Water at 120°F flows in an iron pipe 10 ft long, whose inner and outer radii are 1 /2 in. and ¾ in. The temperature of the surrounding air is 70°F.
(a) Assuming that the water temperature remains constant along the length of the pipe, compute the heat loss rate from the water to the air in the radial direction, using the following values. For iron, k = 10.1 lb/sec- °F. The convection coefficient at the inner surface between the water and the iron is hi = 16 lb/sec-ft-°F. The convection coefficient at the outer surface between the air and the iron is ho = 1.1 lb/sec-ft-°F.
(b) Suppose the water is flowing at 0.5 ft/sec. check the validity of the constant-temperature assumption. For water, ( = 1.94 slug/ft3 and cp = 25,000 ft-lb/slug-°F.