Spreading of Low Impact Velocity Droplet on Porous Surface

Abstract

Abstract-Droplet spreading on flat non-reactive surfaces is established; however, porous surfaces present a complicated case. Wetting of porous surface involves the simultaneous spreading and penetration of the droplet. The effect of low impact velocity (i.e <1 m/s) on dimensionless droplet diameter and dynamic contact angle has been experimentally observed in this study. Low impact velocity helps reducing the penetration of droplets into the droplets in case of porous substrates. In the low impact velocity range, the effect on contact angle is not significant. Dimensionless droplet diameter also shows similar behavior. I. INTRODUCTIONDroplet spreading has been studied for over a century [1]. surfaces with high Reynolds number and high Weber number, the droplet usually forms a radially spreading lamella and a circular rim around it due to capillary forces and viscosity effects [6].The droplet impact depends upon the impact parameters, properties of the liquid and also on the nature, topology and properties of the solid substrate. On dry surface some common outcomes of droplet impact may be droplet deposition, prompt splash, receding, partial or complete rebound [6]. Some new phenomena have also been observed like very thin gas layer in start of spreading, collision of two drops, bubble entrapment in spreading contacting line, lamella rupture in high velocity impacts, finger formation and periodic recoiling of droplet [6], [7].Phenomenological details of droplet spreading dynamics on flat solid surface below splashing threshold/ Initial phase of droplet impact are as follows:Rioboo et al. [8] described the droplet impact of Newtonian fluids on dry surfaces to be consisting of processes namely kinetic phase, spreading phase and relaxation phase. In the kinetic phase, liquid is compressed and shock wave is formed as shown in Fig. 1.. Increasing impact velocity and droplet diameter results in faster spreading while increasing surface tension and viscosity leads to slower spreading [9], [10]. The results suggest that at high Re no (>2000), and in the absence of splashing, Re no alone can represent the droplet deformation. This applies only if the surface roughness is very small in comparison to the film thickness. Otherwise film detachment will take place and hence splashing may occur. Increased roughness promotes splashing [7].During the spreading phase, the hemi-sphere changes into lamella which thickens and expands to obtain disk like shape and sometimes has a rim around it as shown in Fig. 2.The flow is directed from axial to radial direction. Generally, increasing the impact velocity and/or droplet diameter leads to faster spreading whereas increasing surface tension and/or viscosity results in slow expansion of droplet on the surface

Effect of process parameters on droplet spreading behaviour over porous surface

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An investigation on dissolutive wetting of porous urea surface

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Production and Characterization of Controlled Release Urea Using Biopolymer and Geopolymer as Coating Materials

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