A two-fluid atomizer was used to study the breakup of liquid-nitrogen jets in nitrogen, argon, and helium atomizing gas flows. A scattered-light scanner particle sizing instrument previously developed at NASA Lewis Research Center was further developed and used to determine characteristic drop diameters for the cryogenic sprays. In the breakup regime of aerodynamic-stripping, i.e., sonic-velocity conditions, the following correlation of the reciprocal Sauter mean diameter, D(sub 32)exp -1, with the atomizing-gas flowrate, W(g), was obtained: D(sub 32)exp -1 = k(sub c)(W(g)exp 1.33), where k(sub c) is a proportionality constant evaluated for each atomizing gas. Values of k(sub c) = 120, 220, and 1100 were obtained for argon, nitrogen, and helium gasflows, respectively. The reciprocal Sauter mean diameter and gas flowrate have the units of 1/cm and g/sec, respectively. In the regime of capillary-wave breakup, or subsonic conditions, it was found that D(sub 32)exp -1 = k(g)(W(g)exp 0.75), where k = 270, 390, and 880 for argon, nitrogen, and helium gasflows, respectively

Ingebo, Robert D.

English

NASA Technical Reports Server

NASA Technical Memorandum_ 103734 .....
......./6J6 ......
O>_,_ -
Cryogenic Liquid-Jet Breakup
in Two-Fluid Atomizers
(_ASA-TM-IO3734) CRYOGENIC LIQUID-JET
BREAKUP IN TWO-_LUI_ ATOMIZERS (NASA) b p
CSCL 200
NOI-19402
Uncles
. G3/35 0001070
Robert D. Ingebo
Lewis Research Center
Cleveland, Ohio
Prepared for the
Fifth International Conference on Liquid Atomization and Spray Systems
sponsored by the National Institute of Standards and Technology
Gaithersburg, Maryland, July 15-18, 1991
tXl/_A
i
https://ntrs.nasa.gov/search.jsp?R=19910010089 2020-03-19T18:43:01+00:00Z
t
CRYOGENIC LIQUIO-IET BREAKUP IN TWO-FLUID ATOMIZERS
Robert D. lngebo
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
ABSTRACT
A two-fluid atomizer was used to study the
breakup of liquid-nitrogen jets in nitrogen, argon
and helium atomizing-gas flows. A scattered-light
scanner particle sizing instrument previously
developed at NASA Lewis Research Center was further
developed and used to determine characteristic drop
diameters for the cryogenic sprays. In the breakup
regime of aerodynamic-stripping, i.e., sonic-
velocity conditions, the following correlation of
the reciprocal Sauter mean diameter, D_] , with the
atomizing-gas flowrate, W , was obtaine_:
g
D-132 " kcW1.33g , where k c is a proportionality con-
stant evaluated for each atomizing gas. Values of
k c = 120, 220 and 1100 were obtained for argon,
nitrogen and helium gasflows respectively. The
reciprocal Sauter mean diameter D_ and gas flow-
rate W , have the units of cm-1 and g/sec,
' g
respecttvely.
In the regime of capillary-wave breakup, or
subsonic conditions, it was found that;
Dz_ - k W0.75, where k = 270, 390 and 880 for
_a g _
argon, nilrogen and helium gasflows, respectively.
INTRODUCTION
The drop size of disintegrating liquid jets in
low velocity airflow is controlled primarily by a
capillary-wave mechanism and characteristic parti-
cle size is generally relatively large. However
when a liquid jet is injected into high velocity or
sonic flows, an aerodynamic stripping mechanism
occurs in which the jet is disintegrated into a
large number of small liquid particles, thereby
producing a large liquid surface area. In this
case, disintegration occurs before waves have time
to form on the liquid-jet surface. The emphasis
of the present study was on the mechanism of
aerodynamic-stripping, in which two-fluid nozzles
were used to impact liquid-nitrogen jets with
argon, nitrogen and helium atomizing-gas flows.
