A laboratory test bench to analyse nozzle sprays

Aim of this study is to propose a low cost laboratory test bench, suitably designed to analysenozzle sprays according to the procedure described in ISO 5682-1. It consists of a transportabletrolley carrying a tank, a two diaphragms pump driven by an electric motor, and a spray boomcarrying one multiple nozzle holder. The spray boom may move, under the control of a DCmotor, along two slides placed above the working plane of the trolley. Acceleration anddeceleration ramps may be imposed by the speed controller. According to the proceduredescribed in ISO 5682-1, the test liquid is sprayed above Petri dishes placed on the workingplane and containing silicon oil: analysing the images of the drops captured inside the oil, it ispossible to measure the spray drop diameters and then all the spray features. The imageacquisition system is under development.Moreover, the test bench will be used to correlate spray features to water sensitive paper (WSP)images. Spraying at the same time Petri dishes and WSPs, the image of drops inside Petri disheswill be correlated to images on WSPs, so allowing the calculation of unitary deposits from WSP.Finally, the tests bench will be used to experimentally validate a model describing the WSPbehaviour when sprayed with drops of assigned drop size distribution and volume mediandiameter. In this paper WSP images were produced by simulation, assuming some simplifyinghypotheses: spherical drops and circular stains randomly placed on the images. Three types ofspray were simulated (Fine, Medium and Coarse) with two drop size distributions (log-normaland Rosin-Rammler). The simulations showed that the unitary deposit can be derived from themeasured percentage of covered surface on the WSP images, but the knowledge of the volumemedian diameter of the drops is necessary, independently of the probability distribution functionof drop size.