A comprehensive theoretical framework of deposition from combustion gases was developed covering the spectrum of various mass delivery mechanisms including vapor, thermophoretically enhanced small particle, and inertially impacting large particle deposition. Rational yet simple correlations were provided to facilitate engineering surface arrival rate predictions. Experimental verification of the deposition theory was validated using burner rigs. Toward this end, a Mach 0.3 burner rig apparatus was designed to measure deposition rates from salt-seeded combustion gases on an internally cooled cylindrical collector

Gokoglu, S. A.

English

NASA Technical Reports Server

N87-11192
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EXPERIMENTAL VERIFICATION OF VAPOR DEPOSITION MODEL IN MACH 0.3 BURNER RIGS*
S_leyman A. G6ko_lu
Analex Corporation
Gas turbine failures associated with accelerated "hot" corrosion moti-
vated this research intended to obtain a better understanding of the deposi-
tion phenomenon of corrosive species on turbine blades. A comprehensive yet
tractable theoretical framework of deposition from combustion gases has been
developed covering the spectrum of various mass delivery mechanisms including
vapor (refs. 1 and 2), thermophoretlcally enhanced small particle (ref. 3),
and Inertlally impacting large particle (ref. 4) deposition. Rational yet
simple correlations have been provided to facilitate engineering surface
arrival rate predictions (refs. 5 to 7). The objective of the program at the
NASA Lewis Research Center has been the experimental verification of the depo-
sition theory using burner rigs. Toward this end, a Mach 0.3 burner rig
apparatus has been designed to measure deposition rates from salt-seeded com-
bustion gases on an internally cooled cylindrical collector (ref. 8).
The results of the previous experiments have been reported in detail in
reference 8. Different sodium salt solutions (e.g., NaCl, sea salt, NaNO 3,
and Na2S04) were sprayed into the combustor; however, in all cases the
expected deposit was Na2SO 4. Indeed, the X-ray analysis of the deposit
verified this prediction. There were two regions of disagreement between the
deposition rate prediction of the chemically frozen boundary layer (CFBL)
vapor deposition theory and the experimentally observed deposition rates of
Na2SO 4, depending on whether the collector temperature was above or below
the melting point of Na2SO 4. The discrepancy for collector temperatures
above the melting point of the deposit is attributed to the shear-drlven mol-
ten deposit layer run off from the smooth collector surface (ref. 9). How-
ever, for collector temperatures below the melting point of the deposit the
results were puzzling. Although both the theory and the experiments showed
plateau deposition rate behavior, the disagreement level depended on the
sodium salt sprayed, ranging from good agreement for NaCl seeded experiments
to almost three times the predicted deposition rate for Na2SO 4 seeded
experiments.
As a first attempt to analyze the experimental system more carefully and
systematically, droplet sizes were determined from the salt solution probe
using a Malvern partlcle/droplet size analyzer as a function of atomizing air
pressure and solution composition for different probes. Based on the droplet
sizes obtained, vaporization time calculations of the droplets during their
residence times inside the combustor showed that droplets survived and were,
in fact, large enough to impact inertlally on the collector. Deposition rate
predictions for Na2SO 4 seeded experiments based on the particle inertial
Impactlon theory agreed well with the experimental observations. A particle
capture test was designed to verify experimentally the theoretical prediction
of the presence of particles in the previous experiments. Indeed, SEM
*Work done under NASA contract NAS3-23293 at the Lewis Research Center.
II0
https://ntrs.nasa.gov/search.jsp?R=19870001759 2020-03-23T15:02:31+00:00Z
photographs of the deposits collected on targets in a few seconds at the orig-
inal collector location show the particles very clearly even for NaCl seeded
flames (ref. lO). Therefore, the agreement between the CFBL vapor deposition
theory and the previous NaCl seeded experiments was coincidental, the arrival
rate by particle inertial impactlon mechanism giving the same rate as one
would expect from vapor convective-diffuslon mechanism. Moreover, the chemi-
cal analysis of the deposit collected in about 5 sec in particle capture tests
for a NaCl seeded flame showed about 80 percent NaCl and 20 percent Na2SO 4
by weight. This indicates that NaCl particles of l to 5 _m size range are
able to react chemically and convert to Na2SO 4 on the collector in such
short durations. The fact that only Na2SO 4 was observed in X-ray analysis
of the deposits for all sodium salts seeded is explained by the fast reaction
times of small (l to 5 _m) sodium salt particles to convert to Na2SO 4 as
compared with the deposition run times of 30 min. Only those particles that
deposited during the last few seconds of the experiment had no time to react
and, therefore, were able to preserve their identity. However, their concen-
tration was too low to be detected by X-ray analysis.
