Modelling the removal of a diffusive food soil

A diffusive food soil is one where the rate of removal is determined by mass transport.Cleaning of a model diffusive soil was studied in two geometries: (i) a radial flow cell, where the flow is steady (Reynolds numbers, < 1000) but features complex flow characteristics, such as recirculation zones; and (ii) a rectangular slit flow cell, at spanning the transition to turbulence (750-11,000).Experiments employed a dried layer of instant coffee on flat 304 stainless steel plates, subjected to steady flow of water at ambient temperature.Removal was monitored visually and the location of the cleaning front and the local erosion rate were calculated.A noticeable feature in the turbulent tests was the appearance of streaks in the soil in the streamwise direction, corresponding to the existence of striations in the flow structure.The experimental results are compared with numerical predictions where the local velocity and soil removal flux were evaluated in steady state using the ANSYS Fluent CFD tool for implementation in a moving boundary calculation.The agreement is good and highlights the need to include the motion of the cleaning front in simulations for this type of soil.