Calculation of Direct Exchange Areas for Non-Uniform Zones

2003 ◽  
Author(s):  
Weixue Tian ◽  
Wilson K. S. Chiu
Keyword(s):  
Heat Flux ◽  
Computational Time ◽  
Thermal Gradients ◽  
Reasonable Accuracy ◽  
Radiation Heat ◽  
Radiation Heat Flux ◽  
Double Integral ◽  
Zonal Method ◽  
Direct Exchange ◽  
Transformation Of Variables

This paper presents a special transformation of variables to reduce a double integral into three single integrals and its use for calculating Direct Exchange Areas (DEA) in Zonal method. This technique was originally presented for calculation of DEA using a uniform zone system in a cylindrical enclosure. However, non-uniform zones are needed for applications with large thermal gradients. Thus we extended this technique to calculate the DEA for non-uniform zones in an axisymmetrical cylinder system. At least six times of saving in computational time was observed in calculating DEA compared with cases without transforming of variables. It is shown that accuracy and efficiency of estimation of radiation heat flux is improved when using a non-uniform zone system. Reasonable accuracy of all DEA are calculated without resorting to the conservative equations. Results compared well with analytical solutions and numerical results of previous researchers. A brief discussion of its application in calculating DEA in a 3-D rectangular enclosure is also provided.

Calculation of Direct Exchange Areas for Nonuniform Zones Using a Reduced Integration Scheme

2003 ◽  
Vol 125 (5) ◽  
pp. 839-844 ◽  
Author(s):  
Weixue Tian ◽  
Wilson K. S. Chiu
Keyword(s):  
Computation Time ◽  
Computational Time ◽  
Integration Scheme ◽  
Zonal Method ◽  
Similar Reduction ◽  
Direct Exchange ◽  
System A ◽  
Fold Reduction ◽  
Transformation Of Variables ◽  
Computational Resources

In the zonal method, considerable computational resources are needed to calculate the direct exchange areas (DEA) among the isothermal zones due to integrals with up to six dimensions, while strong singularities occur in the integrands when two zones are adjacent or overlaping (self-irradiation). A special transformation of variables to reduce a double integral into several single integrals is discussed in this paper. This technique was originally presented by Erkku (1959) for calculation of DEA using a uniform zone system in a cylindrical enclosure. However, nonuniform zones are needed for applications with large thermal gradients. Thus we extended this technique to calculate the DEA for non-uniform zones in an axisymmetrical cylinder system. A six-fold reduction in computational time was observed in calculating DEA compared with cases without a variable transformation. It is shown that accuracy and efficiency of estimation of radiation heat flux is improved when using a nonuniform zone system. Reasonable accuracy of all DEA are calculated without resorting to the conservative equations. Results compared well with analytical solutions and numerical results of previous researchers. This technique can be readily extended to rectangular enclosures with similar reduction in computation time expected.

Absorbed Radiation Heat Flux Sensors for Orbital Spacecraft. Algorithms for Measurement Data Processing

2021 ◽  
Vol 30 (3) ◽  
pp. 383-403
Author(s):  
A. V. Nenarokomov ◽  
D. L. Reviznikov ◽  
D. A. Neverova ◽  
E. V. Chebakov ◽  
A. V. Morzhukhina ◽  
...  
Keyword(s):  
Heat Flux ◽  
Data Processing ◽  
Measurement Data ◽  
Radiation Heat ◽  
Radiation Heat Flux ◽  
Heat Flux Sensors ◽  
Orbital Spacecraft

Radiation and Convection Heat Transfer in a Porous Bed

1968 ◽  
Vol 90 (1) ◽  
pp. 51-54 ◽  
Author(s):  
W. A. Beckman
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Collection Efficiency ◽  
Convection Heat Transfer ◽  
Heat Fluxes ◽  
Fluid Temperature ◽  
Radiation Heat ◽  
Radiation Heat Flux ◽  
Flowing Fluid ◽  
Porous Bed

The one-dimensional steady-state temperature distribution within an isotropic porous bed subjected to a collimated and/or diffuse radiation heat flux and a transparent flowing fluid has been determined by numerical methods. The porous bed was assumed to be nonscattering and to have a constant absorption coefficient. Part of the radiation absorbed by the porous bed is reradiated and the remainder is transferred to the fluid by convection. Due to the assumed finite volumetric heat transfer coefficient, the bed and fluid have different temperatures. A bed with an optical depth of six and with a normal incident collimated radiation heat flux was investigated in detail. The radiation incident on the bed at the fluid exit was assumed to originate from a black surface at the fluid exit temperature. The investigation covered the range of incident diffuse and collimated radiation heat fluxes expected in a nonconcentrating solar energy collector. The results are presented in terms of a bed collection efficiency from which the fluid temperature rise can be calculated.

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