FLOW OF GAS-LIQUID FOAMS IN NARROW COMPLEX GEOMETRIES

Gas-liquid foams 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, e.g. foam sclerotherapy of varicose veins, and expanding polymer foam for treating brain aneurysms. Thus, foams are crucial to a wide range of industries and contribute considerably to the world economy. For example, by 2018 the global market will be worth $61.9 billion for polyurethane foam, $7.9 billion for shaving foam, and $74 billion for ice cream. The chocolate market will reach $98.3 billion in 2016, and a considerable part of it is due to aerated products (e.g. mousse).

Foams are challenging complex fluids which are used for a variety of reasons including their light weight, complex microstructure, rheology, and transience, many aspects of which are not well understood and, thus, not well predicted by current models. A wide gap therefore exists between the complexity of foam phenomena and the present state of knowledge, which makes foam design and control in commercial applications more art than science.

In particular, in many industrial processes foams are forced to flow through intricate passages, into vessels with narrow complex cross-sections or through nozzles. Examples include flow of aerated confectionary in narrow channels and complex moulds, 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 advanced diagnostic techniques, and via theory and computer simulation a number of fundamental aspects related to the flow, stability and behaviour of three-dimensional foams through narrow channels containing a variety of complex geometries. The flow of aqueous foams as well as setting polymer foams with formulations of varying degrees of complexity will be experimentally studied. We will develop bubble-scale simulations with arbitrary liquid fractions spanning the whole range from dry to wet, to cover foams of industrial relevance. The wide range of experimental information and data to be generated in this project will allow these simulations to be guided and critically tested and, conversely, the simulations will underpin our engineering theory of the behaviour of foam flows in complex geometries.

This basic knowledge, from theory, modelling and experiment, will give a step improvement in fundamental science, and will assist designers and manufacturers of foam products, as well as designers and users of foam generating or processing equipment. More specifically, the practical aim of the project is to develop predictive tools as an aid to industrial practitioners, to describe the structural and dynamical properties of foams in terms of formulation properties and flow parameters, based on the knowledge gained from the experimental and modelling work. We will also work with our industrial partners to help them improve their understanding of the fundamental science which underpins their particular foam flow applications and, thus, enable them to enhance them.

Foam flow in complex geometries challenges our understanding of foam physics and behaviour. The complex foam structural instabilities and morphological transformations which tend to accompany such flows require further theoretical innovations in existing foam science, as well as industrial practice. The issues at stake engage, on the one hand, academic researchers looking to probe, understand and model these complex structured fluids, and, on the other, industrialists seeking to exploit their remarkable properties to develop new applications or enhance existing ones based on understanding rather than trial and error.

This project brings together complementary experimental, theoretical and computational expertise from Chemical Engineers and Mathematicians/Theoretical Physicists at three UK universities. Cambridge has a long track record of bubble mechanics, rheology and polymer processing. Birmingham, on the other hand, has a strong track record in experimental research on foams, multiphase systems and formulation engineering, whilst Aberystwyth has been a key international player in computational modelling of foams and complex fluids. We expect that the combination of our strengths will result in new interdisciplinary views and tools for the study of foams and multiphase systems in general, delivering high impact fundamental research across disciplinary boundaries between several EPSRC areas, including: Complex Fluids & Rheology, Soft Matter Physics, Fluid Dynamics, Process Engineering, Computational Physical Sciences, and Innovative Production Processes, which are related to several EPSRC themes such as Engineering, Manufacturing the future, Physical Sciences and Healthcare Technologies.

The experimental and theoretical methodologies developed here are mostly generic and therefore applicable to other types of flow geometries and two-phase systems, e.g. emulsions, gas-liquid flows. In addition, we can take advantage of and further develop our new proposed foam theory, as well as a range of new enhanced bubble-scale modelling methodologies introduced by one of us (Cox). These promising methods have not yet been adopted widely, mostly because they have only been applied to unrealistic slow flows of idealised two-dimensional dry foams. Here, we have an opportunity to use them to study industrially-relevant faster flows of real, three-dimensional, metastable foams.

There is still immense scope for foams to have greater impact on many industries, including food, consumer goods, pharmaceuticals, polyurethane, oil, ceramics, as well as other high value-added applications in the biotechnology and medical fields, e.g. sclerotherapy. This research is expected to impact all these industries by improving our understanding of the interrelations between foam deformation, microstructure and stability in complex flow situations, and by giving us the ability to predict foam behaviour. Based on the knowledge gained from the experimental and modelling work, the project will develop theoretical as well as simulation predictive tools as an aid to industrial practitioners.

More specifically, this research is supported by Unilever (food, personal care), BTG International (interventional medicine), Schlumberger (oil production) and P&G (consumer products). During the project, we will engage with all of them separately and collectively through quarterly meetings, tele/videoconferences, technical visits and data/info exchange to help them evaluate and develop new applications or enhance existing ones specific to their own businesses.

At the same time, we will use our results to enthuse school children and the general public about the value of scientific research and foam science to the UK, through the generation of outreach materials and a project website. Foams are a particularly appropriate vehicle for this sort of outreach, since they are familiar, fascinating, surprisingly ubiquitous and of great benefit to UK industry.