Gas-liquid Two-phase Flow in Double-Tubes-Annular-Passage with Flow Obstruction : 1st Report, Effect of Flow Obstruction on Minimum Film Thickness)

Abstract

The effect of a flow obstruction was experimentally investigated on the minimum thickness of a water film formed on the outer surface of the inner tube of concentric double tubes, through an annular cross section of which air-water two-phase mixture flows vertically upward. The flow patterns concerned are slug, froth and annular flows. Two kinds of obstructions were used in this experiment ; one is a ring type obstruction and the other is a thin circular tube type spacer. The liquid film thickness is drastically decreased by the existence of a flow obstruction, i.e., to about 40 μm. The film thinning process and the dependency of film thickness upon flow patterns are found to be quite similar to those on the inner wall of a single circular tube with an obstruction . Furthermore, an increase in minimum film thickness near an obstruction is observed resulting from the existence of an upstream obstruction.