Numerical Analysis Seminars: Exploiting fluid dynamics to study soft layers on surfaces in situ
7 March 2008 14:15 in eScience 034
Many surfaces in nature and industry develop coatings of unwanted material as a result of micro-organisms colonising them to form biofilms, or the conditions at the surface promoting reaction to form fouling layers that degrade the performance of the equipment. The economic cost and environmental impact of fouling and of cleaning (removing) can be substantial. There is therefore a need to understand the mechanisms by which these layers develop and decay, but experimental studies are often complicated by the fact that layers generated in a liquid environment are often highly porous and collapse when dried, or deform when contacted by a measurement stylus.
Our group has developed a simple technique to measure the thickness of soft fouling layers which allows us to locate the surface of the layer and thereby measure its thickness in situ and in real time. We can currently achieve measurement accuracies of +/- 10 micron which allows us to study the growth or swelling of biofilms, protein gels, milk-based foulants and polymer films. This fluid dynamic guaging technique exploits the flow characteristics of a siphon nozzle as it approaches a surface to locate the interface without touching it: it therefore mimics the operation of an atomic force microscope, albeit at micron length scales.
We have developed the technique (and stretched the analogy with atomic force microscopy) by using computational fluid dynamics simulations of the creeping and laminar flows of Newtonian fluids involved to calculate the flow field and thus estimate the stresses imposed on the surface. This allows us to determine the yield characteristics of the soft layers and other aspects of their microstructure.
The technique also works well when the bulk fluid is moving: we can track the development and destruction of fouling layers in ducts and thereby simulate real flow conditions. Our simulation work in this area has identified several challenges, which will be outlined is this presentation alongside some of the potential applications of the technique.
Contact David.Bourne@durham.ac.uk for more information