This paper presents a characterization of flow-blurring (FB) and flow-focusing (FF) modes of atomization using a new atomizer, which enables continuous transition from FB to FF regimes by controlling the recess of a liquid tube. The atomizer has optical access and features flexibility in controlling the Weber number (We) and the air/liquid mass flow ratio (ALR). The Phase Doppler Particle Analyzer (PDPA) technique is employed here along with long-distance microscopic and direct imaging to observe and characterize the atomization regime. Experiments were carried out with water and air as the working fluids at room temperature and in an atmospheric pressure environment. The results show that operation in the FB regime generates smaller droplet sizes in the spray core compared to the FF regime. However, the benefit of FB decays with increasing We, and eventually the difference between both regimes decreases. Among the distinctive features of FB sprays found only in the near-field region are: a more noticeable change in the mean droplet size with the radial direction, more pronounced polydispersity, larger centerline axial velocity and larger axial and radial velocity fluctuations. Liquid tube recess was also found to be an important parameter in controlling the spray behavior in the FB regime. It was found to impact the droplet size, the values and shape of the axial velocity variation curves, as well as the range of radial velocity values. It is also shown that, at a high enough We, effective differentiation between FB and FF atomization regimes became harder and rather limited to the visual confirmation of the presence of a bubble in the liquid tube.
This
review summarizes the state of the art of flow blurring atomization,
focusing both on fundamental aspects of this atomization mode as well
as key observations made from applications of flow blurring. Flow
blurring is an internal-twin fluid atomization method that offers
effective interphase turbulent mixing and very fine liquid sprays.
The features of this mode of liquid breakup make it attractive for
applications in liquid fuel spray combustion, although it also offers
potential benefits to applications requiring the atomization of non-Newtonian
liquids, for example, such as in polymer filament manufacturing. This
review concisely covers features of the internal nozzle flow of flow
blurring atomizers, the effect of the orifice geometry on the spray,
the behavior of the near-field spray region, the effect of liquid
physical properties on droplet behavior, and general observations
of reacting flow blurring sprays. Consistencies among the various
research conducted is highlighted throughout the review, and this
information, along with identified gaps in our understanding, is used
to offer suggestions for future research.
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