Droplet Dynamics In Internally Mixed
Twin-fluid Spray
Author(s)
J. Jedelsky & M. Jicha
Abstract
Effervescent atomizers are based on the mixing of gas with liquid prior to
discharge. We describe the discharge of a two-phase mixture and movement of
droplets in a gas jet using simple theoretical models, following with elucidation
of droplets dynamics using experimental data for an effervescent spray.
Discharge of the liquid-gas mixture from the nozzle is solved using a
combination of two discharge models. Depending on operation conditions, 59–
64% of the total discharged mass corresponds to the Separated Flow Model and
the rest to the Homogeneous Flow Model. Discharge velocity of the liquid is 12–
27% of the gas exit velocity. The liquid-gas velocity ratio is negatively
correlated with gas-to-liquid mass ratio (GLR) and positively correlated with
inlet pressure. Radial profiles of axial droplet velocity, as measured using Phase
Doppler anemometry, are axisymmetric bell-shaped with a maximum in the
centreline analogous to the profile defined for a simple gas jet which, however, is
more flat near the centreline and declines much faster for higher radial positions.
Mean velocity in individual spray positions varies with particle size within a
range of several m/s typically. This variation is closely related to particle Stokes
number, Stk. Variation of mean velocity with operation pressure and GLR can be
explained with discharge conditions; higher pressures and GLRs lead to higher
discharge velocities that are reflected in the spray downstream. Stokes numbers
are generally << 1 for particle sizes Dd up to 10 μm so these particles smoothly
follow the gas flow. Stk for sizes 10 μm < Dd < 50 μm depends on flow regime
and position in the spray and can be found typically within 0.1 < Stk < 10.
Particles with Dd ≥ 100 μm have usually Stk > 10 and very weakly interact with
the gas.
Keywords: droplet dynamics, internal mixing, twin-fluid spray, effervescent
atomization, Stokes number, velocity field, dispersed two-phase flow.
Keywords
droplet dynamics, internal mixing, twin-fluid spray, effervescent
atomization, Stokes number, velocity field, dispersed two-phase flow.
Related Book
Other papers in this volume
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