When predicting vapor deposition rates the CFBL theory makes use of the
"cyllnder-ln-crossflow" assumption in estimating the average mass transfer
coefficient (Nusselt number). This assumption needed to be checked, because
our cylindrical collector diameter (3/4 in) is not small compared with the jet
stream diameter from the burner rig nozzle exit (l in). Indeed, under typical
experimental conditions there is about 250° to 300 ° C difference in tempera-
ture between the forward and the backward stagnation point of the stationary
collector (ref. lO), which invalidates the "cylinder-ln-crossflow" assump-
tion. In order to regain a correct predictive capability of vapor deposition
rates, even if there were no particles present, an experimentally determined
mass transfer Nusselt number has to be supplied to the theory.
Having determined the problematic features of the previous experiments
and having been able to interpret the previous results to our sufficient
satisfaction, new experiments and procedures have been designed as remedies.
In order to eliminate the presence of particles two possible routes are being
taken: (1) Na dispersions in light oll or mineral spirits which are both
soluble in Jet A-l fuel will be used, or (2) alcohol will be used as fuel, and
Na acetate (Na source) and thlourea (S source) will be dissolved in it to
desired concentrations. The predictions based on (1) the experimentally
determined droplet size distributions of the fuel nozzles used in our experi-
ments, (2) Na particle size in the dispersions, and (3) the longer residence
times of the droplets in the combustor show that both methods are feasible and
complete vaporization (burning) should be attained.
The naphthalene sublimation technique (ref. II) will be used at room tem-
perature for the cylindrical collectors to determine the average mass transfer
coefficient as a function of the Reynolds number in our experimental configu-
ration. This technique is superior to the previously tried calorimetry tech-
nique in eliminating the temperature gradients that inevitably exist in our
experiments. Another approach that will provide a predictive capability is to
use a simpler collector geometry. For that purpose only a segment which is
20° on both sides of the forward stagnation point of our previous cylindrical
targets will be used as the collection (deposition) surface. In this way, the
stagnation region mass transfer will be studied simulating the nose region of
blades.
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REFERENCES
Rosner, Daniel E., et al.: Chemically Frozen Multlcomponent Boundary
Layer Theory of Salt and/or Ash Deposition Rates from Combustion Gases.
Combust. Sci. Technol., vol. 20, no. 3/4, 1979, pp. 87-106.
G6ko_lu, S_leyman A.; Chen, Bor-Kuan; and Rosner, Daniel E.: Computer
Program for the Calculation of Multlcomponent Convective Diffusion
Deposition Rates from Chemically Frozen Boundary Layer Theory. NASA
CR-168329, 1984.
G6ko_lu, SUleyman Aklf: Thermophoretlcally Enhanced Deposition of
Particulate Matter Across Nonlsothermal Boundary Layers, Ph.D. Thesis,
Yale University, 1983.
Fernandez de la Mora, J.; and Rosner, D. E.: Inertial Deposition of
Particles Revisited and Extended: Eulerlan Approach to a Traditionally
Lagranglan Problem. PCH, PhyslcoChem. Hydrodyn., vol. 2, no. l, 1981,
pp. 1-21.
G6ko_lu, S. A.; and Rosner, D. E.: Correlation of Thermophoretlcally
Modified Small Particle Diffuslonal Deposition Rates in Forced Convection
Systems with Variable Properties, Transpiration Cooling and/or Viscous
Dissipation. Int. J. Heat Mass Transfer, vol. 2?, no. 5, May 1984, pp.
639-646.
