To reduce heat losses from a horizontal isothermal cylinder of radius ri = 20 mm, which is located in a large room in which air can be considered as a quiescent medium at temperature T(inf)= 30oC, the cylinder is encased concentrically within a larger cylinder of radius ri = 30 mm. All surfaces are painted with a low emissivity coating.
If the surface temperature of the inner cylinder is Ti = 70oC, determine:
a) The rate of heat loss per unit length from the smaller cylinder before it is encased with the larger cylinder.
b) The reduction in heat loss per unit length after encasing the smaller cylinder within the larger cylinder and the corresponding surface temperature of the large cylinder.