Effect of intensified cavitation using poly(vinyl alcohol) microbubbles on spray atomization characteristics in microscale

Abstract

In this study, cavitating flows inside a transparent cylindrical nozzle with an inner diameter of 0.9 mm were visualized, and the effect of cavitation on atomization characteristics of emerging sprays was investigated. Different patterns of cavitating flows inside the nozzle were visualized using a high-speed camera. In-house codes were developed to process the captured images to study the droplet size distribution and droplet velocity in different flow regimes. The results show that cavitating flows at the microscale have significant effects on atomization characteristics of the spray. Two working fluids, namely, water and poly(vinyl alcohol) microbubble (PVA MB) suspension, were employed. Accordingly, the injection pressures were detected as 690 kPa, 1035 kPa, and 1725 kPa for cavitation inception, supercavitation, and hydraulic flip flow regimes in the case of water, respectively. The corresponding pressures for the aforementioned patterns for PVA MB suspension were 590 kPa, 760 kPa, and 1070 kPa, respectively. At the microscale, as a result of a higher volume fraction of cavitation bubbles inside the nozzle, there is no large difference between the cavitation numbers corresponding to cavitating and hydraulic flip flows. Although the percentage of droplets with diameters smaller than 200 μm was roughly the same for both cases of water and PVA MB suspension, the Sauter mean diameter was considerably lower in the case of PVA MBs. Moreover, higher droplet velocities were achieved in the case of PVA MBs at lower injection pressures.

Hydraulic flow and downstream scouring behavior on spillway system of Surumana Dam

“…Furthermore, the transition channel is expected to be in subcritical flow, and this condition is reached by adding an aerator. The critical flow at the hydraulic control point at the downstream end of the transition channel and cavitation negative pressure < -2.33 kPa or nearly -0.3 kg/cm 2 meet its requirements [10]. The test results show that the water level is still uneven in the upstream direction channel, and there is sinking flow in the QPMF, but these conditions are adequate for Q1000.…”

Kelvin-Helmholtz instability as one of the key features for fast and efficient emulsification by hydrodynamic cavitation

“…The asymmetrical collapse of the cavitation bubbles in the vicinity of the liquid–liquid interface causes the formation of intense shockwaves, micro-jets, and high intensity local microturbulences [23] , [41] , [42] , [43] . These destabilize the interface and, due to the surface energy of the collapsed bubbles being dissipated at a molecular level, enhance the mixing of immiscible liquids [31] , [41] , [42] , [43] , [44] , [68] . The larger emulsion drops that are formed during this process are additionally fragmented into smaller droplets [41] , [42] .…”

Tailoring the Icephobic Performance of Slippery Liquid-Infused Porous Surfaces through the LbL Method

“…The nanoscale thickness of the thin film and the simplicity of its application on the surface, regardless of the geometry of the substrate, are the outstanding advantages of using the LbL method for creating a stable SLIPS surfaces. Using the fluidic LbL deposition technique, we applied LbL-based SLIPS thin films inside microfluidic channels to obtain cavitating flows for biomedical and energy applications, − which is not easy to achieve by other techniques and methods.…”