General review of flashing jet studies

Polanco, Geanette; Holdo̸, A. E.; Munday, G.

doi:10.1016/j.jhazmat.2009.08.138

Cited by 107 publications

(34 citation statements)

References 60 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In this region the spray has achieved thermodynamical equilibrium and the breakup is dominated by mechanical effects (Polanco et al, 2010;Lamanna et al, 2014). There is a general agreement that flash-boiling results…”

supporting

confidence: 62%

See 1 more Smart Citation

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

Alghamdi

Thoroddsen

Hernández-Sánchez

2019

International Journal of Multiphase Flow

View full text Add to dashboard Cite

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.

show abstract

supporting

confidence: 62%

“…The main ingredient of a flash-boiling spray is a superheated liquid, phenomenon occurring when the liquid's temperature T l rises above 115 its boiling temperature T b at the ambient pressure (Polanco et al, 2010). The degree of superheating of a liquid is quantified with the temperature difference ∆T = T l −T b .…”

mentioning

confidence: 99%

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

Alghamdi

Thoroddsen

Hernández-Sánchez

2019

International Journal of Multiphase Flow

View full text Add to dashboard Cite

show abstract

“…Limitations also lie with current empirical models as they have been developed for a specific range of liquids and operating conditions [18]. Currently there is very limited computational work available in the literature that has discussed methods for successfully modelling multi-hole flashing sprays under engine-like conditions, as well as capturing the mechanism of spray collapse that can lead to quite complex spray structures and affect the in-cylinder mixture formation.…”

Section: Present Contributionmentioning

confidence: 99%

Aspects of Numerical Modelling of Flash-Boiling Fuel Sprays

Price¹,

Hamzehloo²,

Aleiferis³

et al. 2015

SAE Technical Paper Series

View full text Add to dashboard Cite

Flash-boiling of sprays may occur when a superheated liquid is discharged into an ambient environment with lower pressure than its saturation pressure. Such conditions normally exist in direct-injection spark-ignition engines operating at low incylinder pressures and/or high fuel temperatures. The addition of novel high volatile additives/fuels may also promote flashboiling. Fuel flashing plays a significant role in mixture formation by promoting faster breakup and higher fuel evaporation rates compared to non-flashing conditions. Therefore, fundamental understanding of the characteristics of flashing sprays is necessary for the development of more efficient mixture formation. The present computational work focuses on modelling flash-boiling of n-Pentane and isoOctane sprays using a Lagrangian particle tracking technique. First an evaporation model for superheated droplets is implemented within the computational framework of STAR-CD, along with a full set of temperature dependent fuel properties. Then the computational tool is used to model the injection of flashing sprays through a six-hole asymmetric injector. The computational results are validated against optical experimental data obtained previously with the same injector by high-speed imaging techniques. The effects of ambient pressure (0.5 and 1.0 bar) and fuel temperature (20-180° C) on the non-flashing and flashing characteristics are examined. Effects of initial droplet size and break-up submodels are also investigated. The computational methodology is able to reproduce important physical characteristics of flashboiling sprays like the onset and extent of spray collapse. Based on the current observations, further improvements to the mathematical methodology used for the flash-boiling model are proposed.

show abstract

“…Most importantly it depends on the inlet temperature and difference between internal and external pressure. Experiments were done using photography technique, Laser Doppler anemometry, in the past but failed to explain properly the phenomenon behind such complex flows (Polanco et al [7]). There have been a few attempts to model such two-phase flows inside a nozzle numerically but they were mainly limited to one-dimensional flow (Barret et al [8]).…”

Section: Introductionmentioning

confidence: 99%

“…There have been a few attempts to model such two-phase flows inside a nozzle numerically but they were mainly limited to one-dimensional flow (Barret et al [8]). Though superheated jets have been studied adequately in the past but fundamental understanding of the physics behind such non-equilibrium twophase flow is still an open problem (Polanco et al [7]). Moreover experimental data is not easy to obtain due to the complex nature of the flow and high pressure and temperature involved.…”

Section: Introductionmentioning

confidence: 99%

Internal and external characteristics of a superheated jet

Sinha¹,

Balasubramanian²,

Gopalakrishanan³

2015

Computational Methods in Multiphase Flow VIII

View full text Add to dashboard Cite

Flashing phenomenon occurs by rapid release of sub cooled/saturated liquid into a medium with lower pressure. This creates an expansion associated with vapour formation. The thermodynamic instability causes breakup of the liquid jet. Understanding the physics behind the jet disintegration and flashing phenomenon is still an open problem, with applications in automotive and aerocombustor industry. The behaviour of a flashing jet is highly dependent on the input parameters, most importantly inlet temperature and pressure. In the present study, the external (outside nozzle) and the internal (inside nozzle) flow characteristics of the two-phase flow has been studied numerically and experimentally. The phase change from liquid to vapour takes place over a finite period of time. Homogenous Relaxation Model (HRM) is used to model such finite rate process. In order to validate the numerical results, controlled experiments were carried out. Results revealed that the mass flow rate obtained numerically matches with that of experiments. Optical diagnostics were used to study the flow characteristics. Flow characteristics in terms of spray angle, penetration depth will be obtained from the experiments for better understanding of the break-up mechanism involved.

show abstract

General review of flashing jet studies

Cited by 107 publications

References 60 publications

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

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

Aspects of Numerical Modelling of Flash-Boiling Fuel Sprays

Internal and external characteristics of a superheated jet

Contact Info

Product

Resources

About