FLOW OF GAS-LIQUID FOAMS IN NARROW COMPLEX GEOMETRIES

Lead Research Organisation: University of Cambridge
Department Name: Chemical Engineering and Biotechnology

Abstract

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.
 
Description We have discovered that initially spherical bubbles contained in highly viscous liquids can distort into a variety of unexpected and, to the best of our knowledge undescribed, shapes when passing through a narrow constriction. Bubble shapes include shapes similar to "crescent moons". These shapes have been observed for single bubbles and bubble swarms and exist in both purely Newtonian liquids and also in viscoelastic liquids. It is conjectured that these bubble shapes will influence bubble coalescence behaviour. These deformations are well-predicted by a newly-developed theory, which assumes that bubble deformations are the same as for a liquid droplet replacing the bubble.

Furthermore, we have observed that there are significant differences in the behaviour of bubble swarms in Newtonian liquids and in viscoelastic polymers. These differences principally concern the extent to which flow-induced bubble coalescence occurs: this is higher in viscoelastic systems compared to Newtonian systems. When a bubbly viscoelastic liquid was flowed to-and-fro through a restriction orifice, the bubble structure was observed to almost completely degenerate, resulting in one or two large gas voids within the liquid polymer.

We have also found that existing computational fluid dynamics codes, such as OpenFOAM, cannot predict with accuracy these interesting bubble shapes. We have subsequently established modifications to the viscosity averaging method used in OpenFOAM that allows near-quantitative prediction of bubble shape. This has been tested against a variety of experimental data and found to be a significant improvement over the existing method. We found that the accuracy of the simulations are critically dependent on their resolution and but that successful simulations are able to give insight into the 3D structure of the bubbles that would be difficult to acquire experimentally.

Furthermore, we have also investigated the deformation and subsequent shape of thin soap films when they are impacted by a small, solid, object. We have established theory that describes the shape that these soap films take when they are deformed and that enables prediction of the falling object's behaviour. This theory has been validated against numerous experiments.

Finally, we have adapted image analysis codes to track the movement of individual bubbles and clusters of bubbles within dry foams. This yields information pertaining to the position, acceleration and deceleration of each bubble, from which information that is related to bubble topological change can be inferred. To the best of our knowedlge, this is the first time this particular method has been used to extract data of this nature from flows of foams. This method has been tested on foams flowing through a variety of constrictions and has demonstrated the irreversible nature of these flows.
Exploitation Route The observations resulting from this project concerning flow-induced bubble coalescence could be of relevance to a number of industrial sectors that are concerned with processing bubbly liquids and wish to obtain a predictable material structure. Oil field services companies could use this information to better understand how to control the microstructure of foamed concrete in oil well casings. Food manufacturers could also use these observations to ensure that edible aerated products have the desired mouth-feel: this is a consequence of microstructure. This could be taken forward by the existing industrial collaborators involved in the current project and other collaborators known to the PI. Discussons with new industrial collaborators are under way to assess interest levels.

The developments in the numerical simulation of two phase flows at very high capillary number and the bubble tracking methodologies that we used could be of interest to a number of groups in academia and industry alike. Further development of these approaches are planned in Cambridge, which could lead to the ability to model and measure the behaviour of bubble swarms, including coalescence and break-up phenomena.
Sectors Agriculture, Food and Drink,Chemicals,Construction,Manufacturing, including Industrial Biotechology

URL http://foamflows.org
 
Description SGR, Cambridge 
Organisation Schlumberger Limited
Department Schlumberger Cambridge Research
Country United Kingdom 
Sector Academic/University 
PI Contribution Schlumberger Cambridge research have agreed to support this research by access to facilities and expertise at an appropriate point in the project. This will be actioned at a point in the future of this project.
Collaborator Contribution Schlumberger Cambridge research have agreed to support this research by access to facilities and expertise at an appropriate point in the project. This will be actioned at a point in the future of this project.
Impact No outcomes yet.
Start Year 2016
 
Title Use of logarithmic mean viscosity averaging methods in volume of fluid codes 
Description This is an improved technique for use in computional fluid dynamics codes used to model two phase flows. It enables the shape and motion of a low viscosity entity contained in a very high viscosity continuous phase to be more accurately predicted compared to existing approaches. 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2018 
Impact Only used in house to date. Plans to make available to broader community once paper describing method has had peer review. 
URL http://foamflows.org
 
Description Project website 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact I created a website for the project such that key results and findings could be made available to the public. The intent is to publicise this website during future conferences and in academic publications or other engagement activities such that a wide audience can learn about the project.
Year(s) Of Engagement Activity 2017
URL http://foamflows.org/