PROBLEM S Problem 7.27. Liquefied petroleum gas (LPG) (assumed to be pure propane, for simplicity) in a partially insulated horizontal tube at a pressure of 7 bars. The tube diameter is

4 cm. The mixture mass flux is 197 kg/m³.s. Assume fully- developed flow, and thermally-developed conditions. At a location where the propane bulk temperature is equal to 120 K, the wall surface temperature is equal to 135 K. a) Find the frictional pressure gradient and convection heat transfer coefficient, using appropriate correlations of your own choice. Assume that the tube is hydraulically smooth. b) Repeat the calculations in Part a, this time assuming that the tube is coiled into a vertically-oriented helical configuration with R=25 cm and 1=10 cm. In part a, repeat the calculations this time assuming that the surface has a characteristic roughness of 50 μm.