Cryogenic liquid-jets with atomizing-gas flows
injected into rocket combustors are quickly disin-
tegrated into small-droplet sprays. In order to
calculate vaporization or burning rates, it is nec-
essary to characterize the spray in terms of drop
size distribution and mean drop size such as the
Sauter mean diameter. Once characteristic drop
sizes are known, mathematical expressions can be
derived to adequately describe a two-fluid atomiza-
tion process in which various liquid propellants
and atomizing-gas combinations are used to enhance
spray combustion and yield high combustor perform-
ance over a wide range of operating conditions.
Knowledge of the characteristic size of drops
in sprays are also needed in experimental studies
of fuel-spray combustion in diesel and other inter-
nal combustion engines and gas turbine combustors.
In addition, knowledge of water sprays is needed to
study the formation of ice on airfoils in icing
wind tunnel experiments. In the task of character-
izing sprays, detailed knowledge of the mechanics
of liquid-jet disintegration is especially needed
at the point of initial spray formation close to
the atomizer orifice. This is especially true in
the study of highly volatile cryogenic liquids.
From this knowledge, accurate initial conditions
can be established for modeling a fuel spray com-
bustion process or modelling the process of ice
formation on airfoils.
Numerous investigators have obtained experi-
mental drop size data and correlated it with rela-
tive velocity, i.e., gas velocity relative to
liquid velocity and also with liquid properties, as
given in Refs. 1 to 7. Some of the correlations do
not agree very well with atomization theory; which
is generally at)ribut(d to the fact that measure-
ment techniques and drop sizing instruments have
yet to be developed and standardized to the extent
that good agreement might be expected. The fluid
property having the greatest effect on the drop
size of sprays produced with two-fluid nozzles is
the gas velocity. Although numerous investigators
have studied this phenomena, the effect of gas mass
flux on the drop size of cryogenic sprays has not
been established in the spray literature. There-
fore, the main objective of the present study was
to determine the effect of atomizing-gas mass flux
on liquid-nitrogen spray characteristics.
Prior to the present study, an investigation
of water sprays was made with two-fluid nozzles and
good agreement of experimental results with atomi-
zation theory was obtained, as discussed in Ref. 1.
It was found that the Sauter mean diameter, D32,
could be correlated with nitrogen gas flowrate, Wn,
raised to the -1.33 power, which agrees well with
theoretical expressions for liquid jet breakup in
high velocity gasflow. As a continuation of this
study, the present investigation was initiated to
extend experimental conditions to include cryogenic-
liquid-jet breakup in helium, argon, and nitrogen
gas flows.
Two-phase flow in which transfer of momentum
from low velocity and sonic gasflows to the surface
of liquid-nitrogen jets was experimentally investi-
gated by using three different atomizing gases to
produce clouds of liquid-nitrogen droplets. Tests
were conducted in the capillary-wave and
aerodynamic-stripping regimes of disintegrating
liquid jets. A scattered-light scanning instrument
developed at NASA Lewis Research Center was used to
measure characteristic drop diameters of the
cryogenic-liquid sprays. By correcting for gas
turbulence and thermal gradient effects on measure-
ments, reproducible data was obtained with the
scattered-light scanner. To avoid the loss of
small liquid-nitrogen droplets due to their high
vaporization rate, measurements were taken close to
the nozzle orifice. The entire spray cross section
was sampled with a 4.4 by 1.9 cm rectangular laser
beam, at an axial distance of 1.3 cm downstream of
the atomizer.
APPARATUS AND PROCEDURE
A two-fluid nozzle was mounted in the test
section as shown in Fig. 1, which also shows the
optical path of the scattered-light scanner. Air
supplied at ambient temperature, 293 K, passed
through the 15.24 cm inside diameter test section
and exhausted to the atmosphere. The test section
was 1 m in length and a 5.08 cm diameter orifice
was used to measure the air flowrate in the test
section. A flow of dry air at a velocity of
5 m/sec was maintained in the test section to aid
in transporting small droplets through the laser
beam. This prevented ambient humid air from con-
tacting the spray and thereby avoided the formation
of ice particles in the laser beam.
