Consider the cylindrical, 0.12-m-diameter radiation shield of Example 9.5 that is installed concentric with a 0.10-m-diameter tube carrying steam. The spacing provides an air gap of L = 10 mm.

(a) Calculate the heat loss per unit length of the tube by convection when a second shield of 0.14-m diameter is installed, with the second shield maintained at 35°e. Compare the result to that for the single shield of the example.

(b) In the two-shield configuration of part (a), the air gaps formed by the annular concentric tubes are L = 10 mm. Calculate the heat loss per unit length if the gap dimension is L = 15 mm. Do you expect the heat loss to increase or decrease?