POSTHARVEST TECHNOLOGY 256 58 LANDTECHNIK 4/2003 Nozzles for Vegetable Washing

Ermyas Mulugeta, Martin Geyer, Bernd Oberbarnscheidt, Potsdam-Bornim, Robert Heinkel, Metzingen
V egetable washing with nozzles must be performed carefully in a short time with as little fresh water and energy as possible. The relation between the different factors of influence on the jet spray structure and the jet effect at the impact surface were analysed by a standard testing method developed in the context of a basic research, in order to show the possibilities of optimising the nozzles as well as the washing process. Materials and methods In the following article, results obtained
more » ... om the investigation involving two out of six selected washing nozzles are described. Nozzles with different flow rates were examined for water saving potential and thoroughness as well as gentle cleaning under conditions that are normal in vegetable washing in practice. The jet parameters of both nozzles were determined under varying operating parameters, at spray pressure (p) of 3, 5 and 8 bar, and at fixed nozzle distances (d) of 10 and 20 cm. An energetic analysis of the droplets formed in the jet spray was obtained. A standardised examination procedure for the evaluation of the jet parameters of the nozzles with regard to their surface efficiency was developed; this was accomplished by a recording of the dro-plet impulse distributions in the jet spray and their effect along the radial jet dispersion [11]. Results and discussions Influence of nozzle size under practically oriented spraying conditions The droplet spectra, formed through the variation of the examined quantities of the operational parameters, show relatively little differences within volume distributions of the droplets and the mean volumetric diameters respectively, referring to an optimal spray effect. The droplet distributions of the agricultural nozzle LU 90-04 show definitely more smaller droplets (30 ... 48% of total volume). This has a negative influence on the spray effect. In contrast to the agricultural nozzle LU 90-04 (spray bore (0,75 mm), the use of the industrial nozzle 632.726 (spray bore (1,7 mm) involves a decrease of the volume of droplets < 0,25 mm by 22 up to 34%, depending on the spray pressure (3 < p < 8 bar) and the examined nozzle distances. In the case of the industrial nozzle, this also results in a clear increase of the number of droplets > 0,25 mm as well as of the mean velocity for droplets or classes of droplets having the same size. The agricultural nozzle LU 90-04 is cha-racterised by a low volume flow rate and The drop spectra formed in the spray jet of various nozzles were tested on their energy and evaluated for their efficiency. Forming an efficient spray structure for vegetable cleaning is significantly defined by volume flow in combination with the nozzle distance.