• 대한기계학회논문집B
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• 제23권1호
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• pp.33-42
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• 1999

The effects of wan thermal boundary condition were investigated for a uniform wall temperature, a uniform wall heat flux, and for coupled heat conduction In the channel wall with transverse rectangular ribs. Numerical investigations for steady laminar flow show behavior similar to that observed experimentally in the separated flow region for flow over a cylinder. Conjugate heat transfer with a low solid-fluid thermal conductivity ratio does not lead to the same results as for the uniform heat flux boundary condition, and heat transfer reversal is found on the back sides of the ribs.

• 전기전자학회논문지
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• 제13권3호
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• pp.55-61
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• 2009

본 논문에서는 정열계 해석을 위해 유한요소법(F.E.M)을 이용한 열전달 해석 기법에 대하여 다루고 있다. 특히, 열전달의 주요 쟁점인 혼합 경계조건을 띄는 대류 경계조건을 자계 문제와 비교하여 갤러킨법(Galerkin Method)으로 정식화하였다. 그리고 해의 신뢰성을 확보하기 위해 자계 해석을 통해 열원이 되는 손실을 구한 후, 반복적 알고리즘을 통해 에너지 평형 방정식을 만족하는 열전달 계수를 산정하여 열전달 문제를 고려하는 자계-열계 결합 해석을 하였다. 마지막으로, 측정치와 비교하여 제안된 방법의 효용성을 증명하였다.

• 대한기계학회논문집B
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• 제24권12호
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• pp.1635-1643
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• 2000

The present work investigates a heat transfer phenomenon at the interface between a porous medium and an impermeable wall. In an effort to appropriately describe the heat transfer phenomenon at the interface, the heat transfer at the interface between the microchannel heat sink, which is an ideally organized porous medium, and the finite-thickness substrate is examined. From the examination, it is clarified that the he heat flux distribution at the interface is not uniform for the impermeable wall with finite thickness. On the other hand, the first approach, based on the energy balance for the representative elementary volume in the porous medium, is physically reason able. When the first approach is applied to the thermal boundary condition, and additional boundary condition based on the local thermal equilibrium assumption at the interface is used. This additional boundary condition is applicable except for the very th in impermeable wall. Hence, for practical situations, the first approach in combination with the local thermal equilibrium assumption at the interface is suggested as an appropriate thermal boundary condition. In order to confirm our suggestion, convective flows both in a microchannel heat sink and in a sintered porous channel subject to a constant heat flux condition are analyzed. The analytically obtained thermal resistance of the microchannel heat sink and the numerically obtained overall Nusselt number for the sintered porous channel are shown to be in close agreement with available experimental results when our suggestion for the thermal boundary conditions is applied.

• 에너지공학
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• 제14권1호
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• pp.30-36
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• 2005

본 논문에서는 실린더 후류 영역의 열전달 특성에 대한 실험결과를 보고하였다. 정체점(θ=0°)로부터 실린더 뒷면(θ=180°)까지 국소 열전달을 측정하였으며, 축 방향에 대한 누셀트 수의 변화도 조사하였다. 덕트 중앙에 비하여 덕트 벽면근처의 후류영역 열전달계수는 58% 정도 높게 측정되었으며, 종횡비와 열전달 경계조건의 영향도 조사하였다.

• 설비공학논문집
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• 제1권1호
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• pp.64-72
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• 1989

Laminar natural convection heat transfer from a horizontal heat exchanger tube with one infinitely long vertical plate fin has been studied by a finite-difference numerical procedure. In predicting convective heat transfer from a circular tube, the thermal boundary condition at solid fluid interface is usually assumed to be isothermal. However, in reality, the thermal boundary condition is not isothermal, and the tube has the thickness and the conductivity. So the temperature at the interface is not known a priori to the calculation. This problem has the conjugate phenomena which occur between the tube conduction and external natural convection, and between the fin conduction and external natural convection. Numerical results are obtained to determine the effects of the conductivity of solid wall and the thickness of tube wall on heat transfer. It is found that the conduction causes significant influence on the natural convection heat transfer at low K and high ${\delta}$.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 제3회 압연심포지엄 논문집 압연기술의 미래개척 (Exploitation of Future Rolling Technologies)
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• pp.283-292
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• 1999

