Viscosity modifiers and gelling agents were evaluated in combination with ethylene glycol and dimethyl sulfoxide water eutectics. Pectin and agarose are found to gel these eutectics effectively in low concentration, but the anti-freeze protection afforded by these compositions is found to be marginal in simulations of the intended applications. Oxygen vent shutters and vertical metallic surfaces were simulated, with water supplied as a spray, dropwise, and by condensation from the air

Lynn, R. O. L.

English

NASA Technical Reports Server

  
 
 
N O T I C E 
 
THIS DOCUMENT HAS BEEN REPRODUCED FROM 
MICROFICHE. ALTHOUGH IT IS RECOGNIZED THAT 
CERTAIN PORTIONS ARE ILLEGIBLE, IT IS BEING RELEASED 
IN THE INTEREST OF MAKING AVAILABLE AS MUCH 
INFORMATION AS POSSIBLE 
https://ntrs.nasa.gov/search.jsp?R=19810021630 2020-03-21T12:35:52+00:00Z
April 1981
NASA TECHNICAL
MEMORANDUM
NASA TM -82431
EVALUATI ON OF ANTI -FREEZE V I SCOS I TY MOD I F I ER
FOR POTENTIAL EXTERNAL TANK APPLICATIONS
By Robert O. L. Lynn
Materials and Processes Laboratory
'6l
i^
NASA
George C. Marshall Space Flight Center
Marshall Space Flight Center, Alabama
(NASA-TM - 82431) EVALUATION OF ANTI-FREEZE
	 681-30169
VISCOSITY HODIFIB &
 FCR POTENTIAL BYTERVAL
TANK APPLIC 'ITIONS ( NASA) 15 P 8C A02/AF A01
CSCL 228	 Unclas
G3/16 27253
WIPC • Form 3100 (Row Juw 1071)
I . REPORT NO. 2, GOVERNMENT ACCESSION NO. S. RECIPIENT'S CATALOG NO.
NASA TM-82431
4. TITLE AND SUBTITLE S. REPORT DATE
Evaluatiorl of Anti -Freeze Viscosity Modifier for Potential April 1981
External Tank Applications 6. PERFORMING ORGANIZATION CODE
7, AUTHOR(S) & PERFORMING ORGANIZATION REPORT tl
Robert O. L. Lynn
g, PERFORMING ORGANIZATION NAME AND ADDRESS t0. WORK UNIT NO.
Geoi' ge C. Marshall Space Flight Center 11. CONTRACT OR GRANT NO.
Marshall Space Flight Center, Alabama
	 35812
13. TYPE OF REPORT & PERIOD COVERED
12. SPONSORING AGENCY NAMF AND ADDRESS
National Aeronautics and Space Administration Technical Memorandum
Washington, D.C.
	 20546 14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
Prepared by Materials and Processes Laboratory, Science and Engineering
16. ABSTRACT
Viscosity modifiers and gelling agents have been evaluated in combination
with ethylene glyc-)l and dimethyl sulfoxide water eutectics. Pectin and agarose
were found to gel these eutectics effectively in low concentration, but the anti-freeze
protection afforded by these compositions was found to be marginal in simulations of
the intended applications. Oxygen vent shutters and vertical metallic surfaces were
simulated, with water supplied as a spray, dropwise, and by condensation from the
air.
3
1	 ^
a
i
17. KEY WORDS
Ice Prevention
Space Shuttle External Tank
Gelling Agents
Dimc.thyl Sulfoxide
Ethylene Glycol
Pectin
18. SECURITY CLASSIF. (of thle teyattl	 20. SECURITY CLASSIF. (et thle pe6e)	 21. N0. OF PAGES 22, PRICE
Unclassified	 Unclassified	 13	 NTIS
MBFC • Form 3292  (Rev. December 1.7 S)	 For eale by National Technical Information Service, Sptlutfla !d, V 1,41nla 33 161
16. DISTRIBUTION STATEMENT
Unclassified — Unlimited
iACKNOWLEDGMENTS
i
The assistance of Mr. J. T. Schell and the Polymers and Composites
Branch in fabricating and setting up much of the experimentai hardware
is gratefully acknowledged. Mr. R. L. Durham of that Branch was par-
ticularly helpful.
Samples of pectin were provided by Mr. Terry Schneider of Rock-
well International, Downey, California, who was also most helpful in
giving background information concerning experimentation performed at
his location.
3
n
I[,- ' -
i
r
TABLE OF CONTENTS
z
Page
INTRODUCTION	 ............................................... 1
EXPERIMENTAL	 ................................................ 1
DISCUSSION ................................................... 4
CONCLUSIONS	 ................................................. 5
BIBLIOGRAPHY	 ................................................ 10
LIST OF ILLUSTRATIONS
Figure	 Title	 Page
1. ET GO 2 vent /relief valve and manifold ................
	
