Question

The minimum number of view factors required to be known initially to calculate all Possible view factors for a 9 surface unsymmetric enclosure are _______

• A. 72
• B. 36
• C. 27
• D. 81

Answer 1

The correct option is B 36

$\text{View factors that need to be evaluated directly for 'n' surfaces}{=}^n{C}_2{=}^9{C}_2=36$
Note:
$\text{Total possible view factors are}81(9\times 9)$. Out of 81 unknowns, 9 unknowns can be determined using summation rule for each surfaces. Half of the remaining 72 unknowns can be determined by applying reciprocity theorem between each pair of surfaces. Thus only 36 view factors must be known initially to calculate all remaining view factors.