An investigation in to batch cleaning using wash racks

Batch cleaning processes, using washing racks, were studied in two distinct phases; the distribution of flow within the rack to the formation of jets at the nozzles and the interaction of the jetted fluid with the surface. A pipe network approach was used to model the flow in the rack and the interaction of the fluid with the surface was studied using a specifically designed test rig. A stationary coherent jet was set up to impinge horizontally on to a vertical wall. White soft paraffin (WSP) was used as the soil material, an excipient commonly used in pharmaceutical processing. Three variables (flow rate, WSP thickness and water temperature) were controlled and chosen to match the conditions on an exemplar wash rack. Water with no added surfactant was used for all experiments. Flow rates were in the range 1–4 l min−1 which corresponded to Re = 5960–23840 for the 4 mm diameter jet used. The limits of WSP thickness and water temperature were set between 0.19 to 1.9 mm and 20 to 60 °C, respectively. Clean areas produced by each jet were measured using image processing and using this data the cleaning performance of each system was compared against each other. An energy framework was adopted to allow cleaning to be assessed in terms of efficiency which provides a framework for optimisation of the process.