Nitrogen at atmospheric pressure is to be heated from 60°F to 120°F in smooth-walled tubes whose inside walls are maintained at 140°F. If the inner diameter is I in. and the average velocity of the nitrogen is 28 ft/sec, what is the required tube length? If a shorter tube is required to accomplish the same degree of heating for the same volumetric flow rate, should the tube diameter be smaller or larger than
in.?