Abstract
Radiation heat transfer plays an important role in the energy balance of plasma in an electric arc and its accurate prediction is essential for the development of new electrical devices. Unfortunately, a very complex spectrum of the absorption coefficient makes accurate radiation heat transfer calculations a very challenging task, especially with complex geometries. Numerical approximation of the absorption coefficient is therefore commonly used to reduce computing demands. This paper presents our contribution to the topic of computing requirements reduction, namely the problem of frequency band selection for mean absorption coefficients (MACs). We show that, with the proper band distribution and averaging method, even a very low number of bands can be sufficient for an accurate approximation of the real radiation heat transfer. The band selection process is based upon numerical optimization with a mean value of each band being calculated as a line limited Planck MAC. Both the line limiting factor and associated characteristic plasma absorption length are investigated in detail and an optimal value equal to the three plasma radii is proposed. Tables for three bands mean absorption coefficients in air at the pressure of 1 bar and temperature range spanning from 300 K to 30 kK are included in this paper. These tables serve as input parameters for a fast evaluation of radiation transfer using either the P1 or discrete ordinates method (DOM) approximation with satisfactory accuracy.
Highlights
Radiation transfer plays an important role in many plasma processes and cannot be omitted in relevant numerical simulations
Radiation heat transfer plays an important role in the energy balance of plasma in an electric arc and its accurate prediction is essential for the development of new electrical devices
This paper presents our contribution to the topic of computing requirements reduction, namely the problem of frequency band selection for mean absorption coefficients (MACs)
Summary
Radiation transfer plays an important role in many plasma processes and cannot be omitted in relevant numerical simulations. Unlike NEC, this method includes the calculation of the radiation transfer in the absorbing parts and, can predict the amount of radiation escaping the plasma This method has not seen much widespread usage, as it relies on a very large database, which makes it difficult to use for more complex problems, especially ones with pressure gradients. Proper handling of the bands distribution and calculation of the effective value inside each band plays a critical role in the overall accuracy of the approximation method. Proposed a method for numerical optimization of both the band distribution and the effective value inside each band. This method could be probably the most accurate approximation in case of particular plasma composition and its temperature profile. The question of optimal objective function goes beyond the scope of this paper
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