• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.3
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• pp.230-237
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• 1981

임의의 기하학적형태 단면을 가진 수직덕트내 층류조합대류열전달에서 벽온일정인 경계조건에 대하여는 Nayak[12], Giuidice[13]의 유한요소법해가 있다. 본 연구는 경계조건으로 벽에서의 열플러스가 비균일(균일한경우 포함)한 경우를 대상으로 유한요소법에 의한 해석을 시도한 것으로 예시에서 보는 바와 같이 수직해는 벽해밀과 좋은 일치를 보이고 있다.

• Fire Science and Engineering
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• v.8 no.1
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• pp.9-20
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• 1994

To understand the phenomena of laminar diffusion flame along vortical walt, the numerical analysis has been performed. Keller-box method was used to solve the problem in the boundary layer. The governing equation is simplified by thin-flame approxiamtion. And energy and chemical species equations are normalized with Schvab-Zeldovich variables. A physical domain is divided the boundary layer along streamwise coordinate as the combustion region and the propagation region. And Radiation model is concerned in these region. As a result, typical phenomena have been observed. Comparison of the numerical results with experimental data shows that the present method can successfully predict phenomena of laminar diffusion flame along upright surface.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.431-439
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• 1998

Falling film absorption process is an important problem in application such as absorption chillers. The presence of waves on the film affects the absorption process significantly. In the present study the characteristics of heat and mass transfer in laminar-wavy falling film were studied numerically. The wavy flow behavior was incorporated in the energy and diffusion equation. The numerical solution indicated that the interfacial wave increased the transfer rates remarkably. Interfacial shear stress and wave frequency seemed to be the dominant factors on the film Nusselt number and Sherwood number in the wavy film. A comparison of the transfer rates of the wavy film to that of the smooth film showed that the mass transfer rate could be increased by more than 50%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.7
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• pp.667-673
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• 2000

In order to understand the laminar flow heat transfer enhancement by the swirl flow, the effects of heat transfer in a circular pipe with a twisted tape insert were investigated experimentally. In the present study, the uniform heat flux condition was considered. The laminar heat transfer correlations were developed using the least-square-fit from the surface temperature distribution of an electrically-heated pipe and flow property data. Average Nusselt number correlations with the twisted tape insert were expressed as a function of swirl parameter, Reynolds number and Prandtl number. In the case of the twisted ratio y = 6.05, the mean Nusselt number increased approximately 500% and the friction factor increased approximately 300%, compared to the case of the empty pipe, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.1
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• pp.26-36
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• 1996

Many researches were carried out to estimate heat transfer rate on a circular cylinder in a uniform flow. Various empirical correlations were suggested in the past through experimental studies, however there are considerable discrepancies in the estimated values of heat transfer coefficient. The effect of fluid physical properties on the forced convective heat transfer between a circular cylinder and the external flow was numerically investigated in the present study, The flow and temperature fields were solved using a Finite Volume Method over a wider range of Prandtl number(0.7-40,000) than existing correlations. The cold as well as the hot cylinders in the uniform liquid flow of constant temperature were investigated. A unified correlation was obtainde for both cases.

• Journal of computational fluids engineering
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• v.7 no.3
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• pp.35-43
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• 2002

This paper addresses a numerical method for predicting transient temperature distributions in the wall of a curved pipe subjected to internal laminar thermally-stratified flow. A simple and convenient numerical method of treating the unsteady conjugate heat transfer in non-orthogonal coordinate systems is presented. Numerical calculations are performed for the transient evolution of thermal stratification in two curved pipes, where one has thick wall and the other has so thin wall that its presence can be negligible in the heat transfer analysis. The predicted results show that the thermally stratified flow and transient conjugate heat transfer in a curved pipe with a finite wall thickness can be satisfactorily analyzed by the present numerical method, and that the neglect of wall thickness in the prediction of pipe wall temperature distributions can provide unacceptably distorted results for the cases of pipes with thick wall such as safety related-piping systems of nuclear power plant.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.2
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• pp.147-159
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• 1982

내부에 정방형, 외부에 원형인 두 정온동심수평관으로 이루어진 폐쇄공간에서 열부력으로 야기된 대류열전달 현상을 연구하였다. 주어진 비정규적 형상에서의 층류 정상 Boussinesq 유동을 해 석하기 위하여, 지구중력방향에 대하여 가능한 두 개의 대칭형 위치에 관하여, Galerkin 유한요 소법을 사용하였다. 이론의 결과를 확증하기 위하여 실험적으로도 온도측정과 유선의 가시화를 수행하였다. 정방형내관의 직각인 선단은 국소 및 총체열전달에 있어서 소극적인 역할을 하지만, 이들로 인한 경계층 유동의 박리는 발생하지 아니함을 보였다. 이 내관의 상부 수평면상에서는 유동속도와 온도구배가 낮기는 하나 확연한 대칭형의 열상승류(Plume)가 가능하였다. 내관의 벽면들이 지구중력방향에 관하여 .+-.45.deg.의 각을 이룰 경우 과류의 중심부가, Rayleigh수가 6.5*$10^{4}$보다 작을 때는 4개, 이보다 클때는 2개가 폐쇄공간 안에서 발생하였다.

• Journal of the KSME
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• v.25 no.5
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• pp.413-418
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• 1985

직접 접촉식 교환장치(이하 직접 교환기라 함)에서 액체의 유통형태의 선택은 매우 다양하며 전달계수 역시 개별적인 상황이나 충전물의 종류에 따라서 달라지므로 일률적으로 제시되지 못 하고 있다. 많은 경우 실험을 통하여 열전달 또는 물질전달계수를 측정하게 되나 개수로, 자유 낙하액체막, 액체분류와 같이 이상화가 가능한 경우, 이러한 전달계수를 구하기 위하여 이론적 또는 반실험적인 해석을 수행하기도 한다. 수많은 관련 연구결과들은 층류유동에 관한 것과 난류유동의 경우로 구분되고(예상되듯이 대부분의 직접교환기의 유통영역은 난류쪽이다), 난류 유통의 해석은 다시 표면갱신이론(surface renewal model), 와류확산계수모델(eddy diffusivity model-macroscopic), 미분형와류모델(differential eddy diffusivity model)로 대별된다. 여기서는 수많은 교환기형태의 자료정리보다 상기와 같이 대별된 액체측 유동영역별로 전달현상해석의 방법을 간단히 정리하고자 한다.

• Journal of computational fluids engineering
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• v.19 no.2
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• pp.1-7
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• 2014

This study is to analyze the local convective heat transfer for a circular cylinder with annular fins. The relation between wall heat transfer and three-dimensional flow is investigated for different distances of annular fins. Depending on the fin spacing, the flow structure is strongly changed by the variation of horseshoe vortices. As the fin spacing increases, the heat transfer rate is maximized at a certain condition. This is clearly obtained as the Reynolds number increases, and it is closely related to the development of horseshoe vortices.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.5
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• pp.509-518
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• 2005

Liquid film thickness in laminar film condensation for flow over a flat plate generally is so thin that both fluid acceleration and thermal convection within the liquid film can be neglected. An integral solution method is proposed to solve the conjugate problems of laminar film condensation and heat conduction in a solid wall. It is found that approximate solutions of the governing equations involve four physical parameters to describe the conjugate heat transfer problem for laminar film condensation. It is shown that the effects of interfacial shear. mass transfer and local heat transfer are strongly dependent on the thermo-physical properties of the working fluids and the Jacob number.