A hollow steel sphere contains 100 watt electrical

Question

QUESTION - 6 A Hollow steel sphere contains 100 watt electrical filament inside it for heating. The other relevant data are as follows-
Internal and external radius of the sphere = 0.24 and 0.32 m respectively.
Inner and outer surface film coefficient = 30 and 10 kcal /hr .m² .^oc respectively.
Thermal resistance of the metal is negligible and steady heat transfer to be assumed.

Find out the
Part -a - internal temperature of the sphere, if its outside temperature is 22 ^oc.
Part - b - increase in inside temperature of the sphere, if it is lagged by 0.025 m thick magnesia of thermal conductivity 0.055 kcal /hr.m .^oc while the surface film heat transfer co-efficient remain unchanged.