Y.M. John Chew

A scanning fluid dynamic gauging technique for probing surface layers

Fluid dynamic gauging (FDG) is a technique for measuring the thickness of soft solid deposit layers immersed in a liquid environment, in situ and in real time. This paper details the performance of a novel automated, scanning FDG probe (sFDG) which allows the thickness of a sample layer to be monitored at several points during an experiment, with a resolution of ±5 µm. Its application is demonstrated using layers of gelatine, polyvinyl alcohol (PVA) and baked tomato puree deposits. Swelling kinetics, as well as deformation behaviour—based on knowledge of the stresses imposed on the surface by the gauging flow—can be determined at several points, affording improved experimental data. The use of FDG as a surface scanning technique, operating as a fluid mechanical analogue of atomic force microscopy on a millimetre length scale, is also demonstrated. The measurement relies only on the flow behaviour, and is thus suitable for use in opaque fluids, does not contact the surface itself and does not rely on any specific physical properties of the surface, provided it is locally stiff.

Application of Fluid Dynamic Gauging in the Characterization and Removal of Biofouling Deposits

Green cleaning is generally defined as cleaning of a surface by consuming minimal resources in order to lessen the impact on human health and environmental quality. The main aim of this study is to perform cleaning studies of Escherichia coli biofilms grown on (i) polyethylene, (ii) stainless steel, and (iii) glass, to observe their removal behavior under controlled hydrodynamic conditions. The biofilms grown on the three different substrates were tested using the technique of fluid dynamic gauging, which allows for the estimation of the cohesive (within the biofilm structure) and adhesive (between biofilm and substrate) strength of the deposits. The results show that the thickness of biofilm on all substrates increases with time and plateaued at 14 days. Mature biofilms grown on glass have a stronger surface attachment than those on stainless steel and polyethylene. The results also suggest structural weakening after 21 days, implying either the death of cells or the weakening of the extracellular polymer matrix structure.