Download Foam Drainage: Microscale Flow in an Ideal Isolated System

Foam Drainage: Microscale Flow in an Ideal Isolated System
C. Clarke*, A. Lazidis, F. Spyropoulos, I.T. Norton
*Department of Chemical Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
̴120˚
FLOW
Drainage
The driving force for foam collapse
Aims
• Quantify how food grade surfactants and particles impact
liquid flow through foams on a microscopic scale
• Scale up to see how this impacts the drainage of liquid food
foams on a macroscopic scale
• Provide a visual technique to identify microscopic flow
characteristics (e.g. velocity, geometry, resistance), potentially
leading to more tailored foam control
Drainage Channels – Plateau borders & Nodes
• Fluid flow occurs through a network of channels which take on a
distinctive geometric shape as the liquid fraction decreases
• Each channel made up of the intersection of three films, and terminates
at a node with three additional channels
Plateau border
Node
Issues with Existing Work
• Existing experimental work looks at microscopic flow through ‘infinite’
Plateau borders that do not terminate in nodes[1][2]
• The only study (to this author’s knowledge) that observes flow velocity
through an isolated Plateau border and node uses a warped node shape
not described by theory[3]
• No exploration of changes to the shape of the border and node for food
grade formulations at typical flow rates
• Conflicting theoretical models describing resistance of nodes to liquid flow
1
Koehler, S. A., et al. (2004). "Foam drainage on the microscale II. Imaging flow through single Plateau borders." Journal of Colloid and Interface Science 276(2): 439-449.
Pitois, O., et al. (2005). "Liquid drainage through aqueous foam: study of the flow on the bubble scale." Journal of Colloid and Interface Science 282(2): 458-465.
3 Pitois, O., et al. (2008). "Node contribution to the permeability of liquid foams." Journal of Colloid and Interface Science 322(2): 675-677.
2
Why do nodes matter?
• Two main flow regimes exist in foams:
 Plateau Border Dominated: Main flow
impact from shape and surface rheology of
the Plateau border
 Node Dominated: Main flow impact from
shape, surface rheology and any extra
material blocking the node
• Probing both regimes may reveal characteristics that help to
clarify best choice of ingredients for foaming solutions
Some key methods of analysing foam drainage…
• Observation
• Electrical Conductance
• Only shows average liquid content with time
• Tomographic Imaging
• Even fasted acquisition times struggle due to foam instability
• Confocal Microscopy
• Limited depth of imaging and requires high optical clarity
• MRI
• Labelling components may influence their actions
Isolated Plateau Border Setup
• 3D printed setup adapted from the work of Pitois et. al.[1] to produce an
ideal Plateau border and node geometry
Connection to Syringe Pump for controlled flow rate
injection of foaming solution
Precision injection nozzle determining flow velocity at
entrance to Plateau Border
Angled ‘tripod’ arrangement to ensuring stationary
attachment of films at 120˚ to one another
Adjustable base to define length of Plateau border
1 Pitois,
O., et al. (2008). "Node contribution to the permeability of liquid foams." Journal of Colloid and Interface Science 322(2): 675-677.
Basic Imaging Using Setup
• Photron SA3 high speed camera
• White light illumination
• Image scale using syringe needle
Basic Imaging
• PB and Node shadow images
• 510μm diameter needle for
permanent scaling feature
• Interference fringes in films
showing localised thinning
Measuring PB Radius
• Plot horizontal intensity profiles at vertical intervals
• Apply geometric correction factor of: 2
1 Elias,
3
[1]
F., et al. (2014). "Elasticity of a soap film junction." Physics of Fluids 26(3): 037101.
Plateau Border Radius (μm)
0
TOP
100
200
300
400
500
600
700
800
Distance from Outlet (μm)
0
5000
10000
15000
0.35% Fairy Liquid
0.7% Fairy Liquid
20000
25000
BOTTOM
30000
PB Radius vs Distance from 0.4mm diameter Outlet for 0.35% and 0.7% Fairy liquid solutions at 0μl/min
900
Initial Results
• Testing the performance of the setup and beginning to
compare to theoretical models for PB geometry and node
resistance at varying flow rates
• Solutions of 0.7% and 0.35% Fairy Original washing up liquid
with 7.5% glycerol are currently used for their high
foamability and stability
• Flow rates from 0μl/min to 350μl/min are used (from free
drainage to forced drainage regimes)
Expansion
Pinch
Choosing different surfactants to influence flow
• Different stabilisation mechanisms of surfactants impact the flow
Proteins
LMWS Surfactants
• Rigid boundaries
 Large flow increase towards channel centre
 Lower average flow velocity
• Mobile boundaries
 More uniform flow between centre and edges
 Higher average flow velocity
Mobile
Nguyen, A. V. (2002). "Liquid Drainage in Single Plateau Borders of Foam." Journal of Colloid and Interface Science 249(1): 194-199.
Rigid
Ongoing…
• Use of proteins and other food grade
surfactants (e.g. egg white proteins, tweens…)
• Tests to assess the impact of blocking the
node on the flow (e.g. particles)
• Quantify node resistance and average flow
velocity using pressure measurements
• Visualise flow with fluorescent particle/dye
tracking
Koehler, S. A., et al. (2004). "Foam drainage on the microscale II. Imaging flow through single Plateau borders." Journal of Colloid and Interface Science 276(2): 439-449.
Any Questions?