Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
35~
A METHOD FOR CONTROLLING TH~ OVERALL HEAT
TRANSFER COEFFICIENT OF A HEAT E~CHANGE FLUID
The present invention relates to a method for
controlling the heat transfer coefficient of a heat
exchange fluid for use in transfer applications.
In many heating and cooling applications heat
is transferred between a heating source and a heat sink
by continuously circulating a fluid around a closed
loop between the source and -the sink. It is desirable
to reduce the amount of pipe flow fraction (i.e., drag)
of the fluid being recirculated and thus reduce the
amount of pumping energy employed during the transfer
of the fluid between the source and the sink, expand
capacity for an existing system, or lower capi-tal costs
for construction of a new system.
Heretobefore, various alternatives have been
proposed in an attempt to expand the capacity of an
existing heat transfer system or to reduce the amount
of energy employed in continuously circulating fluids
in heat transfer applications. It is disclosed that
polymeric materials can be added to fluids in order to
--2--
~35~4
reduce the amount of circulation energy. See, for
example, C~o and Hartnett, Advances ln Heat Transfer,
15, pg. 59 (1981). Unfor-tunately, such polymeric drag
reduction additives significantly reduce the heat
transfer coefficient of the aqueous fluids which are
employed. In addition, polymeric drag reduction addi-
tives are mechanically degraded due to the shearing
action of pumps, and the like.
This invention is directed to a me-thod for
controlling the overall heat transfer coefficient of a
heat exchange fluid characterized (A) by incorporating
in the heat exchange fluid a functionally effective
amount of a viscoelastic surfactant composition which
comprises (1) a surfactant compound having a hydrophobic
moiety chemically bonded to an ionic, hydrophilic
moiety and (2) an electrolyte having a moiety that is
capable of associating with the surfactant ion to form
a viscoelastic surfactant and (B) by providing a flow
rate and a temperature of the heat exchange fluid such
that the heat transfer fluid has the desired overall
heat transfer coefficient. Optionally, a further
amount of an electrolyte having a moiety that is capable
of associating with the surfactant ion is incorporated
in the viscoelastic surfactant composition. For
purposes of this invention, a viscoelastic surfactant
is a compound having ~1) an ion capable of acting as a
surfactant and (2) a stoichiometric amount of a
counterion that associates with the surfactant ion to
render it viscoelastic as defined hereinafter. The
further amount of electrolyte can be -the same or
different from that counterion associated with the
surfactant ion. The resulting viscoelastic surfactant
is employed in an amount sufficient to reduce the amount
5~
--3--
of friction experienced by the heat transfer fluid in
the hea-t -transfer apparatus. The fluids employed in
this invention are highly shear s-table and do not
experience any loss of friction reduction activi-ty with
continued pumping, as compared to polymeric drag
reduction additives which undergo irreversible mechanical
degradation and rapid loss of friction reduction activity
with continued pumping.
Surprisingly, the presence of the additional
electrolyte in an aqueous liquid containing the visco-
elastic surfactant in accordance with the practice of
this invention significantly further reduces the fric-
tion both over velocities and temperatures experienced
by the fluid containing the viscoelastic surfactant as
the liquid is employed in heat transfer applications.
The admixture of the aqueous liquid, electrolyte and
viscoelastic surfactant is significantly more shear
stable than an aqueous liquid containing a polymer
capable of providing the aqueous liquid with the same
degree of friction reduction.
In another aspect, the present invention is a
method for imparting shear stable heat transfer proper~
ties to fluids through the use of a nonionic visco-
elastic surfactant. This method comprises contacting
said aqueous liquid with a functionally effective
amount of a surfactant compound having a hydrophobic
moiety chemically bonded to a nonionic, hydrophilic
moiety (hereinafter a nonionic surfactant), which
compound is capable of exhibiting a viscoelastic char-
acter. The nonionic viscoelastic surfactant is employedin an amount sufficient to reduce the amount of friction
experienced by the heat transfer fluid as it is employed
in the heat transfer apparatus.
3524
--4--
The method of this invention is useful in
those processes where fluids are employed in general
lubricating and heat transfer applications such as
various closed-loop recirculating systems. O~
particular interest are district heating applica-tions
and hydronic heating, cooling applications, and the
like.
