• Journal of applied mathematics & informatics
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• 제42권3호
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• pp.607-623
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• 2024

This article studies the effects of heat generation/absorption and thermal radiation on the unsteady magnetohydrodynamic (MHD) Casson fluid flow past a vertical plate through rotating porous medium with constant temperature and mass diffusion. It is assumed that the plate temperature and concentration level are raised uniformly. For finding the exact solution, a set of non-dimensional partial differential equations is solved analytically using the Laplace transform technique. The influence of various non-dimensional parameters on the velocity are discussed, including the effects of the magnetic parameter M, heat generation/absorption Q, thermal radiation parameter R, Prandtl number Pr, Schmidt number Sc, permeability of porous medium parameter, Casson fluid parameter γ, on velocity, temperature, and concentration profiles, which are discussed through several figures. It is found that velocity, temperature, and concentration profiles in the case of heat generation parameter Q, Casson fluid parameter γ, thermal Grashof number Gr, mass Grashof number Gc, Permeability Porous medium parameter K, and time t have retarding effects. It is also seen that the magnetic field M, Thermal Radiation parameter R, Prandtl field Pr, Schmidt number Sc have reverse effects on it.

• 한국해안해양공학회지
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• 제6권1호
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• pp.40-50
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• 1994

가로흐름이 존재하는 천해역으로 방출되는 표면온배수에 의한 온도장의 정확한 예측을 위한 근해역 2차원 수치모형을 개발하였다. 개발된 모형은 4-방정식 난류모델로서 열적 시간상수에 대한 정보를 얻을 수 없는 2-방정식 난류모델의 단점을 극복하기 위하여 변동온도 자승 평균항 및 그것의 감쇠율에 대한 전달방정식을 2-방정식 모델의 전달방정식에 추가한 모델이다. 또한, 부력생성항 및 난류 열플럭스항을 도입하여 연직방향 확산현상을 고려하고자 하였다. 개발된 수치모형을 간단한 단면을 갖는 개수로 정상류의 경우에 대하여 적용하였으며, 그 결과를 기존의 실험결과 및 2-방정식 난류모델을 사용한 수치계산결과와 비교하였다. 4-방정식 모형에 의한 계산결과가 2-방정식 모형보다 실험결과와 잘 일치하였으며, 제트 포획 및 안정화 영역에서 온배수의 물리적 특성을 잘 재현하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.150.1-150.1
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• 2014

Showerhead is used as a main part in the semiconductor equipment. The face plate flatness should remain constant and the cleaning performance must be gained to keep the uniformity level of etching or deposition in chemical vapor deposition process. High operating temperature or long period of thermal loading could lead the showerhead to be deformed thermally. In some case, the thermal deformation appears very sensitive to showerhead performance. This paper describes the methods for robust design using computational fluid dynamics. To reveal the influence of the post distribution on flow pattern in the showerhead cavity, numerical simulation was performed for several post distributions. The flow structure appears similar to an impinging flow near a centered baffle in showerhead cavity. We took the structure as an index to estimate diffusion path. A robust design to reduce the thermal deformation of showerhead can be achieved using post number increase without ill effect on flow. To prevent the showerhead deformation by heat loading, its face plate thickness was determined additionally using numerical simulation. The face plate has thousands of impinging holes. The design key is to keep pressure drop distribution on the showerhead face plate with the holes. This study reads the methodology to apply to a showerhead hole design. A Hagen-Poiseuille equation gives the pressure drop in a fluid flowing through such hole. The assumptions of the equation are the fluid is viscous-incompressible and the flow is laminar fully developed in a through hole. An equation can be expressed with radius R and length L related to the volume flow rate Q from the Hagen-Poiseuille equation, $Q={\pi}R4{\Delta}p/8{\mu}L$, where ${\mu}$ is the viscosity and ${\Delta}p$ is the pressure drop. In present case, each hole has steps at both the inlet and the outlet, and the fluid appears compressible. So we simplify the equation as $Q=C(R,L){\Delta}p$. A series of performance curves for a through hole with geometric parameters were obtained using two-dimensional numerical simulation. We obtained a relation between the hole diameter and hole length from the test cases to determine hole diameter at fixed hole length. A numerical simulation has been performed as a tool for enhancing showerhead robust design from flow structure. Geometric parameters for the design were post distribution and face plate thickness. The reinforced showerhead has been installed and its effective deposition profile is being shown in factory.

