Question

With an increase in the thickness of insulation around a circular pipe, heat loss to surroundings due to

• A. Convection increases, while that due to conduction decreases
• B. Convection decreases, while that due to conduction increases
• C. Convection and conduction decreases
• D. Convection and conduction increases

Answer 1

The correct option is A Convection increases, while that due to conduction decreases

An insulation is added to the circular pipe, the outer surface temperature will decrease because of higher thermal resistance but at the same time the surface area for convective heat dissipation will increase causing more heat loss. These two opposing effect lead to an optimum insulation thickness.




As shown in figure, the rate of heat transfer increases then decreases with increasing the thickness of insulation. The radius of insulation at which maximum rate of heat loss to surroundings is called critical radius of insulation. It is denoted by $r_c$ . The difference between the critical radius of insulation $(r_c$) and the inner radius of a hollow cylinder is called critical thickness of insulation.