Israel, R.; and Rosner, D. E.: Use of a Generalized Stokes Number to
Determine the Aerodynamic Capture Efficiency of Non-Stokeslan Particles
from a Compressible Gas Flow. Aerosol Sci. and Tech., vol. 2, no. l,
1983, pp. 45-51.
Rosner, D. E.; G6ko_lu, S. A.; and Israel, R.: Rational Engineering
Correlations of Diffuslonal and Inertial Particle Deposition Behavior in
Non-lsothermal Forced Convection Environments. Fouling of Heat Exchanger
Surfaces, Richard W. Bryers, ed., Engineering Foundation Inc., 1983, pp.
235-256.
Santoro, Gilbert J., et al.: Experimental and Theoretical Deposition
Rates from Salt-Seeded Combustion Gases of a Mach 0.3 Burner Rig. NASA
_P-2225, 1984.
Rosner, D. E.; Gunes, D.; and Nazih-Anous, N.: Aerodynamically Driven
Condensate Layer Thickness Distributions on Isothermal Cylindrical
Surfaces. Chem. Eng. Commun., vol. 24, 1983, pp. 2?5-28?.
Santoro, G. J.; G6ko_lu, S. A.; Kohl, F. J.; Stearns, C. A.; and Rosner,
D.E.: Deposition of Na2SO 4 From Salt-Seeded Combustion Gases of a
High Velocity Burner Rig. NASA TM-83751, 1984.
Sparrow, E. M.; Stahl, T. J.; and Traub, P.:
the Attached End of a Cylinder in Crossflow.
vol. 27, no. 2, Feb. 1984, pp. 233-242.
Heat Transfer Adjacent to
Int. J. Heat Mass Transfer,
112
ORIGINAL PAGE IS 
OF POOR QUALITY BURNER RIG 
COLLECTOR ASSEMBLY 
CS-83-2823 
F i g u r e  1 
BURNER RIG 
SHORT EXIT NOZZLE 
c s -83- 2822 
F igu re  2 
113 
BURNERRIGANDCOLLECTORCONFIGURATION
BURNER HOUSING
_\\\\\\\\\\\\\\\\\\\\'_
COMBUSTION PROD U_
/ IL .... PROBE I j_'//
I..//////j_/////// ,._,// / /////"L
InAIR' I_FUEL/'1_ / l
// I
_- SALT SOLUTION L To, Po
/
/- ATOMIZING
AIR
r////_
L T_, p,_, U_,
CS-B3-2812
\_--- COLLECTOR
(Tw)
Figure 3
Trap:
30--
NaCISEEDED
MELTINGPOINTOFNa2SO4 (884°C)
Na2SO4
DEPOSITION
RATE,
mg/hr
2O
10
0
500
m
/-- VAPORDEPOSITIONTHEORY(CFBL)
.._1__ O O O
- I oo_,gool
600 700 800 900 1000
COLLECTORTEMPERATURE,°C
CS-83-2816
Figure 4
114
Na2SO4
DEPOSITION
RATE,
mglhr
40 --
20--
10-
400
Na2SO4 SEEDED
Tmp: MELTING POINTOFNa2SO4 (884 %)
o o 88 °°Do0 00 0
0
I
500
VAPORDEPOSITION THEORY (CFBL)
\
I I ITmp",_0
600 700 800 900 1000
COL_CTOR TEMPERATURE,°C
CS-83-2811
I
llO0
Figure 5
FRACTION
CAPTURED
PREDICTEDDEPENDENCEOFDEPOSITIONRATEONPARTICLESIZE
i0-2
i0-4
10-6
10-3
|00__
Na2SOa DEPOSITION
P" 12 atm
Te • 1423K
CONVECTIVEDIFFUSION
_.,._ AND THERMOPHORESIS_ TwITe
-- 0.8 _ --'_
-- CONVECTIVE i/_.. - 0.8
I ,I,1,1 I , I ,I,1_ _4...J I ,I,1,1
1o-2 1o-1 1oo lo 1
PARTICLEDIAMETER,pm
C5-04-2262
Figure 6
115
Na2SO4
DEPOSITION
RATE,
mg/hr
Na2SO4 SEEDED
Trap: NELTING POINT OF Na2SO4 (884 °CI
40
F _INERTIAL IMPACTtON
,/
20 i
10--
0
40O
I
50O
vVAPOR DEPOSITION THEORY (CFBL)
I I ITm"",_° I
600 70O 80O 900 1000 1100
COLLECTORTEMPERATURE, °C
CS-83-2814
Figure 7
INITIAL DROPLETSIZE INFORMATION
COMBINEDSMD DATAVS ATOMIZINGAIR PRESSURE
SAU_R
MEAN
DIAMETER.
