An experimental comparison of film flow parameters and cleaning behaviour of falling liquid films for different tilt angles

Efficient cleaning is crucial in the food industry due to increasing safety needs, cost pressure and diminishing size of production batches. In Cleaning in Place (CIP) systems different flow types provide the cleaning effect by interaction, wherein falling liquid films make a significant contribution to cleaning. The flow of falling films can be significantly influenced by the design of the surface and, for example, of the tilt angle. In a previous publication it was shown for a low tilt angle of 30 degrees that for resource efficient cleaning a low wetting rate is suitable. It was pointed out that mean wall shear stress and mean flow velocity have an influence on the cleaning progress. In this paper the investigations are extended to describe the influence of the surface inclination in the range of 30-90 degrees on the flow and cleaning behavior of zinc sulfide/Xanthan gum soil layers on stainless steel for film Reynolds numbers of 1190-3110. The results show that the tilt angle has a major impact on the film thickness, wall shear stress and the mean cleaning rate. Cleaning results for three different stainless steel surfaces show that a low surface roughness does not necessarily lead to a better cleaning result.