This paper reports the development of a scanning fluid dynamic gauge (FDG), a non-contact measurement technique developed to track the thickness and deformation behaviour of fouling layers on solid surfaces in real time. The device is computer controlled and yields a measurement accuracy of ± 5 μm with a measurement interval of 10-15 s. The scanning facility allows multiple points on the surface to be monitored simultaneously, increasing the amount of data that can be obtained from a single test. Here, scanning FDG is used to study the swelling and subsequent cleaning of a proteinaceous food soil (egg yolk) in a simple enzyme-based cleaning formulation. Quantitative measures of extents of swelling and swelling rates, as well as removal rates, are presented, as are comparisons with simple gravimetric tests. Dynamic pH variation is used to demonstrate real-time monitoring of novel cleaning procedures using sFDG. Enzymes are shown to interrupt the swelling process so that the layer can be readily removed by fluid shear. This approach allows the cleaning formulation and protocol for a particular soft deposit to be optimised.
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