Vaporization Inside Horizontal Tubes

Abstract This paper reports an investigation carried out to determine the changes in the coefficient of heat transfer for the evaporation of a liquid flowing inside a heated horizontal tube. For this research, a semiworks apparatus was constructed, consisting of 48 ft of standard 1-in. copper pipe, provided with 12 individual steam jackets, steam traps, and condensate lines. In the benzene runs, the velocities ranged from 0.26 to 1 fps at the inlet and 80 to 240 fps at the outlet; in the water runs, the corresponding values were 0.27 to 0.85 and 205 to 540 fps. With moderate temperature differences, as the fluid is progressively vaporized, the local over-all coefficient at first increases, goes through a maximum, and then decreases sharply toward values typical of superheating dry vapor. Such “vapor-binding” is attributed to insufficient liquid to wet the wall, small droplets of liquid being carried down the center of the tube, as observed at the entrance to the glass return bend. With high temperature differences, the type of vapor-binding previously observed when boiling liquids outside submerged tubes, where (due to excessive temperature difference) a vapor film insulates the tube wall from the bulk of the liquid, was encountered.