Cleaning of thick viscoplastic soil layers by impinging water jets
The removal of thick (approximately 1-10 mm) layers of three viscoplastic soft-solid food-related materials (a moisturising cream, Biscoff spread and smooth peanut butter) from polymethylmethacrylate plates by turbulent, coherent, 2 mm diameter water jets was studied for jet velocities of 10.6-25.4 m s-1 (10 500 < Re < 25 400). When the layer thickness was smaller than the nozzle diameter, soil removal involved the growth of a circular crater. With thicker layers, the removed soil initially formed a blister which subsequently ruptured, and removal by cratering followed. Blister formation and dynamics were studied for the moisturising cream using 2 mm and 3 mm nozzles, which indicated that this process could be described by simple geometric models. Tests with the moisturising cream on glass and stainless steel substrates indicated little effect of substrate on the removal behaviour. The rate of removal in the cratering regime was quantified by the kinetic model of Glover et al. (2016) and the effect of layer thickness on the kinetic parameters compared with the trend predicted by the model of Fernandes and Wilson (2020): qualitative agreement was evident. The results were used to revisit the study of blister formation by water jets impinging on Carbopol® layers reported by Tuck et al. (2019, 2020) and extract kinetic parameters from their data.