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Assessment of Radiation Solvers for Fire Simulation Models Using RADNNET-ZM

  • Wai Cheong TamEmail author
  • Walter W. Yuen
Conference paper

Abstract

The paper presents a neural-network-based zonal method (RADNNET-ZM) for the analysis of radiative heat transfer in an arbitrary Cartesian enclosure with an isothermal, homogeneous, non-gray medium. The model accounts for the non-gray effect of absorbing species in a combustion environment and the geometric effect of any three-dimensional enclosures. The model is verified against benchmark solutions. Maximum local error is observed to be less than 4%. Prediction accuracy of an existing zonal radiation solver is assessed. Results demonstrate that RADNNET-ZM can provide a substantial improvement to zone fire simulation models for the prediction of radiative heat transfer without a significant increase in computation cost.

Keywords

Neural network Zonal method Non-gray Multi-dimensional Fire simulation model 

Nomenclature

.

aλ

Local absorption coefficient

Ai

Elemental area i

D

Grid size of discretization

eλb

Planck function

fv

Soot volume fraction

Fij

View factor between Ai and Aj

Fss,xx

Generic exchange factor (xx = pd, pp)

Lij,xx

Center-to-center distance between Ai and Aj (xx = pd, pp)

Lpd, x

Mean beam length between two perpendicular elemental areas (x = soot, gas)

Lpp

Mean beam length between two parallel elemental areas

nx, ny, nz

Dimensionless distances for Aj relative to Ai

\(P_{{{\text{CO}}_{2} }}\)

Partial pressure of CO2

\(P_{{{\text{H}}_{2}{\text{O}} }}\)

Partial pressure of H2O

Pg

Total pressure of an N2/H2O/CO2 mixture

\(\dot{q}_{\text{g}}^{\prime \prime }\)

Incident heat flux due to emission of mixture medium

\(\dot{q}_{\text{w}}^{\prime \prime }\)

Incident heat flux due to emission of wall

ss

Surface–surface exchange factor

SS

Total surface–surface exchange factor

Tg

Gas temperature

Tw

Wall temperature

\(X_{{{\text{CO}}_{2} }}\)

Mole fraction of CO2

X, Y, Z

Dimensions of an enclosure

Greek Symbols

α

Total absorptivity (sum of soot and gas absorptivity)

αs

Soot absorptivity

Δα

Gas absorptivity

βxx

Normalized mean beam length (xx = pd, pp)

λ

Wavelength

ε

Emissivity of gas mixture

σ

Stefan–Boltzmann constant

Subscripts

pd

Perpendicular

pp

Parallel

Notes

Acknowledgements

The authors would like to thank Kevin B. McGrattan for his constructive comments and valuable suggestions to this manuscript.

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Copyright information

© This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply 2020

Authors and Affiliations

  1. 1.Fire Research DivisionNational Institute of Standards and TechnologyGaithersburgUSA
  2. 2.Department of Mechanical EngineeringUniversity of California at Santa BarbaraSanta BarbaraUSA

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