8
2. ET relief louver simulation ............................
	 9
LIST OF TABLES
	
Table	 Title	 Page
1. Selected Physical Properties Comparison ...............
	 6
2. Solution Properties .................................... 	 7
TECHNICAL MEMORANDUM
EVALUATION OF ANTI-FREEZE VI SCOS ITY MODIFIER
FOR POTENTIAL EXTERNAL TANK APPLICATIONS
INTRODUCTION
The Space Shuttle External Tank (ET) has several areas which are
•	 subjet.K :o ice /frost formation. These consist of protrusions which are
not coverer' b. thermal protection, and louvers in the oxygen vent sys-
tem (Fig.
	
While frost formation is relatively harmless, thick accumu-
lations of ire on the Shuttle side of the ET can present hazards to the
Shuttle's thermally protective tiles.
Various proposals have been made to prevent or eliminate such ice
formations, including the r ise of tot gases or antifreeze liquids. The
hot gas concept requires large capital outlays and presents the potential
hazards associated with the use of large volumes of uncontained oxygen-
poor atmospheres. The anti-freeze liquids tend to be highly fugitive,
draining away rapidly. To counter this latter drawback, Rockwell
i	 International proposed the use of a gelling agent, specifically the pectin/
dimethyl sulfoxide (DMSO) combination. i
This present work has undertaken to evaluate this proposal and the
overall general concept. It was decided to limit the anti-freeze liquids to
DMSO, as chosen by Rockwell, and the commonly used ethylene glycol.
A list of thickening/ gelling agents was drawn up, but not all were
i	 evaluated, for reasons of availability, relative complexity, etc.
EXPERIMENTAL
iDe-Icers	 ±
1) Dimethyl sulfoxide
2) Ethylene glycol.
Viscosity Modifiers
1) Acrylamide	 5) Hydroxy methyl cellulose
2) Agarose	 6) Pectin
.i 3) Gelatin	 7) Sodium alginate
4) Gum tragacanth	 8) Starch.	 ii
Solution Preparation
Generally, solutions were prepared in 50 ml quantities, using a
magnetic stirrer and heating to 1020 to 16100. The Makener was die-
persed in the de-icer prior to addition of the water and application of
heat. Solutions were allowed to cool without agitation, In the prepara-
tion of "micro-gels," solutions were prepared as above in 100 ml quanti-
ties, followed by cooling with v gorou:s stirring. Agitation was provided
by a split-disc type propeller, using speeds sufficient to maintain a
vortex.
Solution Properties
1) Acrylemide was not tested since gel-formers were found which
were simpler than this precise three component system.
2) Gelatin appeared to have limited solubility and formed only
gelatinous inhomogeneities.
3) Gum tragacanth increased the viscosity of the eutectics and
oauld be useful at higher concentrations. Insoluble components were
noted in accordance with literature notations.
4) Sodium alginate and hydroxy methyl cellulose were not evaluated
for reasons of timing and availability.
5) Starch was not effective at the 2 percent level.
6) Agarose powder (Bic-Rad Laboratories, Richmond, California)
was found to be an excellent E;el-former. Gels may be destroyed by
heating and do not re-form upon subsequent cooling. "Micro-gels"
having a paste-like consistency may be formed by cooling with vigorous
agitation. An endotherm was noted in the 12 0 to 14°C range while
cooling with ice to form these microgels. These gels and microgels do
not dissolve readily in water and do not tend to completely dry out upon
exposure to the room atmosphere for several days. Gel firmness is
dependent upun agarose concentration.
7) Citrus pectin (Atlantic Gelatin, General Foods Corporation,
Hollywood, California) produced gels as reported by Rockwell International.
Powder solubilities appeared to be somewhat lower than those with agarose,
but the gels were more water-soluble. Gel-forming minimum concentrations
were greater than with agarose, and gel formation occurred over a broad
`	 temperature band during the cooling process. Micro-gels could not be
formed with the agitation employed, but rather, large gel particles were
produced.
2
Evaluation of Ae; Anti-Freese Properties
Evaluations were conducted on the vertical sides of a steel beaker,
copper piping, and a louver simulation.
1) The louver simulation consisted of 11/16 in. wide alumirwa
strips embedded at 450 angles in one end of a 2 in. I.D. cork cylinder,
