Ultra-high speed visualization of a flash-boiling jet in a low-pressure environment

Abstract

Highlights• We visualized flash-boiling jets at an unprecedented frame rate of 5 Million frames per second. At such high frame rate we observed for the first time the evolution of the bubble expansion and the burst mechanisms, responsible for the jet atomization.• For developed flash-boiling conditions, minimum pixel intensity profiles revealed that droplets are ejected in all directions from the nozzle. This crucial fact was translated into spray angles larger than 300• .• The detailed close up to the nozzle revealed that the droplet size distribution of the spray is wide, contrary to the common belief. Using a simple argument we infer that the smallest droplets are on the hundreds of nanometer range. This means that the drop size distribution extends trough almost four orders of magnitude.• We measured velocities up to 140 m/s during the expansion of bubbles from the core of the jet. Such velocity is a bit less than half of the speed of a 0.22 bullet, an unprecedented velocity for expanding bubbles. AbstractWe visualize the flash-boiling atomization of liquid jets released into a low-pressure environment at frame rates of up to five million frames per second using a long distance microscope. Such temporal resolution allowed us to capture the details of the bubble expansion mechanism, responsible for the jet atomization, for the first time. We document an abrupt transition from a laminar to a fully external flashing jet by systematically reducing the ambient pressure. We perform experiments with different volatile liquids, ejected through micro-nozzles with different inner diameters. Surprisingly, minimum pixel intensity projections revealed spray angles close to θ s ∼ 360• and speeds of bubble expansion up to 140 m/s. Particle tracking shows that ejected droplets achieve speeds much larger than the jet velocity and drop sizes order of magnitude smaller than the diameter of the nozzle. Furthermore, hole growth speeds measured on the bubbles film in combination with to Taylor-Culick predictions suggests that the smallest droplet sizes are on the hundreds of nanometer or submicron range, which contravenes the general belief that flash-boiling atomization results in uniform drop sizes.

Jet breakup in superfluid and normal liquid He4

“…Contracting liquid filaments breakup in a similar manner to Rayleigh jets, forming one to multiple droplets of various sizes depending on Oh l and the aspect ratio [22,[34][35][36][37]. Other topics include: the forced breakup from sinusoidal perturbations [38][39][40], inkjet printing [41], liquid jets with surrounding coaxial gas flow [42], computer modeling [43,44], jet impact on solids [15,45] and liquids [46][47][48][49], flash boiling breakup when a jet injects into an atmosphere below its own vapor pressure [50,51], cooling and fragmentation of molten metal jets [52,53], and applications such as fuel injection [54,55] and other technologies [56]. At sufficiently low flow rates, jets do not form resulting in only dripping, which has also been extensively studied [57][58][59][60][61] including the transition from dripping to jetting [29,30].…”

An analysis of surface breakup induced by laser-generated cavitation bubbles in a turbulent liquid jet

“…The breakup of the liquid jet in effervescent atomization usually has a radial distribution along the jet axis, while for cavitation bubble-induced breakup, the breakup basically goes along the cross-flow direction (Robert et al 2007). Another relevant condition comes from a recent study of the breakup of a flash-boiling jet in a low pressure environment (Alghamdi et al 2019). By systematically controlling the ambient pressure, nucleation and expansion of single bubbles and bubble burst-induced breakup of the jet were observed with an ultra-high speed imaging setup.…”

Evaluation of Motion Blur in High-Speed Neutron Imaging at Kyoto University Research Reactor

“…Usually, optical imaging technique using a high-speed camera has been applied to rapid flow observation. Very fast imaging (>1,000,000fps) can be performed using the high-speed camera [1] and the bubble shape and motion in bubbly flow can be detected easily. However, it is difficult to measure the flow behavior inside metal vessel which is generally used in the experiments at high temperature and high pressure conditions.…”