Temperature prediction model was developed for on-line application to plate rolling mills of POSCO. The adequate boundary conditions of heat transfer coefficients were obtained by comparing the predicted temperature with the measured temperatures taken by measuring system in plate rolling mill of POSCO. In obtaining the boundary condition which minimize the mean and standard deviation of the difference between prediction and measurement, orthogonal array for experimental design was used to reduce the calculation time of large data set. To predict the temperature drop at four edge of plate in one dimensional model, the energy change by heat transfer though directions perpendicular to thickness direction was treated like that by deformation. And the heat transfer through four edge directions was inferred from that through thickness direction with two coefficients of depth and severity of temperature drop at the edge. The boundary condition for the depth and severity of temperature drop were also determined using the measured temperature.

• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2230-2241
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• 2006

This paper presents a sole application of boundary element method to the conjugate heat transfer problem of thermally developing laminar flow in a thick walled pipe when the fluid velocities are fully developed. Due to the coupled mechanism of heat conduction in the solid region and heat convection in the fluid region, two separate solutions in the solid and fluid regions are sought to match the solid-fluid interface continuity condition. In this method, the dual reciprocity boundary element method (DRBEM) with the axial direction marching scheme is used to solve the heat convection problem and the conventional boundary element method (BEM) of axisymmetric model is applied to solve the heat conduction problem. An iterative and numerically stable BEM solution algorithm is presented, which uses the coupled interface conditions explicitly instead of uncoupled conditions. Both the local convective heat transfer coefficient at solid-fluid interface and the local mean fluid temperature are initially guessed and updated as the unknown interface thermal conditions in the iterative solution procedure. Two examples imposing uniform temperature and heat flux boundary conditions are tested in thermally developing region and compared with analytic solutions where available. The benchmark test results are shown to be in good agreement with the analytic solutions for both examples with different boundary conditions.

• Journal of Mechanical Science and Technology
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• 제18권6호
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• pp.1026-1035
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• 2004

An immersed boundary method for solving the Navier-Stokes and thermal energy equations is developed to compute the heat transfer over or inside the complex geometries in the Cartesian or cylindrical coordinates by introducing the momentum forcing, mass source/sink, and heat source/sink. The present method is based on the finite volume approach on a staggered mesh together with a fractional step method. The method of applying the momentum forcing and mass source/sink to satisfy the no-slip condition on the body surface is explained in detail in Kim, Kim and Choi (2001, Journal of Computational Physics). In this paper, the heat source/sink is introduced on the body surface or inside the body to satisfy the iso-thermal or iso-heat-flux condition on the immersed boundary. The present method is applied to three different problems : forced convection around a circular cylinder, mixed convection around a pair of circular cylinders, and forced convection around a main cylinder with a secondary small cylinder. The results show good agreements with those obtained by previous experiments and numerical simulations, verifying the accuracy of the present method.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.1888-1893
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• 2007

In this study, the microchannel plated heat exchanger were numerically studied for the enhancement of heat transfer in the channel configuration. Unit cold and hot fluid region with the microchannel were modeled and periodic boundary condition at the side wall was applied to continuously repeating geometry. The material of micro-structured plate is STS304 and working fluid is water. Triangular obstacles were placed in micro channel to enhance heat transfer. The performance of microchannel plated heat exchangers were numerically investigated with various obstacle configuration and Reynolds number under the parallel and counter flows. Heat transfer rate has increased about 18% compared with straight channel, but pressure drop also increased about 3.5 times. The main factor of increasing of pressure drop and heat transfer rate is considered that the momentum was lost to collide against obstacles, generation of secondary flow and boundary layer separation, wake and vortex forming phenomena.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제21권1호
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• pp.39-61
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• 2017

In this present article, we analyzed the heat and mass transfer characteristics of the nonlinear unsteady radiative MHD flow of a viscous, incompressible and electrically conducting fluid past an infinite vertical porous plate under the influence of Soret and chemical reaction effects. The effect of physical parameters are accounted for two distinct types of thermal boundary conditions namely prescribed uniform wall temperature thermal boundary condition and prescribed heat flux thermal boundary condition. Based on the flow nature, the dimensionless flow governing equations are resolved to harmonic and non harmonic parts. In particular skin friction coefficient, Nusselt number and Sherwood number are found to evolve into their steady state case in the large time limit. Parametric study of the solutions are conducted and discussed.