Dynamics of Foam Flow Through Processing Equipment

Gas-liquid foams are structured two-phase fluids in which gas bubbles are separated by interconnecting thin liquid films, and the volume fraction of the continuous liquid phase is small in dry foams but can be substantial in wet foams. They are ubiquitous in our daily life and in industry. Applications range from food, consumer goods, pharmaceuticals, polymers and ceramics to fire-fighting, enhanced oil recovery, and mineral particle transport. Recently, applications have also emerged in the medical field such as foam sclerotherapy of varicose veins and expanding polymer foam for treating brain aneurysms.

In many industrial processes foams are forced to flow through processing equipment with intricate passages, into vessels with narrow complex cross-sections or through nozzles. Examples include flow of aerated confectionary in narrow channels and complex moulds, dispensing ice cream through a nozzle, dispensing foams from pressurised bioreactors, filling of cavities with insulation foam, flow of foamed cement slurries in narrow oil-well annuli, filling of hollow aerofoil sections with polyurethane foam to make aerodynamic tethers for communication and geoengineering applications, and production of pre-insulated pipes for district heating. These flows are typified by contractions and expansions which generate complex phenomena that can have important effects on foam structure and flow, and can lead to dramatic instabilities and morphological transformations with serious practical implications for foam sustainability during flow and processing.

Here, the flow characteristics of the foam at bubble scale are important, but the topological changes incurred and their effects on the rheology and flow of the foam are poorly understood. This proposal seeks to address this lack of understanding by studying experimentally, using a range of diagnostic techniques a number of fundamental aspects related to the formation, flow, stability and behaviour of three-dimensional foams through channels containing a variety of complex geometries. The flow of aqueous foams with formulations of varying degrees of complexity will be studied. The effects of scale will be studied using microfluidic flow circuits and associated visualisation facilities including microscopy, high speed video, Particle Imaging Velocimetry, rheometer with real-time visualisation cell, etc. The work will study the interfacial as well as bulk properties of foam including rheology, pressure drop, drainage, static and dynamic stability. We currently have strong collaborations in this field with Unilever, as well as Cambridge University and Abersytwyth University through a large multi-institutional EPSRC Grant. The student will have the flexibility to develop an exciting research programme within this industrially important area of two-phase flow.