What is Shape Factor ?
Shape Factor is defined as the fraction of radiative energy that is diffused from one surface element and strikes the other surface element directly with no intervening reflections.
- It is a function of geometry only.
- It is also called view factor or surface factor or configuration factor.
F1-2 = Q1-2/Q1
F1-2 = fraction of energy leaving surface 1 and reaching surface 2.
Q1 = Rate of total energy radiated by surface element ‘1’.
Q1-2 = Fraction of rate of energy leaving surface element ‘1’ and reaching surface element ‘2’.
- A1F1-2 = A2F2-1
- It indicates that the net radiant interchange may be evaluated by computing one way configuration factor from either surface to the other.
Shape Factor of Some Important Surfaces
- Plane Surface = 0 (F11 = 0)
- Convex Surface = 0 (F11 = 0)
- Concave Surface ≠ 0 (F11 ≠ 0)
Important Points to Remember
- Shape Factor depends only on geometry of a body.
- 0 ≤ Fm-n ≤ 1
- When one body is completely enclosed inside the other body, then shape factor of inner body with respect to outer body is equal to 1.
- A1F1-2 = A3F3-2 + A4F4-2 ; if radiating surface A1 is sub-divided into A3 and A4 .
- A1F1-2 = A1F1-3 + A1F1-4 ; if receiving surface A2 is sub-divided into A3 and A4 .