• 대한기계학회논문집B
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• 제24권11호
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• pp.1428-1436
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• 2000

The absorption of vapor involves simultaneous heat and mass transfer in the vapor/liquid system. In this paper, a numerical study for vapor absorption process into LIBr-H$_2$O solution film flowing over helical absorber has been carried out. Axisymmetric cylindrical coordinate system was adopted to model the helical tube and the transport equations were solved by the finite volume method. The effects of operating conditions, such as the cooling water temperature. the system pressure, the film Reynolds number and the solution inlet concentration have been investigated in view of the absorption mass flux and the total absorption mass flux and the total absorption rate. The results for the temperature and concentration profiles, as well as the local absorption mass flux at the helical absorber are presented. It is shown that solution inlet concentration affected other than operation conditions for a mass flux.

• 대한기계학회논문집B
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• 제33권1호
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• pp.17-27
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• 2009

Water jet impingement cooling is used to remove heat from high-temperature surfaces such as hot steel plates in the steel manufacturing process (thermo-mechanical cooling process; TMCP). In those processes, uniform cooling is the most critical factor to ensure high strength steel and good quality. In this study, experiments are performed to measure the heat transfer coefficient together with the inverse heat conduction problem (IHCP) analysis for a plate cooled by planar water jet. In the inverse heat transfer analysis, spatial and temporal variations of heat transfer coefficient, with no information regarding its functional form, are determined by employing the conjugate gradient method with an adjoint problem. To estimate the two dimensional distribution of heat transfer coefficient and heat flux for planar waterjet cooling, eight thermo-couple are installed inside the plate. The results show that heat transfer coefficient is approximately uniform in the span-wise direction in the early stage of cooling. In the later stage where the forced-convection effect is important, the heat transfer coefficient becomes larger in the edge region. The surface temperature vs. heat flux characteristics are also investigated for the entire boiling regimes. In addition, the heat transfer rate for the two different plate geometries are compared at the same Reynolds number.

• International Journal of Air-Conditioning and Refrigeration
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• 제15권1호
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• pp.25-33
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• 2007

The investigation has been made into the prediction of heat exchange performance of a counter flow type double-tube condenser for natural refrigerant mixtures composed of Propane/n-Butane or Propane/i-Butane in a smooth tube and micro-fin tube. Under various heat transfer conditions, mass flux, pressure drop and heat transfer coefficient of the mixed refrigerants were calculated using a prediction method, when the length of condensing tube, total heat transfer rate, mass flux and outlet temperature of coolant were maintained constant. Also, the predicted results were compared with those of HCFC22. The results showed that the mixed refrigerants of Propane/n-Butane or Propane/i-Butane could be substituted for HCFC22, while the pressure drop and overall heat transfer coefficient of the refrigerants were evaluated together.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume II
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• pp.680-683
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• 2006

A one-dimensional planar model is considered of the atmosphere with multi-layer clouds illuminated by a mono-directional parallel flux of solar radiation. A new approach is proposed to radiation transfer modeling and daylight background formation for the atmosphere with such clouds that is represented as a heterogeneous multi-layer system each layer of which is described by different optical characteristics. The influence functions of each layer are determined by solutions of the radiation transfer boundary problem with an external monodirectional wide flux while the contribution of multiple scattering and absorption in the layer is taking into account.

• 대한기계학회논문집B
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• 제25권10호
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• pp.1451-1458
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• 2001

The effects of a specularly reflecting surface on the wall heat flux and medium temperature distribution are studied. The system is an infinite square duct enclosing an absorbing and emitting medium. The walls are opaque, and black or gray. The walls emit diffusely but reflect diffusely or speculary. Heat is transferred by the combined effect of conduction and radiation. The radiative heat transfer is analyzed using direct discrete-ordinates method. The parameters under study are conduction, to radiation parameter, optical depth, wall emissivity, and reflection characteristics. The specular reflection and diffuse reflection show sizeable differences when the conduction to radiation parameter is less than around 0.01. The differences appear only either on the side wall heat flux or on the medium temperature profiles for the range of this study. The differences on the side wall heat flux are observed for optical thickness less than around 0.1 However the differences on the medium temperate profiles are found for optical thickness greater than around 1. The difference increase with increasing reflectance. The specular reflection increases the well heat flux gradient along the side wall.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1725-1734
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• 1996