As used herein, the term "fluid" refers to
those fluid materials which can be employed in heat
transfer applications. Heat transfer 1uids can be
organic or aqueous in nature. Most preferably, the
fluid is an aqueous liquid. As used herein, the term
"aqueous liquid" refers to those liquids which contain
water. Included within the term are aqueous liquids
containing inorganic e1ectrolytes, such as aqueous
solutions of inorganic salts, aqueous alkaline or
aqueous acidic solutions, depending upon the particular
surfactant and electrolyte employed, e.g., an aqueous
solution of an alkali metal or alkaline earth metal
hydroxide. Other exemplary aqueous liquids include
mixtures of water and a water-miscible liquid such as
lower alkanols, e.g., methanol, ethanol or propanol;
glycols and polyglycols, provided that such water-
-miscible liquids are employed in amounts that do not
deleteriously affect the viscoelastic properties of the
aqueous liquid. Also included are emulsions of
immiscible liquids in the aqueous liquid, aqueous
slurries of solid particulates such as corrosion
inhibitors, biocides or other toxicants. In general,
however, water and aqueous alkaline, aqueous acidic or
aqueous inorganic salt solutions (i.e., brine solutions)
are most beneficially employed as the aqueous liquid
herein. Advantageously, the electrolyte concen-tration
1~352~
--5--
is less than 75, preferably less than 15, more preferably
less than 5, especially less than 1, percent by weight
of the solution. Most preferably, -the aqueous liquid
is ~ater.
The term "viscoelastic" as it applies to
liquids, means a viscous liquid having elastic proper-
ties, i.e., the liquid at least partially returns to
its original form when an applied stress is released.
The property of viscoelasticity is well-known in the
art and reference is made to H. A. Barnes et al.,
Rheol. Acta, 1975 14, pp. 53-60 and S. Gravsholt,
Journal _ Coll. and Interface Sci., 57 (3) pp. 575-6
(1976). These references contain a definition of
viscoelasticity and tests to determine whether a liquid
possesses viscoelastic properties. See also, N. D.
Sylvester et al., Ind. ~ Chem. Prod. Res. Dev.,
1979, 1~, p. 47. Of the test methods specified by
these references, one test which has been found to be
most useful in determining the viscoelasticity of an
aqueous solution consists of swirling the solution and
visually observing whether the bubbles created by the
swirling recoil after the swirling is stopped. Any
recoil of the bubbles indicates viscoelasticity.
Surfactant compounds within the scope of this
invention include compounds broadly classified as
surfactants which, through the proper choice of counter-
ion structure and environment, give viscoelasticity.
The term "surfactant" is taken to mean any molecule
having a characteristic amphiphatic structure such that
it has the property of forming colloidal clus-ters,
commonly called micelles, in solution.
5;~
--6--
In general, ionic surfactant compounds comprise
an ionic hydrophobic molecule having an ionic, hydro-
philic moiety chemically bonded to a hydrophobic moiety
(herein called a surfactant ion) and a counterion
sufficient to satisfy the charge of the surfactant ion.
Examples of such surfactant compounds are represented
by the formula:
Rl(Y~)X or Rl( ze )A~
wherein R1(Y~) and Rl(Ze) represent surfactant ions
having a hydrophobic moiety represented by R1 and an
ionic, solubilizing moiety represented by the cationic
moiety (Y~) or the anionic moiety (Ze) chemically
bonded thereto. X~ and A~ are the counterions associ-
ated with the surf~ctant ions.
In general, the hydrophobic moiety (i.e., Rl)
of the surfactant ion is hydrocarbyl or inertly substi-
tuted hydrocarbyl wherein the term "inertly substituted"
refers to hydrocarbyl radicals havlng one or more
substituent groups, e.g., halo groups such as -F, -Cl
or -Br or chain linkages, such as a silicon linkage
(-Si-), which are inert to the aqueous li~uid and
components contained therein. T~pically, the hydro-
carbyl radical is an aralkyl group or a long chain
alkyl or inertly substituted alkyl, which alkyl groups
are generally linear and have at least 12, advantageously
at least 16, carbon atoms. Representative long chain
alkyl and alkenyl groups include dodecyl (lauryl),
tetradecyl ~myristyl), hexadecyl (cetyl), octadecenyl
(oleyl), octadecyl (stearyl) and the derivatives of
tallow, coco and soya. Preferred alkyl and alkenyl
i35;~
--7--
groups are generally alkyl and alkenyl groups having
from 14 to 24 carbon atoms, with octadecyl, hexadecyl,
erucyl and tetradecyl being the most preferred.
