Design, construction and testing assessment of a twin-fluid electrostaticinduction nozzle.

Research on atomization and sprays has typified liquid nozzles into three groups namely, hydrodynamic (or pressure), rotary and pneumatic (or two-fluid) atomizers. The two-fluid atomizers are distinguished from the other two groups based on their capability to atomize the highly viscous liquids as well as the independency existing between the liquid and gas flowrates. However, the sophistication of mixing and atomization processes within a twofluid atomizer has restricted their theoretical developments, which has currently dominated the experimental viewpoints. Hence, the design of a two-fluid atomizer follows the main features of a benchmark atomizer in order to achieve new upgrades. In this direction, the current research work takes account of the atomizer proposed by Law to produce electrically charged drops, which has also undertaken various investigations during the last two decades. Despite these studies, there are still missing points and phenomena in connection with hydrodynamic performance of the atomizer, which need clarification. The atomizer proposed in the present work contains two main distinctions of an annular liquid feed and a primary settlement gas chamber in comparison with the benchmark atomizer. This atomizer has been investigated using an experimental rig capable of providing simultaneous compressed air, liquid feed and electrical voltage. The results show that the hydrodynamic parameters, i.e. air pressure and liquid flowrate, have significant effects on the atomizer charging efficiency whereas the electrical voltages exhibits no important role on the atomizer hydrodynamic trends. The atomizer comprises optimal working points providing optimum air pressure, liquid flowrate and charging voltage beyond which the spray specific charge degrades. This issue verifies the formation of various phenomena within the atomizer (e.g. electrode wetting, air ionisation and direct charging) of which the care should be taken in order to achieve the best consistency between the hydrodynamic and electrical charging processes. The quantitative spray deposition data also confirm the inducement of electric charge on a metal or plant target surface when a charge spray plume approaches the target. The morphology of the target also affects the electric charge magnitude particularly on the targets having sharp points on which the charge accumulation and in turn a highly electric field gradient takes place. The charge inducement in practice and based on the qualitative images approves the refinement of a charged spray trajectory towards the targets which enhances the drop deposition in comparison with an uncharged spray.