# What is Shape Factor? Definition and Important Terms

## Shape Factor Definition

Topics Discussed:

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

Where,

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 the rate of energy leaving surface element ‘1’ and reaching surface element ‘2’.

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### Reciprocity Theorem

• A1F1-2 = A2F2-1
• It indicates that the net radiant interchange may be evaluated by computing a 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 the geometry of a body.
• 0 ≤ Fm-n ≤ 1
• When one body is completely enclosed inside the other body, then the shape factor of the inner body to the 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.

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