Question

For the same type of shapes, the value of Radiation Shape Factor will be higher when surfaces are
1. More closer only
2. Moved further apart
3. Smaller and held closer
4. Larger and held closer

Answer 1

Correct Answer - Option 4 : Larger and held closer

Concept: 

Shape Factor F_1-2  means the fraction of radiation leaving the surface 1 and striking the surface 2.

Following points are important about Shape Factor

• Summation rule if a body is exchanging radiation by n surfaces by 

          F₁₁ + F₁₂ + ------ F_1n = 1

• Reciprocity theorem A₁ F₁₂ = A₂ F21​

Now in order to have a higher shape factor, it is clear that if the objects are held closer then there is a higher possibility that the radiation leaving one surface will reach another surface.

Another thing to be noted here is if the sizes are larger then the surfaces can offer more area to receive the radiation that is moving towards them. For example, if two parallel infinite surfaces are held closer to each other then the radiation shape factor between both surfaces is 1.