• 대한기계학회논문집B
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• 제39권11호
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• pp.897-903
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• 2015

본 연구에서는 냉온 자극요법의 열전달 특성을 정량적으로 파악하고자 한다. 축대칭 비압축성 Navier-Stokes 방정식 및 에너지 방정식의 해법을 위해 SIMPLE 알고리즘에 기반을 둔 유한체적법을 사용하였다. 혈액의 관류를 고려하기 위해 Pennes bio-heat 방정식을 추가로 적용하였다. 다양한 온도조건에 따른 피부 아래 각 지점에서의 열 침투양상을 분석하였다. 수치해석을 통하여 다양한 입력온도들에 대하여 역치 온도에 도달하는 영역들을 발견하였다. 또한, 페니스 효과로 인하여 피부 심부로 갈수록 외부 자극에 대한 온도변화가 완만함을 확인하였으며, 진피부분의 온도가 역치에 도달하기 위해서는 온 자극 및 냉 자극은 47도 및 7도 내외로 주어져야 함을 발견하였다. 본 논문의 수치해석을 통해 구축된 데이터베이스는 경혈 냉온 자극 치료기의 최적설계 시에 활용된다.

• 설비공학논문집
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• 제21권11호
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• pp.613-620
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• 2009

The thermal stresses of a ceramic heat exchanger were analyzed numerically since the ceramic material is good in heat resistance but weak in the thermal stress. The analysis of thermal stress was conducted in the ceramic core with two boundary conditions depending on bolt jointing. The thermal stresses were computed by applying temperature and pressure distributions obtained from the numerical results of conjugate heat transfer to ANSYS WORKRBENCH. When number of bolt joining halls was reduced from $8\times2$ to $4\times2$, the maximum principal stresses decrease by 47.6~50.5% and increase in safety factors by 2.18~2.5 for ultimate tensile strength. Thus, it can be said that bolt joining halls should be minimized in ceramic heat exchanger to be efficient in reducing thermal stress. In addition, the width of particular gas flow passages were revised from 52 mm to 42 mm to reduce maximum thermal stresses since certain passages experienced high thermal stresses. From the revision, safety factors were increased by 13.8~14.1% for the boundary condition of $4\times2$ bolt joining halls. Therefore, it is suggested that thermal stress can be reduced by changing local geometry of a ceramic heat exchanger.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.946-948
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• 2002

최근 컴퓨팅 기술의 발전으로 3차원 복합열전달(conjugate heat transfer) 문제를 계산하는 수 치해석 기술이 어느 정도 가능해 졌지만, 실제적인 전력기기 내부의 온도분포를 수치적으로 계산하는 것은 탑재된 구성요소의 다양한 크기와 형상으로 인한 매우 복잡한 경계조건을 수반하고 조밀한 격자를 요구하기 때문에 공학적이지 않다. 이를 위하여 해석적 모델을 수립하여 전력기기 열설계를 위한 수치적 해석에 적용하는 방법이 널리 사용되고 있다. 본 연구에서는 열회로망법(Thermal Network Analysis, TNA)을 이용하여 전력기기 내부의 온도분포를 예측할 수 있는 프로그램을 개발하였다. 전류가 흘러 열이 발생하고 소산되는 주회로 성분들을 각각의 노드로 분할하는 절차를 확립하였고 열접촉저항과 주울열을 적절히 선정함으로써 실제 전류가 흐르는 회로망 내 온도분포를 계산하였다.

• 태양에너지
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• 제6권1호
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• pp.60-69
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• 1986

Two-dimensional finite difference numerical analysis is used to study conjugate natural convection heat transfer from a horizontal conducting tube with one vertical axial fin. By increasing dimensionless fin length ($L_F$), the mean total Nusselt number of the upward fin is slightly less than that of the downward fin at $L_F\;{\le}\;0.18$ and is higher than that of the downward fin at $L_F\;>\;0.18$. However comparing the upward fin and the downward fin with the no fin, the mean total Nusselt numbers of downward fin and upward fin at $L_F=0.30$ are increased approximately 4.01% and 5.51%, respectively. As Rayleigh number, Prandtl number and Biot number increase, the mean total and the mean tube Nusselt numbers are increased, but as wall thickness increases, the mean total and the mean tube Nusselt numbers are decreased. As the fin conduction parameter increases, the mean total Nusselt number is slightly increased because of increasing the mean fin Nusselt number.

• 한국전산구조공학회논문집
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• 제30권6호
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• pp.495-500
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• 2017

본 논문에서는 과도한 계산용량이 필요한 초음속 비행체의 비정상 열응답 해석을 수행하기 위한 준-비정상해석 기법을 소개한다. 준-비정상해석 기법은 연성 연계 기법과 복합 열전달 해석기법을 통합한 방법으로 계산시간 단축시키면서 동시에 정확도를 향상시키기 위해 고안되었다. 또한 준-비정상해석 시, 해석 구간을 분할하기 위한 기준시간을 결정하는 알고리즘을 고안하여 준-비정상해석 기법의 정확도를 향상시키고자 하였다. 본 논문에서는 준-비정상해석 기법을 평가하기 위하여 가상의 비행 시나리오에서 열응답 해석을 수행하였으며, 비정상 해석 결과와 비교 검증을 수행하였다. 무딘 물체의 표면 온도 및 정체점의 온도를 통해 각각의 기법의 차이를 도출하였다. 비정상 해석을 통해 도출한 정체점의 온도와 준-비정상 해석을 통해 도출한 정체점의 온도 차이는 11.4% 이내로 높은 정확도를 확보함과 동시에 28배에 가까운 계산시간을 단축시켜 해석 기법의 효율성과 정확성을 확보하였다.

