Experimental and numerical investigations of cleaning based on fundamental modelling of mass transfer

Abstract The removal of a model food soil, a soluble coffee extract, from stainless steel plates by the passage of cold water has been investigated for two geometries: in a radial flow cell, where the flow is laminar and steady (but not simple), and in a rectangular duct where the flow is turbulent and fully developed. The rate of removal is assumed to be controlled by diffusion in the liquid phase, i.e. convective mass transfer where the liquid is moving. The experimental cleaning data, based on the local time to clean, are compared with detailed numerical models, where CFD simulations provide the velocity field for the mass transport equation. The diffusion coefficient for the coffee soil is determined separately by two different methods. The radial flow cell exhibits two cleaning fronts, related to the presence of recirculation zones, while cleaning in the duct features striations associated with periodic turbulence patterns. The results indicate that modelling even the simplest removal mechanism is not straightforward.