with 1/4 in. spacing between strips. This construction was attached to
a 3 in. pipe from a liquid nitrogen storage vessel. Gaseous nitrogen
was periodically vented through these louvers at high flow rates. Figure
2 shows this set-up, without the gels applied.
Gels applied to the se metal "louvers" adhered reasonably well
to the upper surface, but were blown off the underside. Micro-gels
could be applied more easily and evenly, bi., were also blown off the
bottom surface. Ethylene glycol gels tended to be harder and flake off
more readily than did DMSO gels. When stored inside, the gels lasted
for about a week before the liquid components evaporated. Rain washed
away the gels.
No frost formation was noted on gel coated surfaces under con-
ditions of the tests.
2) For simulation of uninsulated tank hardware, the vertical sides
of a two-liter steel beaker were used. Liquid nitrogen was passed
through cooling coils submerged in ethanol to cool the beaker. Tempera-
ture measurements were made with a thermocouple immersed in the circu-
lating ethanol. Temperatures as low as -93 10C wcxe obtained. Gels were
applied to the side of the beaker with a spatula. Water was supplied
either as moisture condensation from the air, in the form of a fine spray
from a gun, or in a stream from a squeeze bottle. Considerable difficulty
was experienced in getting normal gels to cling to the beaker sides, and
an even coating was impossible. Dispersion of the gels in gum tragacanth
solution improved the adherence but the gel lumps still caused uneven
coating. Microgel pastes could be applied smoothly and evenly and
adhered well.
For the controlled thickness experiments, cardboard was taped
to the beaker sides to form a well, which was filled with the microgels.
In all cases, gels were applied at room temperature and then cooling was
begun.
Thin Coatings (ca. 50 mils)
a) DMSO (60/40) with pectin frosted over by the time the bath
	 i►
was cooled to -620C and water rivulets froze on the surface when applied
0at -82 C. A 50:50 mixture of this material and the DMso 70/30 agarose 	 i
microgel gave the same results. The pectin microgel does not adhere
significantly better than the normal gel. 	 I
3
Tom-
b) DMSO (70/30) apron miarr44 hosted over very slightly but
slower than the combinations above. When sprayed with a water mist at
-400C.
 a hard im coating formed over the pliable gsl substrate.
c) Ethylene glycol (75/85) agarose microgel results were similar
to those in b) , with a slightly stiffer gel substrate.
Thicker Coatings
Ethylene glycol (75/85) agarose microgel:
a) 100 mils frosted at -51°C
b) 200 mils frosted at -93°C
c) 300 mils no frost at -93°C .
All ooatings shrink drastically at -930C, recover at room tempera-
ture but tend to "mud-crack" upon recovery. Some liquid loss probably
occurred during the overnight warming process.
3) In an attempt to evaluate temperatures closer to -185 0C, gels
were applied to copper piping leading from the LN 2 dewar. Temperature
was measured by means of a thermocouple at the pipe surface below the
go'.. Temperatures as low as -166°C w:xe attained.
a) The ethylene glycol ( 75/25) agarose microgel in 400 mil
thickness formed a light frost at -140 0C, and a heavy frost at -1660C.
A drop of water placed on this surface froze immediately but the gel
was pliable underneath down to the pipe surface.
b) DMSO (60/40) pectin gel in 600 mil thickness formed heavy
frost at -148°C and also froze a drop of water placed on the surface.
The gel remained flexible.
Both the glycol microgel and DMSO gel formed brittle solids when plunged
into liquid nits-ogen. When warmed to room temperature, no differences
were detected compared to the original gels.
DISCUSSION
While the Rockwell International work was done using a 50 percent
(volume) solution of DMSO in water, much of this work was done at the
higher end of the eutectic range. This was done based upon the premise
that water contacting the surface will dilute the interface. In test con-
figurations, no differences in effectiveness were detected.
i
4
DMSO appears to be relatively more flammable than ethyl one glycol,
And the gale also appear to burn more readily. Both gels extinguish
when the flame is removed and, indeed, drips from the glycol tended to
extinguish the applied flame. Although the vapor pressure of DMSO is
