viewfaktori

Viewfaktori, or view factor, is a geometric parameter used in radiative heat transfer and thermal radiation analysis. It represents the fraction of radiation leaving one surface that directly reaches another surface, taking into account geometry, relative orientation, distances, and any obstructions. The factor depends only on the shapes and positions of the surfaces and is independent of material emissivities or reflectivities.

For two diffuse surfaces i and j, the differential view factor is dF_ij = (cos θ_i cos θ_j) / (π r^2) dA_i dA_j, where θ_i and θ_j are the angles between the surface normals and the line connecting the differential areas, and r is the distance between them. The overall view factor F_ij is obtained by integrating over both surfaces. A key property is reciprocity: A_i F_ij = A_j F_ji. In a closed, nonparticipating enclosure, the sum of F_ij over all j equals 1 for a given i, and F_ii = 0.

Calculation methods range from analytic solutions for simple geometries to numerical techniques for complex ones, such as radiosity, the hemicube method, or Monte Carlo ray tracing. View factors are assembled into a matrix to determine radiative exchange and perform energy-balance calculations between surfaces.

Applications of view factors span building energy modeling, industrial furnaces and engines, solar collectors, and the thermal design of electronic equipment, where accurate accounting of direct radiative transfer between surfaces is essential.