• 대한기계학회논문집B
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• 제21권3호
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• pp.436-444
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• 1997

Three-dimensional conjugate heat transfer and particle deposition on a circular cylinder in the OVD process are numerically investigated. Flow and temperature fields are obtained by an iterative method, and thermophoretic particle deposition is simulated. Effects of the heat conduction in the cylinder, the rotation speed of the cylinder, and the traversing speed of torch on the deposition are studied. Effects of variable properties are also included. As the conductivity of the cylinder decreases, particle deposition rate and deposition efficiency greatly decrease due to the reduced temperature gradient. The rotation of the cylinder has no significant effect on the deposition due to the small diameter of the cylinder and low speed of rotation. Since the increase of the torch speed keeps the surface low temperature, the particle deposition increases with the traversing speed.

• 대한기계학회논문집B
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• 제29권9호
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• pp.1049-1056
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• 2005

A conservative pressure-based finite-volume numerical method has been developed for computing flow and heat transfer by using an unstructured grid system. The method admits arbitrary convex polyhedra. Care is taken in the discretization and solution procedures to avoid formulations that are cell-shape-specific. A collocated variable arrangement formulation is developed, i.e. all dependent variables such as pressure and velocity are stored at cell centers. Gradients required for the evaluation of diffusion fluxes and for second-order-accurate convective operators are found by a novel second-order accurate spatial discretization. Momentum interpolation is used to prevent pressure checkerboarding and the SIMPLE algorithm is used for pressure-velocity coupling. The resulting set of coupled nonlinear algebraic equations is solved by employing a segregated approach, leading to a decoupled set of linear algebraic equations fer each dependent variable, with a sparse diagonally dominant coefficient matrix. These equations are solved by an iterative preconditioned conjugate gradient solver which retains the sparsity of the coefficient matrix, thus achieving a very efficient use of computer resources.

• Nuclear Engineering and Technology
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• 제32권4호
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• pp.410-423
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• 2000

A two-dimensional numerical model is developed and applied to the LAVA-EXV tests performed at the Korea Atomic Energy Research Institute (KAERI) to investigate the external cooling effect on the thermal margin to failure of a reactor pressure vessel (RPV) during a severe accident. The computational program was written to predict the temperature profile of a two-dimensional spherical vessel segment accounting for the conjugate heat transfer mechanisms of conduction through the debris and the vessel, natural convection within the molten debris pool, and the possible ablation of the vessel wall in contact with the high temperature melt. Results of the sensitivity analysis and comparison with the LAVA-EXV test data indicated that the developed computational tool carries a high potential for simulating the thermal behavior of the RPV during a core melt relocation accident. It is concluded that the main factors affecting the RPV failure are the natural convection within the debris pool and the ablation of the metal vessel, The simplistic natural convection model adopted in the computational program partly made up for the absence of the mechanistic momentum consideration in this study. Uncertainties in the prediction will be reduced when the natural convection and ablation phenomena are more rigorously dealt with in the code, and if more accurate initial and time-dependent conditions are supplied from the test in terms of material composition and its associated thermophysical properties.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2983-2988
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• 2007

In the present study, the numerical investigation on the effects of water-mist characteristics has been carried out for the fire suppression mechanism. The FDS are used to simulate the interaction of fire plume and water mists, and program describes the fire-driven flows using LES turbulence model, the mixture fraction combustion model, the finite volume method of radiation transport for a non-scattering gray gas, and conjugate heat transfer between wall and gas flow. The numerical model is consisted of a rectangular enclosure of $L{\times}W{\times}H=1.5{\times}1.5{\times}2.0m$ and a water mist nozzle that be installed 1.8m from fire pool. In the study, the parameters of nozzle for simulation are the droplet size and the spray velocity. Finally, the droplet size influences to fire flume on fire suppression than spray velocity because of the effect of terminal velocity, and the optimal condition for fire suppression is that the droplet size and the spray velocity are $100{\mu}m$ and 20m/s, respectively.

• 설비공학논문집
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• 제24권12호
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• pp.867-874
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• 2012

In the present study, three-dimensional transient numerical simulations were carried out to improve the performance of a vehicle paint drying process. In order to describe the movement of a vehicle, the techniques of moving boundary condition and multiple reference flames (MRF) were used. For the validation of the numerical analysis, the predicted temperature on the surface of a vehicle was compared to the experimental data, and a good agreement was achieved. With validated numerical procedure, various operating conditions of the temperature and the flow rate of the supply air were investigated to improve the drying performance of the facility. It is shown that the optimization of the operating condition can lead to energy savings and faster line speed of the production.