Heat Transfer by Conduction and Radiation in a One-Dimensional Absorbing, Emitting and Anisotropically-Scattering Medium

1980 ◽  
Vol 102 (2) ◽  
pp. 303-307 ◽  
Author(s):  
W. W. Yuen ◽  
L. W. Wong
Keyword(s):  
Heat Transfer ◽  
Anisotropic Scattering ◽  
Total Heat ◽  
Approximation Technique ◽  
Dimensional System ◽  
General Effect ◽  
Total Heat Transfer ◽  
One Dimensional ◽  
The Common ◽  
Scattering Material

Heat transfer by simultaneous conduction and radiation in an absorbing, emitting and anisotropically-scattering material is investigated theoretically. Consideration is given to a one-dimensional system bounded by two parallel gray, diffuse and isothermal walls. Assuming a physical model of linear-anisotropic scattering, the resulting integral-differential equation is solved by a successive approximation technique similar to the method of undetermined parameters. The solution method is demonstrated to be relatively simple and yields solution converging qucikly to the exact results. Results show that for the present one-dimensional system, the common approach of treating the total heat transfer as a simple addition of separate independent contributions from conduction and radiation is quite inaccurate for certain cases. This approach is thus ineffective in illustrating the general effect of scattering. Both the scattering albedo and the forward-backward scattering parameters are shown to have some interesting effects on the total heat transfer and the medium’s temperature. The magnitude of these effects depends on the surface emissivity of the two boundaries.

Heat Transfer by Conduction and Radiation in Absorbing and Scattering Materials

1965 ◽  
Vol 87 (1) ◽  
pp. 143-150 ◽  
Author(s):  
R. Viskanta
Keyword(s):  
Heat Transfer ◽  
Radiant Energy ◽  
Dimensional System ◽  
Parallel Plates ◽  
Heat Transfer Characteristics ◽  
One Dimensional ◽  
System Parameters ◽  
Finite Distance ◽  
Radiant Energy Transfer ◽  
Scattering Material

Heat transfer by simultaneous conduction and radiation in thermal radiation absorbing, emitting, and scattering materials is investigated theoretically. Consideration is given to a one-dimensional system consisting of two diffuse, nonblack, isothermal parallel plates separated by a finite distance. The space between the two plates is filled with an isotropically scattering material. The problem is formulated exactly in terms of integrodifferential and integral equations. The results define as well as illustrate several mechanisms of radiant energy transfer and show how one mode of heat transfer influences the other. The numerical results reveal the effect of the system parameters on the heat transfer characteristics. In particular, it is shown that the effect of albedo on the heat transfer is small. Albedo being the parameter which represents the fraction of the incident pencil of radiation which has been scattered.

scholarly journals Combined Heat Transfer Mechanisms in the Porous Char Layer Formed from the Intumescent Coatings under Fire

Coatings ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 200
Author(s):  
Lingyun Zhang ◽  
Yupeng Hu ◽  
Minghai Li
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Thermal Conduction ◽  
Total Heat ◽  
Surface Radiation ◽  
Total Heat Transfer ◽  
Char Layer ◽  
Competition Result ◽  
Transfer Mechanisms ◽  
Combined Heat Transfer

This study examines the combined heat transfer by thermal conduction, natural convection and surface radiation in the porous char layer that is formed from the intumescent coating under fire. The results show that some factors, such as the Rayleigh number, conductivity ratio, emissivity, radiation–conduction number, void fraction and heating mode have a certain effect on the total heat transfer. In addition, the natural convection of the air in the cavity always inhibits surface radiation among the solid walls and thermal conduction, and the character of the total heat transfer is the competition result of the three heat transfer mechanisms.

scholarly journals Thermal analysis in thin-film fluid regions of rectangular microgroove

2018 ◽  
Vol 22 (2) ◽  
pp. 899-897
Author(s):  
Xiaohong Gui ◽  
Xiange Song ◽  
Baisheng Nie
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Flux ◽  
Contact Angle ◽  
Film Thickness ◽  
Flux Distribution ◽  
Total Heat ◽  
Heat Flux Distribution ◽  
Total Heat Transfer ◽  
Thin Film Thickness

