Splashing generation by water jet impinging on a horizontal plate

Abstract

The report of COVID-19 virus in municipal wastewater raises the question of whether viruses can become airborne during wastewater transport in sewer systems. The present work experimentally investigates a water jet impinging vertically onto a horizontal plate and the behaviours of the generated tiny droplets. Depending on whether the jet breaks into primary drops before the impingement, three regimes can be defined: non-splashing, jet-splashing and drop-splashing regimes. The splashing ratio, i.e., the portion of jet flow rate becoming splashing droplets, ranges from 1% – 70% in the drop-splashing regime, while it remains less than 2% in the jet-splashing regime. For the splashing droplets, their size and velocity distributions follow log-normal laws. Their diameters are mainly in the range from 0 to 0.3 of the impact jet or drop diameter with the median less than 0.1. Their velocities mostly range from 0 to 3.0 times of the impact velocity with the median around 1.0. The medians of both the dimensionless diameter and velocity of splashing droplets decrease with the impact Weber number. The ejection angles of splashing droplets obey a bell-shaped distribution with the maximum around 70° and the median ranging from 16° to 30°.

Microfluidic jet impact: spreading, splashing, soft substrate deformation and injection

“…. This is comparable to the deposition behavior described for droplets and macroscale jets impacting solids [51,60]. As impact progresses (t = 83 µs), the amplitude of the waves increases and lamella formation is seen (Figure 2, red arrow), sometimes to the point where asymmetric fingering edge formation can be seen, but no secondary droplets detach from the expanding liquid sheet (Figure 2, red circles).…”

“…Qian et al reported a jet splashing regime at W e jet = 617 (D jet = 6 mm) [51], almost twice as low compared to our findings (W e jet = 1340). In contrast, Trainer et al saw splashing of jets (D jet = 3 mm) above W e jet = 1500 [63], closer to our findings.…”

“…In contrast, Trainer et al saw splashing of jets (D jet = 3 mm) above W e jet = 1500 [63], closer to our findings. Therefore, we interpret that the low splashing threshold found by Qian et al is due to the disturbances observed in the jets that lead to break-up [51].…”

“…The large range of jets showed distinct impacting behavior depending on jet and substrate characteristics. We observed seven regimes, and characterized them in terms of the Weber number of the impacting jet (W e jet ) and substrate G. As the W e jet describes the relative contribution of the fluid's inertia compared to the surface tension, it is often used to determine splashing thresholds of impacting liquids [36][37][38]51].…”

“…Furthermore, it is known that microscale droplets show different impact behavior compared to macroscale droplets as the rim of liquid formed after the impact becomes comparable to the mean free path of air molecules [48][49][50]. In contrast to droplet splashing, studies on jet impact and splashing are limited, and reported values for the splashing threshold vary widely [51,52]. Furthermore, few studies have explored the splashing dynamics for substrates with different storage moduli [28,53,54], and it remains unknown how microscale jet behavior compares to macroscale jets.…”