Gas-Liquid Foam Through Straight Ducts and Singularities: CFD Simulations and Experiments

Abstract

Some industrial processes are associated with the flow of aqueous foams inside horizontal channels. Examples are found in the oil, food and cosmetic industries. This type of flow presents an important pressure loss, originated from the shear stress exerted by the channel walls. Foam flow is one of the most complex fluids. In a macroscopic point of view, the physical-chemical interaction between the bubbles can be related to some non-Newtonian models (Bingham law, power law, etc.) or an apparent viscosity. These last can represent the internal deformations of fluid elements when shear stress is applied. An experimental facility able to create this type of flow is not so easy to design. Many parameters must be taken into consideration. So, Computational Fluid Dynamics (CFD) constitutes an ideal technique for analyzing this kind of problem. The aim of this study is to validate the use of Computational Fluid Dynamics in order to correctly predict the pressure losses and the velocity fields of a foam flowing through a straight channel and singularities (fence and half-sudden expansion). Simulations for a realistic scenario: two-phase flow, change in the surface tension, bubble size, were undertaken. Obtained results showed that simulations are not able to accurately reproduce for such a complex fluid, the important aspects of this study, such as the pressure losses and the velocity fields. Therefore, an approximation to a Bingham fluid was made. For a foam flow quality of 70% and a velocity of 2 cm/s, the numerical results are justified by experimental evidence. Experiments have been done and predictions for the flow behavior are extrapolated. Results show that the software is able to recreate the behavior of foam flow through a straight channel and singularities. However, this approach is extremely sensitive to the choice of several parameters, like the apparent viscosity, the yield stress, the viscosity consistence, etc.

CFD Characterization of a Wet Foam Flow Rheological Behavior

“…The presented work summarized a numerical study of aqueous non-Newtonian foam flow in a horizontal channel of square cross-section. Its goal was to extend the previous work of Chovet [9][10][11][12] in an interesting particular numerical model of the rheological behavior of foam flow.…”

“…However, some previous studies show that a Bingham fluid can predict the behavior of a foam flow, only for low velocity and most of its results present a deviation of 25% and 50%. Then, we consider a power law of Herschel-Bulkley model and test its efficiency to describe such flow situations [9][10][11][12].…”

Wall Shear Stress Generated by Aqueous Flowing Foam

“…Indicated in previous works [3,8,6], the foam flowing through channels may be studied under three different regimes, as a function of the axial velocity. This property may be measured by the PIV technique.…”

Removal of Bacillus spores from stainless steel pipes by flow foam: Effect of the foam quality and velocity

“…Wall shear stress, especially due to this thin liquid film located between the wall and the foam flow, plays an important role in the characterization of the rheological properties of this foam, depending mainly on the bubble size and particularly on the volume fraction of the liquid (Chovet, 2015;Chovet et al, 2014). These properties can be used to understand the microorganism detachment phenomena, such as spores from solid surfaces.…”