Consider the tube and radiation shield of Problem 13.49, but now account for free convection in the gap between the tube and the shield, as well as for the fact that the temperature of the shield may not be arbitrarily prescribed but, in fact, depends on the nature of the surroundings. If the radiation shield is exposed to quiescent ambient air and large surroundings each at a temperature of 20°C, what is the temperature of the shield? What is the rate of heat loss from the tube per unit length?