state gov TSPSC Polytechnic Lecturer Mock Test 2022 Heat Transfer Conduction Critical Thickness of Insulation
A 40 mm diameter electric cable of an Aluminium conductor of thermal conductivity 240 W/mK is to be insulated with rubber of thermal conductivity 0.15 W/mK. The cable is to be located in the air with a heat transfer coefficient of 6 W/m2K. The critical thickness of insulation will be
1
5 mm
2
25 mm
3
20 mm
4
15 mm