• 대한토목학회논문집
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• 제30권1A호
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• pp.53-59
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• 2010

최근 들어 적외선을 이용하여 콘크리트 구조물의 결함 또는 공동 등을 평가하려는 비파괴 연구가 활발하게 진행되고 있으며, 이는 유지관리기법의 중요한 부분을 이루고 있다. 적외선 화상분석(Infrared Thermography)을 콘크리트 표면에 적용할 경우, 콘크리트의 표면온도는 표면을 구성하는 재질과 열적특성(비열, 열전도율, 열전달율)에 따라 그 응답이 다르게 나타나게 된다. 서로 다른 배합을 가지는 시멘트 모르타르에서는 공극률이 다르게 구성되고, 표면에서 공극률의 차이는 열에 노출된 뒤, 냉각되는 과정에서 열적 거동이 다르게 평가된다. 한편 이러한 공극률은 강도 및 염화물 확산계수와 같은 역학적/내구적 특성에 영향을 주기도 한다. 본 연구에서는 외부에서 열을 가하여 측정하는 능동방식(active type)을 이용하여, 표면의 온도변화를 분석하였다. 물-시멘트비 55%와 65%인 시멘트 모르타르 시편을 제작하였으며, 공극률, 압축강도, 염화물 확산계수 등의 물리적 특성값들이 평가되었다. 이후 동일한 실내조건(온도 $20{\sim}22^{\circ}C$, 습도 55-60%)에서 적외선 화상분석 기법을 적용하였다. 시간의 경과에 따라 공극을 많이 포함하는 시편의 경우, 표면 온도가 상대적으로 증가하였으며, 온도가 일정해지는 시점(임계시점)이 단축되고 있음을 확인할 수 있었다. 이러한 특성은 콘크리트와 같이 공극과 골재를 가지고 있는 복합재료의 품질 평가에 적용할 수 있음을 시사한다. 한편 공극률과 실험상수를 고려하여, 공극률에 따라 변화하는 임계시간에 대한 계산식을 제안하였다. 본 논문에서는 시멘트 모르타르의 공극량의 변화에 따른 물리적 변화와 이에 따른 열특성 변화가 논의될 것이다.

• 한국산업융합학회 논문집
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• 제7권3호
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• pp.233-240
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• 2004

This paper presents a feasibility study of a fresh air load reduction system by using an underground double floor space The system was introduced into a real building and was examined by the field measurement Judging from the measurements during three years(1999~2001), the state of the system operation was very stable through this period and it was clear that the system contributes to reduction of energy consumption for air-conditioning. Futhermore, a simulation model used the simple heat diffusion equation Was developed to simulate its thermal characteristics and performances The simulations resulted m air temperature in good agreement with the measurements. Also, from the result of numerical analysis, It is clear that the amount of heat supply by using this system is more than the amount of energy loss to the room above it. Therefore, it is concluded that this systems is very useful and the proposed numerical model can be used for the prediction of system thermal performance.

• 대한기계학회논문집B
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• 제22권1호
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• pp.61-69
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• 1998

Vapor Axial Deposition (VAD), one of optical fiber preform fabrication processes, is performed by deposition of submicron-size silica particles that are synthesized by combustion of raw chemical materials. In this study, flow field is assumed to be a forced uniform flow perpendicularly impinging on a rotating disk. Similarity solutions obtained in our previous study are utilized to solve the particle transport equation. The particles are approximated to be in a polydisperse state that satisfies a lognormal size distribution. A moment model is used in order to predict distributions of particle number density and size simultaneously. Deposition of the particles on the disk is examined considering convection, Brownian diffusion, thermophoresis, and coagulation with variations of the forced flow velocity and the disk rotating velocity. The deposition rate and the efficiency directly increase as the flow velocity increases, resulting from that the increase of the forced flow velocity causes thinner thermal and diffusion boundary layer thicknesses and thus causes the increase of thermophoretic drift and Brownian diffusion of the particles toward the disk. However, the increase of the disk rotating speed does not result in the direct increase of the deposition rate and the deposition efficiency. Slower flow velocity causes extension of the time scale for coagulation and thus yields larger mean particle size and its geometric standard deviation at the deposition surface. In the case of coagulation starting farther from the deposition surface, coagulation effects increases, resulting in the increase of the particle size and the decrease of the deposition rate at the surface.

