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An experimental study of liquid jet impingement on a moving surface : the effects of surrounding air pressure and fluid properties Moulson, Jeremy Bryce Taylor


The impingement of a high-speed liquid jet on a moving surface and the resulting deposition or splash is important in a variety of technical and industrial processes. Of particular interest is the coating of the top-of-rail surface, in the rail road industry, with a thin film of viscoelastic liquid friction modifier, by liquid jet impingement, to control friction and reduce wear at the wheel-rail interface, thereby reducing fuel consumption and maintenance costs. For effective operation it is required that the fluid deposited by the jet adhere to the surface after impingement. An experimental investigation into the effect of surrounding air pressure and fluid properties on liquid jet impingement on a moving surface was performed. The study was carried out with Newtonian liquids impacting smooth, dry surfaces. A variety of ambient air pressures, jet speeds, surface speeds, surface tensions, and liquid viscosities were studied. The interaction between the impinging jet and the moving surface was analysed through high-speed imaging. It was observed that, as is the case for Newtonian droplet impact, the surrounding air pressure plays a crucial role in the splashing behaviour of jet impingement. There exists a threshold pressure below which splash does not occur. It is proposed that for certain impingement conditions lamella detachment from the surface occurs due to aerodynamic forces acting on the leading edge of the lamella, which destabilizes the balance between surface tension and fluid pressure forces. It was observed that both the Reynolds number and Weber number were salient to the occurrence of lamella detachment, with lamella detachment having a non-linear dependence on the Reynolds number. Lamella detachment was prone to occur for intermediate Reynolds numbers as the Weber number was increased, bounded by regions of deposition at higher and lower Reynolds numbers.

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