A hollow pipe of 1 cm outer diameter is to be insulated by thick cylindrical insulation having thermal conductivity 1 W/mk. The surface heat transfer coefficient on the insulation surface is 5 W/m2K. What is the minimum effective thickness of insulation for causing the reduction in heat leakage from the insulated pipe? (IES-04)
a. 10 cm b. 15 cm
c. 19.5 cm d. 20 cm