A furnace of spherical shape is losing heat steadily and uniformly from its outer surface...

A furnace of spherical shape is losing heat steadily and uniformly from its outer surface of radius R to the ambient air at temperature T∞ with a convection coefficient of h, and to the surrounding surfaces at temperature Tsurr (all temperatures are absolute temperatures) . If T0 denotes the outer surface temperature, the boundary condition at the outer surface of the furnace can be expressed as

(a)

(b)

(c)

(d)

(e)