• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.5
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• pp.580-586
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• 2004

The ray effects of finite volume method (FVM) or discrete ordinate method (DOM) are known to show a non-physical oscillation in solution of radiative heat transfer on a boundary. This wiggling behavior is caused by the finite discretization of the continuous control angle. This article proposes a combined procedure of the Monte-Carlo and finite-volume method (CMCFVM) for solving radiative heat transfer in absorbing, emitting, and an-isotropically scattering medium with an isolated boundary heat source. To tackle the problem, which is especially pronounced in a medium with an isolated heat source, the CMCFVM is suggested here and successfully applied to a two-dimensional circular geometry.

• Journal of applied mathematics & informatics
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• v.42 no.3
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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.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.708-720
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• 2020

Core-wide temperature distribution in sodium-cooled fast reactor plays a key role in its decay heat removal process, however the prediction for temperature distribution is quite complex due to the conjugate heat transfer between the assembly flow and the inter-wrapper flow. Hybrid medium model has been proposed for conjugate heat transfer modeling in the core. The core is modeled with a Realistic modeled inter-wrapper flow and hybrid medium modeled assembly flow. To validate present model, simulations for a three-assembly model were performed with Realistic modeling, traditional porous medium model and hybrid medium model, respectively. The influences of Uniform/Non-Uniform power distribution among assemblies and the Peclet number within the assembly flow have been considered. Compared to traditional porous medium model, present model shows a better agreement with in Realistic modeling prediction of the temperature distribution and the radial heat transfer between the inter-wrapper flow and the assembly flow.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1381-1389
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• 1988

The heat transfer by simultaneous conduction, convection and radiation between flame and fuel surface in a thermally radiating medium is investigated theoretically. The flame and fuel surface are assumed to be diffuse, gray, infinite, isothermal, parallel surfaces separated by a finite distance. The space between the plates is supposed is formulated exactly in terms of simultaneous interior-differential equations. The numerical results reveal the effect of the system parameters on the heat transfer characteristics and the temperature distributions. The numerical results reveal that the optically thick radiating medium has a blocking effect on the total beat transfer. The temperature distributions are observed to be convex upward for an optically thick radiating medium as the alberto decreases.

• Journal of Mechanical Science and Technology
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• v.16 no.10
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• pp.1346-1354
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• 2002

The purpose of this work is to study the effects of specularly reflecting wall under the combined radiative and laminar free convective heat transfer in an infinite square duct. An absorbing and emitting gray medium is enclosed by the opaque and diffusely emitting walls. The walls may reflect diffusely or specularly. Boussinesq approximation is used for the buoyancy term. The radiative heat transfer is evaluated using the direct discrete ordinates method. The parameters under considerations are Rayleigh number, conduction to radiation parameter, optical thickness, wall emissivity and reflection mode. The differences caused by the reflection mode on the stream line, and temperature distribution and wall heat fluxes are studied. Some differences are observed for the categories mentioned above if the order of the conduction to radiation parameter is less than order of 10$\^$-3/ fer the range of Rayleigh number studied. The differences at the side wall heat flux distributions are observed as long as the medium is optically thin. As the top wall emissivity decreases, the differences between these two modes are increased. As the optical thickness decreases at the fixed wall emissivity, the differences also increase. The difference of the streamlines or the temperature contours is not as distinct as the side wall heat flux distributions. The specular reflection may alter the fluid motion.

• Journal of the Korean Society of Food Science and Nutrition
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• v.19 no.5
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• pp.375-380
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• 1990

It was attempted in this experiment to observe the effect of ginseng saponin on the growth and recovery rate of Saccharomyces rouxii which was shocked by heat-stress. The growth of S. rouxii was found most active when the saponin concentration in the malt extract broth was $10^{-3}%$ And the growth rate of S. rouxii grown on medium containing $10^{-3}%$ ginseng saponin was faster thanh that of the yeast grown on medium without saponin from the early log phase of the yeast. The growth recovery rate of S. rouxii which was heat-shockied by $80^{\circ}C$ - 30 minites was accelerated in the medium added ginseng saponin.

• Journal of Hydrogen and New Energy
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• v.28 no.6
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• pp.618-626
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• 2017

Conventional high temperature reformers are not suitable for hybrid fuel cell systems that use waste heat as a heat source. So, development of a low temperature type reformer is needed. However, the analysis was conducted in two ways to increase the thermal efficiency, because of low reforming rate due to the low heat source. First, it is a way to ger thermal gain from the outside through partial insulation. In the case of one heat source tube and several heat source tubes, we analyzed the effect of partial heat insulation in some cases. Second, we found the most efficient arrangement of the heat source tubes by changing the location of the heat source tubes. The interpretation was carred out using the COMSOL Mutiphysics program.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.2
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• pp.265-270
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• 1989

The present study considers the thermal structure variation in a porous medium caused by changing the most important radiative property of porous medium, absorption coefficient, as well as altering the physical dimension of porous medium and the equivalence ratio of premixed gas mixture. The radiation model was introduced as an unsteady differential form using the two-flux gray radiation model. The role of the conductive heat transfer through both gas phase and porous medium was found to be almost insignificant compared with that of the radiative heat transfer. The reaction zone shifted upstream and the flame thickness decreased as either the geometrical length of porous medium increased or the absorption coefficient decreased.

• Journal of Energy Engineering
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• v.9 no.1
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• pp.37-40
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• 2000

An inverse problem is solved to determine the space-dependent thermal conductivity in one-dimensinoal time-dependent heat conduction medium with the data imposed and measured at the two end-points. The thermal conductivity is approximated as a linear combination of known functions with unknown coefficients and the unknowns are obtained by the governing and sensitivity equations using modified Newton-Raphson method. The estimated results are compared with exact thermal conductivities and it shows good agreements. This approach is expected to be used to estimate spatial composition of heat conduction medium.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.11
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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.