• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.274-275
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• 2006

The IEEE std 738 and Cigre Electra documents are well known as the standard of calculating the ampacity of overhead conductors. Although these two standards use the same basic heat balance concept, they use different applicable methods to calculate ampacity ratings. This paper examines the concept of basic heat balance equation and the differences of each term of basic heat balance equation.

• Structural Engineering and Mechanics
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• 제29권6호
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• pp.673-687
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• 2008

In this paper, a thermo-viscoelastic problem in an infinite isotropic medium in two dimensions in the presence of a point heat source is considered. The fundamental equations of the problems of generalized thermoelasticity including heat sources in a thermo-viscoelastic media have been derived in the form of a vector matrix differential equation in the Laplace-Fourier transform domain for a two dimensional problem. These equations have been solved by the eigenvalue approach. The results have been compared to those available in the existing literature. The graphs have been drawn for different cases.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.457-462
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• 2003

It studies the non-structural crack factors that are produced in Steel Box Girder Bridge concrete floor plate using analytical method. It mainly studies humidity and design standard of concrete strength. It used MIDAS CIVIL Ver 5.4.0, a general structure analysis program that applies drying shrinkage rate of domestic road bridge design standard and standard value of creep coefficient, CEF-FIP standard equation and ACI standard equation from the aspect of creep, drying shrinkage and hydration heat to see the effect of the two factors on concrete crack and found the following result. The analytical results of this study showed that the initial stress, which was obtained by ACI standard, exceeds the allowable tensile stress between 5 to 18 days. This result means that even if a bridge is designed and constructed according to design standard, the bridge can have cracks due to various variables such as drying shrinkage, hydration heat and creep that produce stress in slab.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 추계학술대회 논문집
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• pp.25-28
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• 2008

Steam reforming reaction is a matured technology to get hydrogen from hydrocarbon fuels compared with other reforming reactions such as partial oxidation(POX), autothermal reforming(ATR). It is so endothermic that it needs heat source to activate the reaction. Due to the reaction characteristics, heat transfer limitation phenomena generally occur in the steam reformer. As one of new ideas, the effect of discontinuous gas feeding is investigated based on heat transfer characteristics. The new operating method is usually favorable at high GHSV region(i.e. over $10,000h^{-1}$). In order to numerically simulate the physical issues, numerical approach is adopted based on heterogeneous reaction model, two-equation model in energy equation, and other constitutive models in porous media.

• 설비공학논문집
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• 제2권4호
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• pp.316-326
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• 1990

The measurements of heat transfer and pressure drop were performed on ripple tube with air flow. The results with the tube were compared with the performance of smooth tube. The enhancements in heat transfer coefficient for ripple tube, being compared with smooth tube, was ranged from 7.4 to 39 percent. The local Nusselt number for the inner fin tube, being compared with that for smooth tube, varied from 7.4% to 39%, while the corresponding increase in friction factors were 4.1 to 8.1%. One of the most direct indications of Nusselt number of ripple tube is given as following equation: $$Nu=0.061Re^{0.75}Pr^{0.4}(Tb/Tw)^{0.5}$$ We can see that Nusselt number for ripple tube in this experiment is consistent with the theoretical one taken from Walkinson's equation at Reynolds number range from 8,000 to 20,000.

• 한국기계가공학회지
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• 제10권6호
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• pp.134-139
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• 2011

This study was conducted on the characteristics of fluid flow and heat transfer in the ribbed tube used for a steam power plant. It was assumed that the air is incompressible and therefore, its density is not variable according to temperature. In addition, the gravity was ignored. A commercial code of computational fluid dynamics was used and standard k-$\epsilon$ model was used together with the energy equation included to calculate heat transfer. As Reynolds No. was low at the velocity distribution in the axial direction, the air reached hydro-dynamically fully developed region shortly but high Reynolds No. yielded late full hydro-dynamic development. The velocity distribution and non-dimensional temperature distribution were all physically reasonable and thus had a good agreement with the experimental result.

• 플랜트 저널
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• 제14권1호
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• pp.42-46
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• 2018

The flow and heat transfer characteristics inside a solar chimney power plant system are analyzed in this article. 3-D model with the $k-{\varepsilon}$ turbulence closure was developed. In this model, to solve the radiative transfer equation the discrete ordinates radiation model was implemented, using a two-band radiation model. To simulate radiation effects from the sun's rays, the solar ray tracing algorithm was coupled to the calculation via a source term in the energy equation. Simulations were carried out for a system with the geometry parameters of the Manzanares power plant. Based on the numerical results, the velocity and temperature distributions were illustrated and the results were validated by comparing with experimental data of the Manzanares prototype power plant. Moreover, temperature profile of the ground surface of the system was illustrated.

• 대한기계학회논문집
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• 제19권11호
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• pp.2995-3002
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• 1995

The cooling problem of the hot internal pipe flow has been investigated. Simultaneous conduction, convection, and radiation were considered with azimuthally varying convective heat loss at the pipe wall. A complex, nonlinear integro-differential radiative transfer equation was solved by the discrete ordinates method (or called S$_{N}$ method). The energy equation was solved by control volume based finite difference technique. A parametric study was performed by varying the conduction-to-radiation parameter, optical thickness, and scattering albedo. The results have shown that initially the radiatively active medium could be more efficiently cooled down compared with the cases otherwise. But even for the case with dominant radiation, as the medium temperature was lowered, the contribution of conduction became to exceed that of radiation.n.

• 열처리공학회지
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• 제32권1호
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• pp.17-28
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• 2019

Jominy hardenability curves of low alloy steel containing less than 5 wt.% of alloying elements in total were calculated by applying Scheil's rule of additivity to pre-calculated isothermal transformation curve. Isothermal transformation curve for each phase in steel was approximated as a simple mathematical equation by using Kirkaldy's approach and all coefficients in the equation were estimated from experimental temperature-time-transformation (TTT) and/or continuous cooling transformation (CCT) data in the literature. Then jominy test with simple boundary conditions was performed in computer by applying the finite difference scheme. The resultant cooling curves at each location along a longitudinal direction of Jominy bar were applied to calculate phase fractions as well as mechanical properties such as micro Vickers hardness. The simulated results were compared with experimental CCT data and Jominy curves in the literature.

• 한국분무공학회지
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• 제26권4호
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• pp.171-181
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• 2021

This study presents a prediction methodology of thermodynamic properties by using RK-PR Equation of State in a wide range of temperature and pressure conditions including both sub-critical and super-critical regions, in order to obtain thermophysical properties for hydrocarbon aviation fuels and their products resulting from endothermic reactions. The density and the constant pressure specific heat are predicted in the temperature range from 300 to 1000 K and the pressure from 0.1 to 5.0 MPa, which includes all of the liquid and gas phases and the super-critical region of three representative hydrocarbon fuels, and then compared with those data obtained from the NIST database. Results show that the averaged relative deviations of both predicted density and constant pressure specific heat are below 5% in the specified temperature and pressure conditions, and the major sources of the errors are observed near the saturation line and the critical point of each fuel.