Dryout of Falling Liquid Film Flowing on a Plate and a Vertical Cylinder

Abstract

The disappearance of dryout region observed in liquid film flowing on an inclined wall (50mm width) was investigated experimentally. The film surface profile on the cross section vertical to the flow direction was measured by the needle contact method to investigate the effect of side wall on the critical Weber number We_C at which the dryout region shrinks to disappear. The results show that there exists a minimum film thickness observed at few milli-meters from the side wall, which is much smaller than that of Nusselt' s theory. To avoid such effect of side wall on the dryout phenomenon, the critical Weber number We_C was measured for the film flowing on the vertical plate (200mm width) without side wall and on the outer wall of vertical cylinder. The experimental results show that We_C is much smaller than that for the inclined plate. A simple theoretical consideration was conducted to consider the force balance including the gravitational force at the edge of the dryout region in order to expect the critical Weber number. The results approximate well the tendency of the experimental results dependent on the advancing contact angle and viscosity.