Study on Annular Mist Flow in Pipe : 2nd Report, Behavior of Watet Film in the Non-equilibrium Region of Downward Annular Mist Flow with Low Water Flow Rate

Abstract

This experimental work concerns downward vertical annular mist flows which were made by injecting a small amount of water from a coaxal nozzle into a downward air flow. The apparent velocities were varied from 18.56 to 58.01 m/s for air and from 4.78×10-3 to 1.47×10-2 m/s for water. Axial distributions of the water film characteristics, i.e., the film thickness, maximum wave height, wave velocity and frequency were obtained by the electrical conductivity method. The distribution of the friction coefficients at the air-water film interface was obtained from the pressure drop of air flow. The mean and minimum thicknesses of water film increased gradually downward and attained a constant value at a distance x=(30∼100)d from the nozzle exit, where d is the pipe diameter. The interfacial friction coefficient decreased with x and attained a constant value at x=(50∼80)d. The non-equilibrium lengths mentioned above are considerably shorter than that determined on the basis of the axial distribution of the water mists, about 180d, in the first report