Water Dispersion by Hitting the Ribbed and Rounded Surfaces at the Low-Head Outflow Through a Small Hole

Ivan Pukhovyi

Abstract


Background. Low-pressure water spray by impact on a hard surface is convenient for crystallization of water on vertical surfaces and horizontal nozzles with icicles. In the previous works of the author, it was noticed the effect of an impact surface roughness on spray flow hydrodynamics, therefore, in this paper we investigate the effect of surface topography on the dispersion impact characteristics. The direction of drops movement along and across significantly affects the scattering drops parameters on the ribbed surfaces. This fact can be used in the irrigation of surfaces.

Objective. The work aims to investigate the effect of an impact surface topography and shape on the spray droplets flow hydrodynamics after the impact.

Methods. The experiments were conducted at a constant geometric height in the vessel 250–260 w.c. with the distance change from the impact surface to the hole from which water jet discharged at a cost in the range of 0.46–of 2.75 g/s. The height and the maximum radius of the droplets dispersion after impact were measured according to the evidence of the drops on a paper.

Results. We carried out the experimental studies of the drops dispersion characteristics: of the primary drops (after the discharge from small diameter holes) and of the secondary ones – after hitting the ribbed surfaces (flat, round, a roof), the convex and concave segment surfaces of sphere and cylinder. The drops scatter in 1.5–3 times further in the direction along the rib than in the perpendicular direction. We see farthest flying drops when using the ribbed roof. Impact on the surface with small ribs at low water flow rates and low heights of the jet fall does not give the desired results. The maximal height of the drops rising upward across the ribs is at a smaller distance from the impact center. The linear dependence of water flow on the pressure for the hole of1.6 mm diameter in the investigated range of water pressures was confirmed.

Conclusions. Under nozzles irrigation, there is a possibility of atomized flow distribution in the directions that allows ensuring the devices design requirements, for example, with pipes irrigation the ribs are placed along the edges of the pipes. Adjacent holes for the water flow are placed at a distance less than the maximum radius of the secondary droplets dispersion, given the lower irrigation density with increasing radius. If the vertical surfaces are irrigated, the distance from the impact center to the surface is selected depending on the irrigation density requirements and on the irrigation elementary point over the impact surface.


Keywords


Spray impact; Radius and height of spray drops; Ribbed and rounded impact surfaces; Nozzles irrigation for the icicles formation; Heat and mass transfer devices

References


I.I. Pukhovyi and A.M. Postolenko, “Dispergation of water stream at its small charges and forming of icicles on wire attachments”, Visnyk of Vinnytsia Politechnical Institute, no. 4, pp. 119–123, 2012 (in Ukrainian).

I.I. Pukhovyi and M.O. Krivosheev, “Flow and water freezing on vertical surfaces by drops irrigation obtained by blow spraying”, Naukovi Visti NTUU KPI, no. 6, pp. 29–35, 2012 (in Ukrainian).

M. Rein, “Phenomena of liquid drop impact on solid and liquid surfaces”, Fluid Dynamics Res., vol. 12, no. 2, pp. 61–93, 1993. doi: 10.1016/0169-5983(93)90106-K

L. Mishchenko et al., “Design of ice-free nanostructured surfaces based on repulsion of impacting water droplets”, Nanoletters, vol. 4, no. 12, pp. 7699–7707, 2010. doi: 10.1021/nn102557p

I.I. Pukhovyi, “Water dispersion and distinction of its low-head efflux down through the small hole”, Naukovi Visti NTUU KPI, no. 5, pp. 62–67, 2016 (in Ukrainian). doi: 10.20535/1810-0546.2016.5.79521

I.I. Pukhovyi and M.O. Krivosheev, “The proportion of the jet which is dispersed upon impact on a surface, for cooling water by air in ice-cold accumulator”, in Proc. ХІV Int. Sci. Conf. Renewable Energy of XXI Century, Kyiv, Ukraine, 2013, p. 121 (in Ukrainian).


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DOI: https://doi.org/10.20535/1810-0546.2017.2.96573

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