A detailed diagram of the two-fluid nozzle is
shown in Fig. 2. It was mounted in the center of
the test section and operated over pressure ranges
of 0.2 to 1.0 MPa for both liquid nitrogen and the
atomizing gases. Liquid nitrogen sprays were
injected downstream into the airflow just upstream
of the duct exit. The spray was sampled at a
distance of 1.3 cm downstream of the atomizer
orifice with a 4.4 by 1.9 cm rectangular laser
beam produced by the 0.01 cm diam aperture shown
in Fig. 1.
Liquid nitrogen, LN2, at a temperature of 77 K
measured with an [.C. thermocouple, was axially
injected into the airstream at a flowrate of
27.5 g/sec, as indicated by a turbine flow meter.
The atomizing gas was then turned on to break up
the LN2 jet and weight flow rate was measured with
a 0.51 cm diameter sharp-edge orifice. After the
air, atomizing-gas and LN2 flow rates were set,
characteristic drop diameters were determined from
measurements made with the scattered-light scanner.
The optical system of the scattered-light
scanner is shown in Fig. 1. The instrument meas-
ures scattered-light as a function of scattering
angle by repeatedly sweeping a variable-length slit
in the focal plane of the collecting lens. The
data obtained is scattered-light energy as a
function of the scattering angle relative to the
laser-beam axis. This method of particle size
measurement is similar to that given in Ref. 8 and
it is described in detail in Ref. 9. Calibration
was accomplished with five sets of monosized poly-
styrene spheres having diameters of 8, 12, 25, 50
and 100 }_m. Since the sprays were sampled very
close to the atomizer orifice, they contained a
relatively high number of very small drops. As a
-- 58 CM
FIGURE I. ATP_SPII['RIC PRESSURE TEST SECTION AND OPTICAL PATII OF SCATTERED-LIGHT SCANNER.
INSIDE
NITROGEN DIAMETER
GAS -,. 0.56q CM--x
; ----==T_.,._ .
...................q
L LlgtllD NITRODEN DIAP£TER
I
0.663 CM J
FIGORE 2. - DIAGRAM OF pNEUMATIC TWO-FLUID ATOMIZER.
ORIGINAL PAGE IS
OF POOR QUALITY
3.3
5.06 7
i 10.0
i 12,5
1G.7
20.0
25.0
53,3
d 3OOO
-- 2000
T
• 1000
6oo
50'0
- qO0
-- 300
ATORI Z [ NG-G._S
0 NITRO6EN
A ARGON
-- 0 ¢
.3 .q .L_ .I; .81+0 1.5 2 3 q 5 6 7 8 910
ATOt4IZ[NG-GAS FLO'_ATE, g/see
FIGURE 3. - CO_RELAT[ON OF SAU]_R MEAN DIARETER WITH ATOM]TING-6AS FLONRATE.
result, the light-scattering measurements required
correction for multiple scattering as described in
Refs. 9 and 10 for the case of high concentrations
of droplets_ Drop size measurements were also
corrected as described in Ref. 9 to include Mie
scattering theory when very small characteristic
droplet diameters, i.e., <10 tim,were measured.
Atomizing-gas temperatures were approximately
293 K and surface temperatures of the liquid-
nitrogen jets were always near the boiling point of
liquid-nitrogen, i.e., approximately 77 K. This
created large temperature gradients that deflected
the laser beam and caused beam steering to occur.
However, by carefully adjusting the laser beam away
from the slit in the scattered-light scanner opti-
cal system, the effect of beam steering on measure-
ments was negligible.
EXPERIMENTAL RESULTS
As shown in Fig. 1, the entire spray cross
section was sampled at an axial distance of
= 1.3 cm downstream of the two-fluid atomizer
orifice. Values of the Sauter mean diameter, D32,
and reciprocal SMD, O_ , are plotted against
atomizing-gas flowrate as shown in Fig. 3. Tests
were conducted over a relatively wide range of
atomizing-gas flowrates that included both sub-
sonic and sonic gas-velocity conditions.
