Towards a unified treatment of fully flashing sprays

Lamanna, Grazia; Kamoun, H.; Weigand, Bernhard; Steelant, Johan

doi:10.1016/j.ijmultiphaseflow.2013.08.010

Cited by 116 publications

(62 citation statements)

References 39 publications

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“…These findings are in agreement with the mechanism proposed by Lamanna et al (2014) and supported by their experimental findings, according to which a rapid liquid depressurization leads to nucleation within the orifice and uniform bubble distribution in the liquid. Furthermore, the findings of Lamanna et al (2014) demonstrated that the spray lateral spreading is controlled by the in-nozzle bubble nucleation.…”

Section: Introductionsupporting

confidence: 92%

Topology and Distinct Features of Flashing Flow in an Injector Nozzle

2016

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Section: Introductionsupporting

confidence: 92%

Topology and Distinct Features of Flashing Flow in an Injector Nozzle

2016

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“…For example, for producing a very fine spray of droplets of a uniform 30 size distribution that improve combustion efficiency (Sher et al, 2008). This is desirable in some applications such as fuel injectors (Chen et al, 2013; ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T Vetrano et al, 2013;Lamanna et al, 2014;Bohon et al, 2015;Ju et al, 2015), but also necessary when driving pressures cannot exceed certain limit (Sher et al, 2008;Zeigerson-Katz and Sher, 1998). Flashboiling atomization usually coexists simultaneously with other mechanisms of spray formation, such as turbulence, bubbles within the flow and coax-40 ial gas flows.…”

Section: Introductionmentioning

confidence: 99%

“…These values are used to estimate the boiling temperature when the ambient pressure has been reduced. If the temperature of the liquid is kept constant while varying the ambient pressure, the ratio between the ambient pressure and the vapor pressure P ∞ /P v is the leading dimensionless parameter characterizing the deviations from thermodynamic 150 equilibrium (Lamanna et al, 2014;Luo and Haidn, 2016). This pressure ratio is a key element of the chemical potential (∆µ ∼ k B T ln [P v /P ∞ ]) and it is also correlated to the rate at which vapor nuclei form (Lamanna et al, 2014;Luo and Haidn, 2016).…”

mentioning

confidence: 99%

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

Alghamdi

Thoroddsen

Hernández-Sánchez

2019

International Journal of Multiphase Flow

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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.

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“…The morphology of flashing sprays and the resulting jet angles were investigated experimentally e.g. in [1,2]. Here, the influence of the ambient temperature and pressure as well as the injection pressure were investigated for different fluids.…”

Section: Introductionmentioning

confidence: 99%

Expansion rates of bubble clusters in superheated liquids

Dietzel

Hitz

Munz

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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The present work analyses the growth of multiple bubbles in superheated liquid jets by means of direct numerical simulations (DNS). A discontinuous Galerkin approach is used to solve the Euler equations and an adequate interface resolution is ensured by applying finite-volume sub-cells in cells with interfaces. An approximate Riemann solver has been adapted to account for evaporation and provides consistency of all conserved quantities across the interface. The setup mimics conditions typical for orbital manoeuvring systems when liquid oxygen (LOX) is injected into the combustion chamber prior to ignition. The liquid oxygen will then be in a superheated state, bubble nucleation will occur and the growth of the bubbles will determine the break-up of the liquid jet. The expansion rates of bubble groups under such conditions are not known and standard models rely on single bubble assumptions. This is a first DNS study on bubble-bubble interactions in flash boiling sprays and on the effects of these interactions on the growth rates of the individual bubbles. The present simulations resolve a small section of the jet close to the nozzle exit and the growth of bubble groups inside of the jet is analysed. The results suggest that an individual bubble within the group grows more slowly than conventional models for single bubble growth would predict. The reduction in bubble growth can amount to up to 30% and depends on the distances between the bubbles and the number of bubbles within the bubble group. In the present case, the volume expansion of the superheated liquid decreases by approximately 50% if the distance between the bubbles is doubled.

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Towards a unified treatment of fully flashing sprays

Cited by 116 publications

References 39 publications

Topology and Distinct Features of Flashing Flow in an Injector Nozzle

Topology and Distinct Features of Flashing Flow in an Injector Nozzle

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

Expansion rates of bubble clusters in superheated liquids

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