The "crossed-strings" method of Hottel [13] provides a simple means to calculate view factors between surfaces that are of infinite extent in one direction. For two such surfaces (a) with unobstructed views of one another, the view factor is of the form. Use this method to evaluate the view factors F12 for sketches (b) and (c). Compare your results with those from the appropriate graphs and analytical expressions.

((ac + bd) - (ad + bc) 2w," F12 = A, A2 A2 Im + -4 m 6) (b) tal