋아지는 것을 알 수 있다. 또한 ${\eta}_B$는${\eta}_A$와는 정반대의 경향을 보여주어 축열계의 최적상태가 존재함을 알 수 있다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.645-652
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• 2000

A method for shape design sensitivity analysis is proposed utilizing commercial software ANSYS for thermal conduction problems. While the sensitivity formula is derived analytically by introduing adjoint variable concept, sensitivity calculation in practice as well as the primal and adjoint solution of thermal conduction is performed using the ANSYS very easily. Since the formula always takes boundary integral form, sensitivity evaluation in ANSYS requires a little more addition of post-processing routine which involves evaluation of boundary variable from the obtained solution. Though the BEM has been used as a better tool for this purpose, the present study shows it can also be calculated using any kind of analysis code such as ANSYS since the formula is based on analytic nature. Therefore the present study provides a new and efficient way of optimization which was not possible before using commercial software. The usefulness of the method is illustrated via a weight minimization problem of thermal diffuser.