The cleaning action of stationary coherent liquid jets impinging (a) vertically downwards on horizontal plates, and (b) horizontally on vertical plates, was investigated using three soft-solid model soil layers: (i) PVA glue on glass and polymethylmethacrylate (Perspex) substrates; (ii) Xanthan gum on stainless steel; and (iii) petroleum jelly on glass. The liquid stream nozzle sizes, mass and volumetric flow rates and mean jet velocities investigated were: PVA, 2 mm, 17-50 g s(-1) (0.06-0.139 m(3) h(-1)), 5.3-15.9 m s(-1); Xanthan gum, 0.39-3.3 mm, 2.1-148 g s(-1) (0.008-0.53 m(3) h(-1)); 4.5-31.7 m s(-1); petroleum jelly, 2 mm, 7.8-50 g s(-1) (0.06-0.139 m(3) h(-1)); 2.5-15.9 m s(-1). For all three soils, rapid initial removal of soil from the jet footprint was followed by the growth of a nearly circular, clean region centred at the point of jet impingement. The rate of removal of soil decreased sharply when the cleaning front reached the hydraulic or film jump. The data for the radial growth removal stage were compared with a mathematical model describing removal of the adhesive soil layer, where the force on the cleaning front was evaluated using the result reported by Witsun et al. (2012): their theory gave the momentum of the liquid film; this momentum was balanced against the soil strength, giving a simple relation between the cleaned radius and time. All three soils showed reasonable agreement with the model, across the range of flow rates and temperatures studied. The kinetic constant in the model was sensitive to soil layer thickness and the nature of the soil. Cleaning tests on the petroleum jelly soils at different temperatures, and separate theological measurements, showed that the kinetic time constant for coating removal was proportional to the (critical shear stress)(-1.8). There was good agreement between resultsobtained with vertical and horizontal plates for the PVA and Xanthan gum soil layers. The petroleum jelly results differed, which is partly attributed to differences in preparing the layers of this theologically complex material

No abstract

The removal of layers of a model food soil (dried Xanthan gum containing fluorescent ZnS particles) by a vertical water jet impinging normally on to the plate, generated by a solid stream nozzle which moves across the plate was reported by Kohler et al. (2014). Their experiments investigated nozzle pressures from 0.5 to 2.0 barg; nozzle diameters from 0.84-2.66 mm, nozzle layer separation of 20 mm, and nozzle traverse speeds of 2.1-126 mm s(-1). The flow parameters and separation are smaller than those typical of industrial jet cleaning operations. The model developed by Wilson it al. (2014) [Chem. Eng. Sci, 109, 183-196] for cleaning of similar layers by a stationary impinging jet was modified to describe the case of moving nozzle. This new model predicted the trends observed in the experiments, and analysis of the data yielded a similar cleaning rate constant to that obtained previously for cleaning of similar layers by stationary jets. The model predicted a non circular cleaning front which matched that extracted from new experiments in which the flow was interrupted in order to capture this feature. The model allowed the cleaning performance indicators suggested by Kohler et al. (2014) to be expressed quantitatively: these indicated that higher nozzle traverse speeds give increased cleaning Lime, energy and liquid consumption performance

No abstract

No abstract