PRESSURE-DROP FOR FOAM FLOW THROUGH PIPES

Although foams are two-phase materials, conventional two-phase flow calculation methods produce results very seriously an error if applied to foams. The reason is that the flow of a foam is dominated by the properties of a thin boundary region, which produce the effect of slip; the bulk properties, which are used in conventional methods, are less important to overall flow behavior. The most important parameter controlling the flow of foam in a pipe is the slip-layer thickness, which may be estimated from the average bubble diameter and expansion ratio. A relatively simple model with three fixed parameters and a slip-layer thickness calculated from the average bubble size can predict the pressure drops for many flows to within a factor of 2 in most cases. Improving the performance of this model in any particular situation may be possible with careful selection of the parameters. Within the accuracy of this model, effects of pressure variation on flowing foams can be allowed for satisfactoryly by using averages of inlet and outlet properties and assuming isothermal expansion of bubbles. © 1990.