Question

Explain the concept of critical thickness of insulation with expression

Answer 1

The addition of insulation in some cases may reduce thermal resistance due to the reduction in convective thermal resistance because of increase in surface area as in case of cylinder and sphere. It may be shown that the thermal resistance actually decreases and then increases in some cases with the addition of

insulation.

The thickness upto which heat flow increases and after which heat flow decreases is termed as critical thickness. In case of cylinders and spheres it is called ‘Critical radius.


Let us consider a hollow cylinder provided with in insulation with inner radius ‘r,’ and outer radius ‘r’