Q (5: if the temperature of the inner wall 40° and the temperature
of the outer side at 20°. Find the heat rate transfer per unit area of
the wall if its thickness 250 mm. where is the emissivity factor (e=1),
and o Stephan's constant (0 = 5.67 x10 -8 J/s.m?.94) how tO find area and heat lost .