Maximum and mean droplet sizes in annular two-phase flow

Abstract

The initial drop size in an annular flow which is determined in terms of the mechanism of droplet generation by shearing off of roll-wave crests by gas flow can be larger than the maximum stable droplet size in forced convection pipe flow. In this case the droplet size is further determined by droplet disintegration mechanism. Disintegration of droplets in a gas stream has been studied by a number of researchers. Several disruptive mechanisms of droplet break-up have been suggested. Each of these controlling mechanisms was evaluated as applied to the annular flow. It was concluded that in a case of partial entrainment the maximum size of a fluid particle was mainly controlled by the action of the dynamic force a fluid particle experiences in a relative motion. Based on this dynamic force and the stabilizing effect of surface tension, a detailed method for predicting the maximum droplet size in annular flow was presented. The correlations for the representative droplet mean diameters as well as the size distribution were then developed. A comparison with experimental data covering a wide range of fluid and flow variables indicated that indeed the postulated droplet disintegration mechanism was the dominant factor in determining the drop size.