Faster ray tracing in the modeling of radiant heat transfer

Abstract

Ray tracing is used in calculations of radiant heat transfer to take account of the screening of radiation and also to determine the view factors of the radiation. In ray tracing by means of a finite-element mesh, the list of cells and boundaries that lie on the ray path may be generated. In standard ray tracing, the next cell is determined by checking the interaction of the ray with each possible face of the current cell contacted by the ray. The tracing of the ray may be accelerated on the basis that each ray passes over a similar trajectory to its predecessor and must intersect the same boundaries and cells at the beginning of its route. For each ray, determination of the next cell on its path entails checking the intersection with the face in the path of the preceding ray. If the ray does not intersect that face, the other faces are checked by the standard method. The proposed method is tested in calculating the geometric coefficients of the radiation in a model of a sectional furnace by means of a hexahedral mesh. In testing, both determinate and random methods of selecting the ray directions are chosen. Different numbers of rays from each face of the mesh involved in radiant heat transfer (the furnace walls, the surfaces of the blank and the rollers) are considered. The method with determinate choice of the directions is shown to be more effective with a greater number of rays. In the tests, between 221000 and 88 million rays are employed. In many cases (between 19.6 and 71.4% of the total), it is sufficient to check the intersection of the ray with only one of the five cells, and the first face is intersected by the ray. This method does not impair the accuracy of the results and is up to 30% faster.