Cleanability assessment of model solid surfaces with a radial-flow cell

The cleanability of several model solid substrates (glass, stainless steel, polystyrene and polytetrafluoroethylene—PTFE) was studied with a radial-flow cell. Two soiling methods were used to mimic splashing with oil; a thin layer chromatography sprayer giving a narrower and more reproducible oil droplet size distribution was preferred. Glass was the most cleanable substrate, a result which may be consistent with the presence of a swelling gel-like layer at the surface. For the other substrates, the mechanical action exerted by the fluid played a major role in oil removal; however the detergent seemed to intervene after about 5–10 min, facilitating cleaning of PTFE. Oil droplet removal took place only at high wall shear stress, in zones where flow conditions where not well controlled making it impossible to evaluate the wall shear stresses needed for oil droplet removal. Evaluation of cleanability by using the radial-flow cell is restricted to variations of wall shear stresses in a range below 3 N m−2.