relatively low at room temperature, exposed gels give rise to somewhat
noxious odors.
Caution must be used in working with DMSO due to its well known
solvating power and ability to permeate human skin. Thus, while not
particularly toxic itself, it could solvate some available toxins and facilitate
•	 their entry into the human body.
CONCLUSIONS
1) Microgels, having a paste-like consistency, can be more effec-
tively applied to vertical surfaces than can conventional gels. These
could be formed readily with agarose, but not with pectin.
2) Ethylene glycol is preferred . j DMSO for reasons of reduced
flammability, health hazard potential, lower evaporation rate, and broader
eutectic range.
3) Gelled antifreeze is effective for substrate surface temperatures
in the -18°C range, but ineffective for -184°C substrate temperatures
when used in "reasonable" thicknesses. It is highly probable that the
insulating properties of the gels contribute more to their effectiveness
than does the V)rmation of an eutectic with added water.
4) Pectin gels are readily dissolved by liquid water, unlike
agarose gels. In theory, pectin should be more effective in the preven-
tion of ice or ice /frost formation. In practice, at cryogenic substrate
temperatures, the gel surface itself is cold enough to form ice before any
solvation can occur.
5
TABLE I. SELECTED PHYSICAL PROPERTIES
COMPARISON
Ethylene Glycol Dimethyl Sulfoxide
Molecular Weight 62.07 78.13
BoilinT Point 197.6 159.0
( 760 mm Hg, DO
Vapor Pressure 0.06 0.417
(20°C, mm Hg)
Frae zin g Point (°C) -13 18
Density (20°C, g/cc) 1.11 1.10
Viscosity (20 0C, cp) 20.9 2.47
Surface Tension 48.4 46.2
(200C, dynes /cm )
Coefficient of Expansion 6.2 x 10- 4 8.8 x 10 - 4
(20°C, cm3 /10C)
Flash Point 95°C
Spontaneous ignition 480°C 301°C
Temperature in Air
Heat of Combustion -283.3 kcal /mol -472.9 kcal /mol
020°C 825''C
Range of Eutectic (wt . %) 58-80 55-70
6
NI.a
CC1
Q
H
aM t, 0
C r
^ t ^
^
a
A
u a s
ater
in
4+ O
U V N
^. N
o
E E
4 .Nr
O
O
w $ s .. .. :.
c
c
s
c
o,
«.c^
, 0
.:
U be
r
U v, •• •. ••
4;;.4
E
a
.,d
.g
c
E N
f
41 r a g'z r. 0
u ^' ,; tc.
3
E Eu
^' rr a c. m 0.
tcy.
O.
^
g
'O
C
of
w
O 7 Op
>` u u u u E E E 6t 5C 6c
E
E
E U) °(Q c c N V N U ^^ U U 4d ►. ^/ cO. ••~c y
ci E E E
t 0 o L c
a
c
G o
°•ao co o'no w ¢ _ Ot.
O > > > > > O O O O L t t
V ^ .yt. 4J ^ d G ^ a:
,. « « .. d ..
g
..
g
Q^ U >'
.• U .• «• E E a
^
s
cr
a c
.^ E
a
O
c ',.'. v^ :Z .: N ^ L V C: ^ ^
^E
c 0:.
a
to
N N
ybeN N
N
..
N
..
V N N O
E N N ` N .-. N N ', d N ... .r
u °o
z c ^. «. F, F.
Q
IF
c c c
.r
c c
c c E E c
be bt v u u u cb. be u u `^ Do
H E c~n V V :: < 4 C^ a^'. a Gu. < C c°i. c eL
cL
v
C
.'r O p O O O O O O O O O O O N O O N N
i. Q e !— e e M_ O N fi N a^ M N NW
.7 V
O
t0
O
t0
O
t0
O
CO
O
w
O
w
O
tD
O
t0
O
CO
O
t^
R O
N
s O &M O O
tr
^If
t-
41
^
0 0 8 0 0 0 0 oLr 0 GU 8 p8
>' > i > r S i t i. >' S > 5 >'d
G G J G :: G .. ^. :; G G G G L G J G G :: ::
my.rH
a
a
a
zO
a
cc
C
t4
rd
• o
.0
I
VL-^
R-
k
w
vo
^. c
^cI
^M
L7 ,
N
x cl;
g^
r. -
u Lol
A A
^^ O
Cl
E H
u^
•c
o, r.
a ^
a H
U
E
q
CJ
d
W
tip.IGINAI. P AGE IS
OF POOR QUA ""N'
8
1 ,,yAr'
I^
I=
i
N i
"l-ICINAL PAGE: IS
OF PQr ►R QI UA LITY
I
BIBLIOGRAPHY
Martin, Dieter and Hauthal, Herman G.: Dimethyl Sulphoxide. John
Wiley and Sons, New York, 1975.
Curme, George O. , Jr. and Johnston, Franklin, Editors: Glycols.
Reinhold Publishing Corporation, New York, 1952.
Rasmussen, D. H. and MacKenzie, A. P.: Phase Diagram for the System
Water-Dimethyl Sulphoxide. Nature. Vol. 220, pp. 1315-17, 1968.
1	
10
APPROVAL
EVALUATION OF ANTI-FREE7_E VISCOSITY MODIFIERS
FOR POTENTIAL EXTERNAL TANK APPLICATION'S
&'	 BY ROBERT O. L. LYNN
The information in this report has been reviewed for technical content
Review of an y information concerning Department of Defense or nuclear
energy activities or programs has been made b y the MSFC Security Classi
fication Offices. This re port, in its entiretN• , has been determined to be
unclassified.
JOHN R. NUNNELT.EY
Chief, Anal ytical and Ph ysical Chemistr y Branch
L < 'n C
.i	 L L
AMES E. CURRY"
Chief, Non-Metallic Materials Division
ROBERT, J. SCHt INFMNT JR
Director
Materials and Processes Laboratory


Evaluation of anti-freeze viscosity modifier for potential external tank applications

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server