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

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The reduction of resources needed for cleaning in food processing plants is economically and ecologically sensible. In this paper, the potential of the pulsating jet cleaning to increase the time-based cleaning efficiency is demonstrated through the identification of relevant process parameters. The influence of the frequency as well as of the duty cycle was studied at varied flow rate on a model soil, and a significant effect of the duty cycle has been demonstrated. With suitable pulsation parameters substantial savings of cleaning fluid are possible

Original scientific paper To meet consumer safety and high product quality there is a need of reliable cleaning processes in the food industry. To keep competitive position it is necessary to control costs of those cleaning in place (CIP) processes e.g. expenses for fresh and waste water, detergents and to minimize downtime of the production facilities. The removal of food soils with water droplet sprays are very little researched, especially the mathematical modelling. In this paper we show that the high pressure model of Leu et al. can be applied to low pressure spray cleaning of a food soil with marginal adaptations. We used an existing analytical model for the relation of cleaned width as a function of the standoff distance and considered the different structure of the water spray as well as a food specific cleaning behaviour. We validated the analytical model with experimental results by varying the equivalent nozzle diameter. Keywords: CIP; cleaning model; spray; water jet Analiza primjene modela za čišćenje s mlazovima vode na CIP postupkeIzvorni znanstveni članak Zbog sigurnosti potrošača i osiguranja visoke kvalitete proizvoda nužno je provesti pouzdane postupke čišćenja u prehrambenoj industriji. Za održavanje konkurentnog položaja potrebno je kontrolirati troškove tih cleaning in place (CIP) postupaka, na primjer troškove za slatku i otpadnu vodu, deterđente, i svesti na minimum vrijeme prekida rada proizvodnih pogona. Čišćenje mrlja od hrane raspršivanjem vode veoma je slabo istraženo, naročito matematički prikaz postupka. U ovom radu pokazujemo da se model visokog tlaka autora Leu et al. može, uz neznatne adaptacije, primijeniti na čišćenje mrlja raspršivanjem vode niskog tlaka. Primijenili smo postojeći analitički model za relaciju čišćene širine kao funkcije standoff udaljenosti i razmotrili različitu strukturu raspršene vode kao i specifično ponašanje mrlje pri čišćenju. Potvrdili smo analitički model eksperimentalnim rezultatima mijenjanjem promjera mlaznice.