At relatively low or subsonic atomizing-gas
flow conditions, breakup of the LN2 jets occurred
primarily in the capillary-wave regime of atomiza-
tion and the following general correlation of D_
with gas flowrate, Wg, was obtained:
-1 = k W°'75
D32 g g
where the reciprocal $MD and gas flowrate are
expressed as cm-1 and g/sec, respectively. The
correlating constant k_ = 270, 390 and 880 when
argon, nitrogen and helium, respectively, were used
to atomize the LN2 jets. The exponent 0.75 for Wg
is approximately 10 percent higher than the 2/3
exponent given for gas velocity in the theoretical
expression reported in Ref. 11.
In regime of aerodynamic-stripping or sonic-
velocity atomizing-gas flow conditions, the follow-
ing expression was obtained:
-1 = k W1"33
D32 c g
where the correlating constant kc = 110, 220 and
1100 when argon, nitrogen and helium, respectively
were used as atomizing gases. The exponent 1.33
for Wg is the same at the 4/3 exponent given for
gas veIocity in Ref. 11. Thus, good agreement with
atomization theory was obtained in the regime of
aerodynamic stripping conditions.
Transition from the regime of capillary-wave
breakup to that of aerodynamic-stripping occurred
at values of D_ - 700 am-1 or D32 -j5 }_m,
Table 1 Proportionality constant, k, and gas flowrate
exponent, x, for correlating expression:
-I = k Wx
D32 g
Breakup regime Argon Nitrogen Helium
Capillary-wave:
kg, constant 120 220 1100
x, exponent 0.75 0.75 0.75
Aerodynamic-stripping:
kc , constant 270 390 880
x, exponent 1.33 1.33 1.33
3
approximately, for the atomizing gases used in the
present study. Values of k c and kg are given
in Table 1.
CONCLUD[NG REMARKS
The fluid mechanics of liquid-nitrogen jet
breakup is much more difficult to study than the
atomization of fuel or water jets. This is primar-
ily due to the fact that surface temperatures of
the liquid-nitrogen jets used in the present study
were always near the boiling point of liquid nitro-
gen, i.e., approximately 77 K. Since the atomizing
gases were at room temperature, approximately
293 K, this created large temperature gradients
that deflected the laser beam and caused beam
steering to occur as characteristic drop diameter
was measured with the scattered-light scanner.
This problem was minimized in the present investi-
gation by moving the laser beam away from the slit
in the scattered-light scanner optical system.
REFERENCES
1. Ingebo, R.D., "Experimental and Theoretical
Effects of Nitrogen Gas Flowrate on Liquid-Jet
Atomization," Journal of Propulsion and Power,
Vol. 4, No. 6, Nov.-Dec., 1988, pp. 406-411.
2. Kim, K.Y. and Marshall, W.R., Jr., "Drop Size
Distributions from Pneumatic Atomizers," AIChE
Journal, Vol. 17, No. 3, May 1971, pp. 575-584.
3. Lorenzetto, G.E. and Lefebvre, A.H., "Measure-
ments of Drop Size on a Plain Jet Airblast
Atomizer," AIAA lournal, Vol. 15, No. 7, July
1977, pp. 1006-1010.
4. Nukiyama, S. and Tanasawa, Y., "Experiments on
the Atomization of Liquids by Means of a Air
Stream, Parts Ill-IV," Transactions of the
Society of Mechan!cal Engineers_ Japan, Vol. 5,
No. 18, Feb. 1939, pp. 63-75.
5. Weiss, M.A. and Worsham, C.H., "Atomization in
High Velocity Airstreams," American Rocket
Society Journal, Vol. 29, No. 4, Apr. 1959,
pp. 252-259.
9.
10.
11.
Wolf, H.E. and Andersen, W.H., "Aerodynamic
Break-up of Liquid Drops," Proceedings of the
5th International Shock Tube Symposia,
Z.I. Slawasky, J.F. Moultin, Jr., and
W.S. Filler, eds., Naval Ordnance Lab., White
Oak, MB, 1965, pp. 1145-1169. {Avail. NTIS,
AD-638011.)
Ingebo, R.D., "Fuel Spray Simulation With Two-
Fluid Nozzles," AIAA Paper 89-0053, July 1989
(also, NASA TM-101367, 1988).