• Bulletin of the Korean Chemical Society
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• 제20권8호
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• pp.897-904
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• 1999

We have presented the thermodynamic, structural and dynamic properties of liquid pentane isomers - normal pentane, isopentane, and neopentane - using an expanded collapsed atomic model. The thermodynamic properties show that the intermolecular interactions become weaker as the molecular shape becomes more nearly spherical and the surface area decreases with branching. The structural properties are well predicted from the site-site radial, the average end-to-end distance, and the root-mean-squared radius of gyration distribution func-tions. The dynamic properties are obtained from the time correlation functions - the mean square displacement (MSD), the velocity auto-correlation (VAC), the cosine (CAC), the stress (SAC), the pressure (PAC), and the heat flux auto-correlation (HFAC) functions - of liquid pentane isomers. Two self-diffusion coefficients of liquid pentane isomers calculated from the MSD's via the Einstein equation and the VAC's via the Green-Kubo relation show the same trend but do not coincide with the branching effect on self-diffusion. The rotational re-laxation time of liquid pentane isomers obtained from the CAC's decreases monotonously as branching increases. Two kinds of viscosities of liquid pentane isomers calculated from the SAC and PAC functions via the Green-Kubo relation have the same trend compared with the experimental results. The thermal conductivity calculated from the HFAC increases as branching increases.

• 대한기계학회논문집 C: 기술과 교육
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• 제1권2호
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• pp.179-186
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• 2013

혈액순환촉진, 심혈관계치료, 피부질환, 암세포억제 등의 의료분야에 원적외선 치료법이 광범위하게 활용되고 있다. 본 연구에서는 원적외선 치료에 효과적인 패널형 방사체의 발열부에 대한 열적 특성을 실험적으로 분석하였다. 발열선은 정상상태에서 절연피복에 $150mW/m^2$의 열유속으로 열에너지를 공급하여 절연피복은 발열선 온도의 20%에 도달하였다. 단열막 사용은 약 20%의 발열판 표면온도 증가효과가 있었으며 열시상수를 상승시켜 혈액순환촉진에 크게 기여하는 것으로 나타났다. 발열선의 배치간격이 발열부 설계에 중요한 인자이며 열확산의 중첩을 위해 발열판의 열전도계수와 밀도를 고려해야함을 알 수 있었다.

• 대한기계학회논문집
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• 제14권2호
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• pp.453-462
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• 1990

The interaction of forced convection-conduction with thermal radiation in laminar boundary layer over a plate fin is studied numerically. The analysis is based on complete solution whereby the heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum and energy in the fluid boundary layer adjacent to the fin. The fluid is a gray medium and diffusion(Rosseland) approximation is used to describe the radiative heat flux in the energy equation. The resulting boundary value problem are convection-conduction parameter N$_{c}$ and radiation-conduction parameter m, Prandtl number Pr. Numerical results are presented for gases with the Prandtl numbers of 0.7 & 5 with values of N$_{c}$ and M ranging from 0 to 10 respectively. The object of this study is to provide the first results on forced convection-radiation interaction in boundary layer flow over a semi-infinite flay plate which can be used for comparisons with future studies that will consider a more accurate expression for the radiative heat flux. The agreement of the results from the complete solution presented by E. M. Sparrow and those from this paper for the special case of M=0 is good. The overall rate of heat transfer from the fin considering radiative effect is higher than that from the fin neglecting radiative effect. The local heat transfer coefficient with radiative effect is higher than that without radiative effect. In the direction from tip to base, those coefficients decrease at first, attain minimum, and then increase. The larger values of N$_{c}$ M, Pr give rise to larger fin temperature variations and the fin temperature without radiative effect is always higher than that with radiative effect.

• 전자공학회논문지D
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• 제35D권10호
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• pp.29-38
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• 1998

본 논문에서는 CZ 방법으로 성장된 실리콘에서 임의의 열처리 과정 또는 VLSI 공정중에 발생하는 산소석출물(oxygen precipitates)의 성장 및 감소에 대한 모델을 유도하고 수치해석법으로 시뮬레이션을 수행하여 모델에 대한 타당성을 검증하였다. 확산제한 성장법칙(diffusion-limited growth law)과 DBET(detailed balance equilibrium theory)를 이용하여 산소 석출물의 성장률과 감소율을 유도하고 이를 CREs(chemical rate equations)와 PFE (Fokker-Planck equation)이 결합된 식에 적용하여 수치해석법으로 풀었다. 또한 어닐링 분위기에 따라 표면에서 일어나는 현상을 달리 고려해야 하는데, 특히 O₂가스 분위기에서는 산화막이 성장되는 조건을 고려해야 하므로 산화막 성장 모델과 산소 용해도 증가등의 영향을 고려하였다. 이 방법으로 기존의 결과보다 더 정확하게 깊이에 따른 산소 농도의 분포와 산소 석출물의 밀도분포 함수를 계산할 수 있었다.