Investigation of annular liquid film flow in tubes with helical ribs and wires

In this paper the entrainment rate of liquid droplets into the core region of a two-phase annular mist flow is investigated in tubes with helically ribbed and wired inner surfaces, with the aim of improving evaporative heat transfer in various steam generators of once-through type. The results show that the entrainment rate in the tubes depends on the height, helical pitch, and number of ribs and wires, the gas velocity and the liquid flow rate, and that it decreases to about 40 percent of a smooth tube. So-called large disturbance waves on the surface of the liquid film flow are reduced in number and the surface is smoothed in the tubes. In addition, the waves change their original annular shape to the three-dimensional one. These characteristics could be the cause of the entrainment suppression described above. The suppression effect can be correlated with three nondimensional parameters. The pressure drop of the tow-phase flow through the tubes is influenced by some other factors as well as by the hydraulic diameter