b'after exiting the nozzle, the liquid stream is sheared by an air stream that surrounds the liquid jet with a concentric annulus, then two air streams impinge the atomised spray at an angle to create an oval spray pattern shape. Typical pressures for both the liquid and compressed air in these nozzles are between 8-20 psi (0.55-1.38 bar), lower pressures are desirable to prevent fine (small) droplets which are more easily swept away from the conveyor by the air barrier flow.Figure 1. Setup summary of the conveyor, nozzle, spray, and manipulation hardware.In the industry, a variety of boundary layer/air barrier mitigation devices have been used on board productionEXPERIMENTAL METHODS external-mix air-atomising nozzle which machines. A common and simpleThe high-speed conveyer consists offeatures a 0.020 (0.508 mm) diameter method is to place a metal plate atwo larger rollers, 6.0 (15.2 cm) influid orifice. The nozzle was operated few inches upstream of the nozzlesdiameter, and a bed of 25 smallerat 10 psi (0.7 bar) for both compressed spraying the additive fluid. Theserollers creating a supported flat sectionair and liquid for all investigations. As mechanical blocking plates are thinconstituting the test-section. The 4the work focuses on comparing the and set up in a range of conditions(10.1 cm) wide conveyer loops arounddifferent mitigation techniques, water at depending on the equipmentthe larger drums and is driven byambient temperature was used as the constraints of the machine. Theythe downstream large roller which isadditive for each test. This nozzle setup are placed as close as possible toattached to a motor. The conveyerproduces a volume flow rate of Q w= the moving web without touching it.speed was set at 2080 ft/min (10.562.2 gal/hr (8.3 lph), and compressed Another common mitigation methodm/s) for all tests performed. Theair flow rate of Q a= 1.65 scfm (45.3 is to use compressed-air blow-offpositioning of the spray nozzle andslpm) and is shown in Figure 2.nozzles to create a counter-flow airconveyer are show in Figure 1 and the sheet upstream of the additive spraynozzle was oriented to spray verticallyThe boundary layer manipulation to disrupt the developed boundarydown. As the conveyer reaches testingmethods are shown in Figure 1; which laser from presenting a significantspeed an air layer from the movingincluded 1) a baseline case with no air-barrier. These blow-off nozzlesIn thesurface interacts with the spray outmanipulation, 2) a blunt plate, 3) an are typically mounted to the sameindustry, aof the nozzle, hindering the dropletsupstream facing knife edge plate, structure as the additive nozzle, so arevariety offrom reaching the conveyer. Each4) a small cylindrical rod, and 5) a only a few inches upstream, and areboundarymitigation device was placed separatelyblow-off air-nozzle. The baseline case tilted between 20-60 deg upstream offlayer/airwith its interaction point of the air layerallows evaluation of the boundary layer vertical. In addition to these commonbarrierapproximately 110 mm upstream of thewithout manipulation and assessment air-barrier mitigation techniques, amitigationcenterline of the nozzle to evaluate itsof what might constitute an air-barrier. knife-edge plate angled upstream anddevices haveeffect on the air barrier and resultingThe blunt plate and blow-off nozzle small diameter rod placed close tobeen usedtransfer efficiency. were selected because they are often the web were tested for comparison;on boardused in the field, without detailed but these are not currently typicalproductionThe experiment setup focused aroundevaluation of their effect. Finally, the methods used in the industry. machines. a Spraying System Co. 1/4J+SUE15Aknife-edge and cylindrical rod set-upsWORLD PULP&PAPER 75'