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VDI Heat Atlas · K2 View Factors

Abstract

The view factor ϕ 12 is a purely geometrical value which describes the fraction of the total radiation from a surface 1 that hits another surface 2; see Sect. 2.2 in Chap. K1 . So in almost all cases of thermal radiation heat transfer, the first step in the calculation procedure is to determine the view factor which is valid for the two surfaces under consideration. The general formula for the view factor is (1) $$\varphi _{12} = {1 \over {\pi A_1 }}\int_{A_1 } {\int_{A_2 } {{{\cos \beta _1 \cos \beta _2 } \over {s^2 }}{\rm d}A_1 \,{\rm d}A_2 } } ,$$ where s is the length of the straight line which connects two differential area elements, one on each surface (Fig. 1). β 1 and β 2 are the polar angles between the normal line of these differential elements and the connecting line. Equation (1) holds true for two arbitrary surfaces obeying Lamberts cosine law, i.e., ideal diffuse radiating surfaces. As the evaluation of Eq. (1) is elaborate and as only geometrical parameters are involved, a number of solutions of Eq. (1) exist for different groupings of surfaces. These solutions are ready for application; they are explained in the following.

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Title
VDI Heat Atlas · K2 View Factors
Book Title
VDI Heat Atlas
Book DOI
10.1007/978-3-540-77877-6
Chapter DOI
10.1007/978-3-540-77877-6_65
Part of
VDI-Buch
Volume
Editors
Authors
  • Dieter Vortmeyer (1_65)
  • Stephan Kabelac Send Email (2_65)
  • Author Affiliation
  • 1_65 Munich, Germany
  • 2_65 Helmut-Schmidt-Universität, Universität der Bundeswehr Hamburg, Hamburg, Germany
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