Chapter 12 Radiation Heat TransferChapter 12 RADIATION HEAT TRANSFER View Factors 12-1C The view factor represents the fraction of the radiation leaving surface i that strikes surface j directly. The view factor from a surface to itself is non-zero for concave surfaces. Fij→12-2C The pair of view factors and are related to each other by the reciprocity rule where Ai is the area of the surface i and Aj is the area of the surface j. Therefore, F→Fji→AFA Fiijj ji=FAAF1 12221122121=⎯→⎯=12-3CThe summation rule for an enclosure and is expressed as where N is the number of surfaces of the enclosure. It states that the sum of the view factors from surface i of an enclosure to all
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