Report on HEMs 2012

1. Physicomathematical
modeling of a pulse atomizer
Olga Kudryashova,
Natalya Korovina, Boris Vorozhtsov
IPCET SB RS
HEMS
2012 HEMs 2012

2. PRACTICAL USE
o Non-lethal weapon (NLW):
screening smoke, stopping
aerosols.
•
o Sedimentation of harmful solid
aerosols with preliminary
dispersion of superfine liquid
aerosols.
o Firefighting on transport.
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3. PROBLEM
Speed of the creation, superfine dispersion, autonomy.
Destruction of liquid streams: Cavitation:
Pneumatic spray: Ultrasonic nebulizer:
- TOO large particles, + Superfine,
+ HIGH speed, - LOW speed,
+ Autonomous - Demands an electricity
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4. DECISION
Cavitation gives high dispersion.
But how to create cavitation quickly?
To use energy of HEMS for creation of
cavitation and autonomy of the compressed
gas for liquid dispersion. Expected effect:
+ HIGH Speed of the creation,
+ Superfine dispersion,
+ Autonomy.
So, cavitation + dispersion by the compressed gas
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5. PREVIOUS MODEL OF ATOMIZER
The sprayer design is a
combination of a hydrodynamic
explosive tube and a centrifugal
atomizer (HEMs’2011).
+ HIGH dispersion (< 10 μm)
+ HIGH speed (< 1 sec)
+ Autonomy
Figure 1 – Scheme of an explosive-type
BUT centrifugal atomizer: the charge
chamber 1 contains an explosive
- Dangerous to use for a large charge. Gases (reaction products) push
volume of liquid. out, by means of a piston 2, water from
a container 3. Water enters into a vortex
Decision: chamber 5 through n of openings 4, and
HEMs only for cavitation + then escapes from a nozzle 6.
dispersion by the compressed gas
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6. STAGE 1: Shock wave Cavitation
γ −1  Q
pm = 
The pressure of the shock wave pm:
 ÷ ,
where  γ  V1
Zm – the amplitude of particle displacement in the
excited wave: 2Q
Zm = ,
ω – the vibration frequency, tρl S1ω 2c
Q – the explosive transformation energy,
V1 – charge chamber volume,
L – the height of the water column,
S1 – the cross-sectional area of the liquid column, Figure 2 – Scheme of an
impulse atomizer
γ – the adiabatic exponent of detonation products,
1 – compressed gas 1,
c – the wave propagation velocity in the liquid (sound 2 – liquid container,
velocity), 3 – membranes,
Z 1 2Q 4 – openings for gas,
Ml – liquid mass. Wo = m =
π
Lс M l
5 – nuzzle,
Cavitation begins at Wo>0,01 6 – pre-nuzzle volume.
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7. MOVEMENT OF CAVITATED LIQUID
A
• Abramovich-Klyachko theory: Ae =
1 + λ / 2 ( S1 / S 2 − A )
,  S  S 1
A =  1 − 1÷ 3
 S ÷ S n (1)
 2  2
• Geometrical parameter Ae (1),
1,05 2urin
where S2 – the area of entrance λ=
Re0,3
, _ Re =
ν
(2)
openings, n – their number, S3 –
 2 γ+1 
the area of nuzzle. vin =
1 2γ   pl  γ  pl  γ 
pg ρ0  ÷ −  ÷ 
 ÷  ÷ (3)
ρl S1 γ −1  p g   pg  
• The friction factor λ (2) is defined  
by speed of the incoming flow Ae =
1−ε
(4)
(3). ε3 / 2
• The effective cross-section (1 − ε) 8
tg ϕ = (5)
coefficient ε (4). (1 + 1 − ε) ε
• The spray angle φ (5). Dd −0,1
= 47,8A −0,6 ReП
−0,7
• The empirical formula for Dnuz 1 (6)
calculation of dispersion of an µ l2
П1 =
aerosol (6). Dd > 10 μm 2rnuz ρ l σ
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8. CAVITATION BUBBLES
Cavitation index:
k = Vw/Ve≈0.8, where Ve – the D13 = (1 − k ) Z m ,
3
element volume, Vw – the Figure 3 – Cavitation elements:
liquid volume. bubbles and liquid in the liquid
At the moment of outflow L(1 − k ) Q layer
D1 =
each bubble bursts into πс Ml
D4
droplets with a diameter equal
to the water layer thickness h. D2 h
L(1 − k ) D3
The expansion is considered D1 = Wo D1
2
to occur instantaneously
(adiabatic process):
 1/ γ 1/3 γ 
D1  k  p   p   a b
Dd = 3 + m ÷ -  m ÷ (7)
2  1 - k  patm   patm  
  Figure 4 – Cavitation element:
a) before outflow, b) after outflow
Dd~ 1…5 μm depending on
shock wave pressure pm
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9. CRITERIA AND DISPERSION
CHARACTERISTICS
Figure 5 – Dependence of the droplet diameter Figure 6 – Dependence of a spray angle φ on
(6) on parameters S1/S2 (1), S1/S3 (2), А (3)
1 2 1 3 parameters S1/S2 (1), S1/S3 (2), А (3)
1 2 1 3
S1/S2 – the relation of the area of section of the vortex chamber to the area of openings;
S1/S3 – the relation of the area of section of the vortex chamber to the nozzle area;
Abramovich parameter А.
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10. AEROSOL DISPERSION AND Wo
PARAMETER
To receive a high-
disperse aerosol
(diameter of drops
about 7-8 microns),
it is necessary to
create a condition
for cavitation
(Wo>0.01) but not to
allow too big pulse
impact on liquid
(Wo<0.09)
Figure 7 – Dependence of the droplet diameter on Wo:
calculated by (6) – aerodynamic mechanism (1) and by (7) –
cavitation mechanism (2)
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11. CONCLUSIONS
• The physicomathematical model of a centrifugal
pneumatic atomizer at pulse influence of HEMs is
offered.
• Expressions for calculation of the defining parameters of
atomization from input parameters of an atomizer are
received.
• It is shown that for achievement higher dispersion of an
aerosol it is necessary to provide pulse nature of impact
on liquid; the dimensionless criterion of Wo defining the
mechanism of an atomization is offered.
• The new atomizer is autonomy, gives a superfine
aerosol for a shot time.
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12. THANK YOU FOR ATTENTION
HAPPY ATOMIZING!
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