Effect of Surface Roughness on Hydrodynamic Characteristics of an Impinging Droplet

Abstract

The influence of surface roughness and impact energy on the hydrodynamic behavior of water droplets impinging upon dry and rigid surfaces of known roughness has been investigated experimentally. The influence of these two parameters on the droplet maximum spreading diameter, slip length during droplet recoil, dynamic contact angle, contact angle hysteresis, and apparent contact angle of droplets at rest has been determined. Based on the quantitative assessment, a correlation for the maximum spreading diameter in terms of the nondimensional parameter (We/Oh) and surface roughness ratio (R a/d o) was derived. We propose to use surface roughness “R a” rather than using the contact angle for correlation as contact angles cannot be known a priori, whereas surface roughness can be determined beforehand. The wetting state of a droplet depends on the combined influence of droplet impact energy and surface roughness. While increasing impact energy increases the spreading, higher surface roughness resists the droplet from spreading. Low impact energy and a smoother surface tend toward the Cassie–Baxter wetting state, whereas high impact energy and rough surfaces propel the droplet toward the Wenzel state of wetting.

Uncovering the Effect of Physical Conditions and Surface Roughness on the Maximum Spreading Factor of Impinging Droplets Using a Supervised Artificial Neural Network Model

“…Theoretically, a surface with greater resistance to fluid expansion would reduce the initial impact and liquid expansion. This result is consistent with prior studies conducted by Singh et al 68 Additionally, Figure 11a depicts a positive link between β max and Re, whereas Figure 11b depicts a negative association between β max and We, which is consistent with prior research. 69,70 However, as shown in Figure 11c, which is compatible with physical facts, θ may govern β max up to a certain level.…”

Evaluation of the evaporation route of a liquid droplet on Au coated and non-coated glass surfaces

“…During the evaporation process, there was no significant change in the base diameter of H 2 O droplets applied to the uncoated surface (this result is supported by reference [31] ), but a significant change was recorded with the droplet containing 3 wt% SNP, which demonstrated an occasional increase and decrease in base diameter with time, known as the slip-length and contact angle variations. [40,41] However, for the Au-coated surface, significant changes were observed for both the H 2 O and SNP drops, with a decrease in base diameter with time t. This demonstrates that the change in the base radius of the water drop ( )…”

Liquid–Solid Impact Mechanism, Liquid Impingement Erosion, and Erosion-Resistant Surface Engineering: A Review

“…an actual contact area of the solid-liquid interface to its projection on a flat surface. The philic/phobic behavior can be enhanced by surface roughness [64]. On the other hand, in a Cassie-Baxter state, air pockets can be trapped within the textured surface, and consequently, a droplet can remain on top of the surface asperities and form a higher apparent contact angle (Figure 2c).…”