pm
m
20
0
I I I
t0 20
ATOMIZING AIR PRESSURE, psig
Figure 8
116
L_
DISTRIBUTION,
percent
6O
4O
2O
INITIAL DROPLETSIZEINFORMATION
TYPICALHISTOGRAM
A--
20
DROPLETDIAMETER.pm
.... I.,, D
:1 .---I-i
4O 6O
PERCENTBY NUMBER
PERCENTBYWEIGHT
SMD- 39.0 pm
Na2SO4 SOLUTION
I
8O
Figure 9
NaCI PARTICLESCAPTURED ELEMENTSDETECTEDBY EDS
0'COUNTS NaCI SEEDEDPt TARGETF/A • 0.0444
CJ ENERGY. key
4 5
CS-84-3927
Figure I0
117
Na,_SO,_PARTICLESCAPTURED ELEMENTSDETECTEDBY EDS
800--
700
COUNTS
_O0
500
Figure II
NazSO4 SEEDED
Pt TARGET
FIA - 0.0472
L 2 3 4
CS-84-3926
PARTICLE CAPTURE EXPERIMENTS
CHEMICAL ANALYSIS OF DEPOSIT
FLAMESEEDEDWITHNaCI SOLUTION
PARTICLECAPTUREDURATION.-5 sec
83% NaCl
(BY WEIGHT)
17=/, Na2SO4
OR
93% NaCI
(BY MOLE)
7_, Na2SO4
Figure 12
118
APPROACHES TO ELIMINATE PARTICLES
IA) USE Na DISPERSIONS IN UGHI OIL (OR MINERAL SPIRIT)
WHICH IS SOLUBIF IN JET A-] FUEL Na PARTICLES ARE
IN 1 TO 10 pm SIZE RANGE
(B) USE ALCOHOL AS FUEL DISSOLVE Na-ACETAIE (Na-SOURCE)
AND THIOUREA (S-SOURCE) IN ALCOHOL
iC) FUEL NOZZLE DROPLET SIZE MEASUREMENT RESULTS
ENCOURAGING
Figure 13
DETERMINATIONOF AVERAGEMASSTRANSFER
COEFFICIENT( _ Num)
"CYUNDER IN CROSSFLOW" ?
._ '"_ COLLECTOR
(3/4" 00)
i
LNOZZLE 11" OD)
Figure 14
119
TEMPERATUREDISTRIBUTIONON STATIONARYPt-Rh COLLECTOR
1300--
COLLECTOR
"II_MPERATURE,
oc
1200
1100
1000
900
= ,
I I I I I
80 120 160 200
ANGLE,deg
Figure 15
DETERMINATION OF AVERAGE MASS TRANSFER COEFFICIENT
(-----,.Num)
IA) NAPHTHALENE SUBUMAIION EXPERIMENTSFOR PRESENT
CYLINDRICALCOLLECTORS
(B) DESIGN SEGMENTED COLLECTORSTO STUDY STAGNATION
POINTMASS TRANSFER,SIMULATINGNOSEREGIONOF
BLADES
\" ,// 40o ',
Figure 16
120
SUMMARY
• CAREFULANALYSISAND INTERPRETATIONOF PREVIOUS
EXPERIMENTALRESULTS
• DETERMINATIONOF PROBLEMS
IA)
(B)
REMEDIES
(A)
(B)
(C)
PRESENCEOF PARTICLES
"CYUNDER IN CROSSFLOW"ASSUMPTIONNOT TRUE
CONTAMINATEFUEL
NAPHTHALENESUBLIMATIONEXPERIMENTS
SEGMENTEDCOLLECTORS
Figure 17
121


Experimental verification of vapor deposition model in Mach 0.3 burner rigs

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