Experimental condensation and evaporation heat transfer coefficients were measured in a horizontal smooth tube and a horizontal micro-finned tube with HFC-134a. The test sections are straight, horizontal tubes with have a 9.52mm outside diameter and about 5000mm long. The micro-finned tube had 60 fins with a height of 0.12mm and a spiral angle of 25.deg.. The condensation test section was a double-pipe type with counter flow configuration. The evaporation test section employed an electic heating method. Enhancement factors which is defined as a ratio of the heat transfer coefficient for micro-finned tube to that for smooth tube, varied from 1.3 to 1.6(mass flux:110~190kg/m$^{2}$s) for condensation and 1.2 to 1.5 (mass flux:70~160kg/m$^{2}$s) for evaporation. The experimental data of condensation and evaporation heat transfer coefficients were compared to several empirical correlations. Based on these comparisons, modified correlations of the condensation and evaporation heat transfer coefficient for both smooth and micro-finned tubes were proposed.

• 조명전기설비학회논문지
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• 제23권1호
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• pp.85-91
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• 2009

본 논문에서는 배전계통에 사용되는 케이블 권선형 변압기에 전력계통에서 발생되는 서지나 고장전류에 의해서 변압기의 고압측 코일에 유도되는 전자력의 크기를 유한요소 전자계해석 프로그램(FLUX2D)을 이용하여 해석하고, 기계진동방정식을 이용하여 케이블형 권선의 고유진동주파수를 분석하였다. 변압기모델로서 1(MVA), 22,900/220([V]) 단상 외철형 Cable형을 선정하여, 권선의 각방향의 전자력을 분석하고, 고유진동 mode를 Transfer Matrix Method를 이용하여 계산하고 상용 프로그램(ANSYS)을 이용하여 분석한 결과와 비교하였다. 진동모드의 분석한 결과 제시한 수치해석 방법은 공학적인 오차범위 안에서 충분히 수용할 정도의 정확도를 보여주었다. 변압기 권선의 전자력과 진동모드 분석결과는 변압기의 절연설계 및 단락기계력에 의한 절연 구조 설계를 위한 유용한 자료로 활용될 수 있다.

• 한국농림기상학회:학술대회논문집
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• 한국농림기상학회 2003년도 춘계 학술발표논문집
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• pp.115-128
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• 2003

o What is the flux \ulcorner Flux is the transfer of a quantity per unit area per unit time. The quantities are mass, heat, moisture, momentum and pollutant in micrometeorology. Kinematic flux (Fluid). The reduction in wind speed due to frictional drag transfers momentum from the atmosphere to the surface, creating turbulence that mixes the air and transports heat and water from the surface into the lower atmosphere. (omitted)

• Architectural research
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• 제1권1호
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• pp.41-46
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• 1999

The configuration factors in the flux transfer method are applied to calculate daylight factors reaching a station point. To analyze the window equipped with a louver system, geometrical correlation is used for the length shielded by the louver. The space in front of a window is assumed to be an imaginary outdoor space for calculating the luminance of the louver system. The data calculated from this study are compared with SUPERLlTE simulation data and the scale model data. Scale model data are collected on the roof of the Engineering building at Korea University in Seoul under the uniform sky condition.

• 대한설비공학회지:설비저널
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• 제11권4호
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• pp.1-5
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• 1982

In this paper, a study is made of the steady laminar free convection boundary-layer equations on a sphere with uniform surface heat flux. To solve the boundary-layer equations, well-known Pohlhausen's simiarity solution for vertical plates is adopted just the same for spherical bodies by introducing twonondimensional parametric functions, so called azimuth functions. To determine the values of the azimuth functions which are expressed in series at the two points (the upper stagnation point and the equator), trial and error method is required. It is concluded that the heat transfer results are in good agreement with obtained from perturbation method and Von Karman-Pohlhausen method within the steady laminar free convection region for Pr=0.70.