Swithenbank, J., Beer, [.M., Taylor, D.S.,
Abbot, D., and McCreath, G.C., "A Laser
Diagnostic Technique for the Measurement of
Droplet and Particle Size Distribution," in
Experimental Diagnostics in Gas Phase
Combustion Systems," B.T. Zinn and
G.T. Boulman, eds., Progress in Astronautics
and Aeronautics, Vol. 53, AIAA, New York,
1977, pp. 421-447.
Buchele, D.R., "Particle Sizing by Weighted
Measurements of Scattered Light," NASA
TM-100968.
Felton, P.G., Hamidi, A.A., and Aigail, A.K.,
"Measurement of Drop Size Distribution in Dense
Sprays by Laser Diffraction," in ICLASS-85:
Proceedings of the Third International Con-
ference on Liquid Atomisation and Spray
Systems, P. Eisenklam and A. Yule, eds.,
Institute of Energy, London, 1985, Vo[. 2,
pp. IVA/4/1-IVA/4/11.
Adelberg, M., "Mean Drop Size Resulting from
the Injecti6n of a'Liquid Jet Into a High-
Speed Gas Stream," AIAA Journal, Vol. 6, June
1968, pp. 1143-1147.
4
I_A Report Documentation PageNational Aeronauticsand
Space Adminislration
1. Report No.
NASA TM- 103734
2. Government Accession No,
4. Title and Subtitle
Cryogenic Liquid-Jet Breakup in Two-Fluid Atomizers
7. Author(s)
Robert D. Ingebo
9, Performing Organization Name and Address
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191
12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, D.C. 20546-0001
3. Recipient's Catalog No.
5, Report Date
6. Performing Organization Code
'= 8. Performing Organization Report No.
E-5854
10, Work Unit No.
505-62-52
11. Contract or Grant No.
13. Type of Report and Period Covered
Technical Memorandum
14. Sponsoring Agency Code
15. Supplementary Notes
Prepared for the Fifth International Conference on Liquid Atomization and Spray Systems sponsored by the
National Institute of Standards and Technology, Gaithersburg, Maryhmd, July 15-18, 1991. Responsible person,
Robert D. Ingcbo, (216) 433-3586.
16. Abstract
A two-fluid atomizer was used to study the breakup of liquid-nitrogen jets in nitrogen, argon and helium atomizing-
gas flows. A scattered-light scanner particle sizing instrument previously developed at NASA Lewis Research
Center was further developed and used to dctcrmine characteristic drop diameters for the cryogenic sprays. In the
breakup regime of aerodynamic-stripping, i.e., sonic-velocity conditions, the following correlation of the reciprocal
• = k W 1.33 where k_ is aSauter mean diameter, D._ 1 with the atomizing-gas flowrate, Wg, was obtained: D3-jm ..,..g ,
proportionality constant evaluated for each atomizing gas. Values of k_ = 120, 220 and 1100 were obtained for
argon, nitrogen and helium gasflows respectively. The reciprocal Sauter mean diameter D_ I and gas flowrafe,
Wg, have the units of cm-I and g/see, respectively. In the regime of capillary-wave breakup, or subsonic
conditions, it was found that; D_ I = kgW_ 75, where k = 270, 390, and 880 for argon, nitrogen and helium
gas flows, respectively.
17. Key Words (Suggested by Author(s))
Cryogenic liquids; Sprays; Particle size, multi-phase
flow; Light scattering instruments; Sauter mean diameter
18. Distribution Statement
Unclassified- Unlimited
Subject Category 35
19. SecurityClassif. (of this report) 120. SecurityClassif. (of thispage) j21. No, of pages 22, Price"
Unclassified [ Unclassified ] 6 A02
NASAFORM1626OOT86 *For sale by the National Technical Information Service, Springfield, Virginia 22161
t_=I_IMENlr,10#/_II¥ _ PRECEDING PAGE BLANK NOT FILMED



Cryogenic liquid-jet breakup in two-fluid atomizers

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server