The effects of contact angle and superheat on thin-film thickness and heat flux distribution occurring in a rectangle microgroove are numerically simulated. Accordingly, physical, and mathematical models are built in detail. Numerical results indicate that meniscus radius and thin-film thickness increase with the improvement of contact angle. The heat flux distribution in the thin-film region increases non-linearly as the contact angle decreases. The total heat transfer through the thin-film region increases with the improvement of superheat, and decreases as the contact angle increases. When the contact angle is equal to zero, the heat transfer in the thin-film region accounts for more than 80% of the total heat transfer. Intensive evaporation in the thin-film region plays a key role in heat transfer for the rectangle capillary microgroove. The liquid with higher wetting performance is more capable of playing the advantages of higher intensity heat transfer in thin- film region. The current investigation will result in a better understanding of thin- -film evaporation and its effect on the effective thermal conductivity in the rectangle microgroove.

scholarly journals Analysis of Thermal Properties on Backward Feed Multieffect Distillation Dealing with High-Salinity Wastewater

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Jianliang Xue ◽  
Qinqin Cui ◽  
Jie Ming ◽  
Yu Bai ◽  
Lin Li
Keyword(s):  
Heat Transfer ◽  
Thermal Properties ◽  
Total Heat ◽  
Total Heat Transfer ◽  
Steam Consumption ◽  
Capital Costs ◽  
Evaporation Temperature ◽  
Theoretical Investigations ◽  
Output Ratio ◽  
Salinity Wastewater

Theoretical investigations on thermal properties of multieffect distillation (MED) are presented to approach lower capital costs and more distillated products. A mathematical model, based on the energy and mass balance, is developed to (i) evaluate the influences of variations in key parameters (effect numbers, evaporation temperature in last effect, and feed salinity) on steam consumption, gained output ratio (GOR), and total heat transfer areas of MED and (ii) compare two operation modes (backward feed (BF) and forward feed (FF) systems). The result in the first part indicated that GOR and total heat transfer areas increased with the effect numbers. Also, higher effect numbers result in the fact that the evaporation temperature in last effect has slight influence on GOR, while it influences the total heat transfer areas remarkably. In addition, an increase of feed salinity promotes the total heat transfer areas but reduces GOR. The analyses in the second part indicate that GOR and total heat transfer areas of BF system are higher than those in FF system. One thing to be aware of is that the changes of steam consumption can be omitted, considering that it shows an opposite trend to GOR.

An Analytical Study of Heat Transfer in Finite Tissue With Two Blood Vessels and Uniform Dirichlet Boundary Conditions

2005 ◽  
Vol 127 (2) ◽  
pp. 179-188 ◽  
Author(s):  
Devashish Shrivastava ◽  
Benjamin McKay ◽  
Robert B. Roemer
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Source Term ◽  
Dirichlet Boundary ◽  
Total Heat ◽  
Dirichlet Boundary Conditions ◽  
Total Heat Transfer ◽  
Transfer Rates

Counter-current (vessel–vessel) heat transfer has been postulated as one of the most important heat transfer mechanisms in living systems. Surprisingly, however, the accurate quantification of the vessel–vessel, and vessel–tissue, heat transfer rates has never been performed in the most general and important case of a finite, unheated/heated tissue domain with noninsulated boundary conditions. To quantify these heat transfer rates, an exact analytical expression for the temperature field is derived by solving the 2-D Poisson equation with uniform Dirichlet boundary conditions. The new results obtained using this solution are as follows: first, the vessel–vessel heat transfer rate can be a large fraction of the total heat transfer rate of each vessel, thus quantitatively demonstrating the need to accurately model the vessel–vessel heat transfer for vessels imbedded in tissues. Second, the vessel–vessel heat transfer rate is shown to be independent of the source term; while the heat transfer rates from the vessels to the tissue show a significant dependence on the source term. Third, while many previous studies have assumed that (1) the total heat transfer rate from vessels to tissue is zero, and/or (2) the heat transfer rates from paired vessels (of different sizes and at different temperatures) to tissue are equal to each other the current analysis shows that neither of these conditions is met. The analytical solution approach used to solve this two vessels problem is general and can be extended for the case of “N” arbitrarily located vessels.

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