The cationic, hydrophilic moieties (groups),
i.e., (Y~), are generally onlum ions wherei~ the term
"onium ions" refers to a cationic group which is essen-
tially completely ionized in water over a wide range of
p~, e.g., pH values from 2 to 12. Representative onium
ions include quaternary ammonium groups, i.e., -N~(R)3;
tertiary sulfonium groups, i.e., -S~(R)2; and quaternary
phosphonium groups, i.e., -P~(R)3, wherein each R is
individually a hydrocarbyl or inertly substituted
hydrocarbyl. In addition, primary, secondary and
tertiary amines, i.e., -NH2, -NHR or -N(R)2, can also
be employed as the ionic moiety if the pH o~ the aqueous
liquid being used is such that the amine moieties will
exist in ionic form. A pyridinium moiety can also be
employed. Of such cationic groups, the surfactant ion
of the viscoelastic surfactant is preferably prepared
having guaternary ammonium, i.e., -N~(R)3; a pyridinium
moiety; an aryl- or alkaryl pyridinium; or imadazolinium
moiety; or tertiary amine, -N(R)2, groups wherein each
R is independently an alkyl group or hydroxyalkyl group
having from 1 to 4 carbon atom~, with each R preferably
being methyl, ethyl or hydroxyethyl.
Representative anionic, solubilizing moieties
(groups) (Ze) include sulfate groups, i.e., -OS03e
ether sulfate groups, sulfonate groups, i.e., -S03 ,
carboxylate groups, phosphate groups, phosphonate
groups, and phosphonite groups. Of such anionic groups,
the surfactant ion of the viscoelastic surfactants is
preferably prepared having a carboxylate or sulfate
~ bi3S~
--8--
group. For purposes of this invention, such anionic
solubilizing moie-ties are less preferred than cationic
moieties.
Fluoroaliphatic species suitably employed in
the practice of this invention include organic compounds
represented by the formula:
RfZl
wherein Rf is a saturated or unsaturated fluoroaliphatic
moiety, preferably containing a F3C- moiety and Zl is
an ionic moiety or potentially ionic moiety. The
fluoroaliphatics can be perfluorocarbons. Suitable
anionic and cationic moieties will be described
hereinafter. The fluoroaliphatic moiety advantageously
contains from 3 to 20 carbons wherein all can be fully
fluorinated, preferably from 3 to 10 of such carbons.
This fluoroaliphatic moiety can be linear, branched or
cyclic, preferably linear, and can contain an occasional
carbon-bonded hydrogen or halogen other than fluorine,
and can contain an oxygen atom or a trivalent nitrogen
atom bonded only to carbon atoms in the skeletal chain.
More preferable are those linear perfluoroaliphatic
moieties represent~d by the formula: CnF2n+l wherein n
is in the range of 3 to 10. Most preferred are those
linear perfluoroaliphatic moieties represented in the
paragraphs below.
The fluoroaliphatic species can be a cationic
perfluorocarbon and is preferably selected from a member
of the group consisting of CF3(CF2)rSO2N~(CH2)SN R'3~ ;
RFCH2CH2SCH2CH2N~R 3X and CF3(CF2)rCONH(CH2)sN R"3X ;
wherein Xe is a counterion described hereinafter, R" is
1~352~
g
lower alkyl containing between 1 and ~ carbon atoms, r
is 2 to 15, preferably 2 to 6, and s is 2 to 5. Examples
of other preferred cationic perfluorocarbons, as well
as methods of preparation, are those listed in U.S~
Patent No. 3,775,126.
The fluoroaliphatic species can be an anionic
perfluorocarbon and is preferably selected from a
member of the group consisting of CF3(CF2) SO2OeA~,
CF3(CF2)pCOO A , CF3(CF~)~S02NH(CH2)~S020eA~ and
CF3(CF2)pSO2NH~CH2)qCOO A ; wherein p is from 2 to lS,
preferably 2 to 6, q is from 2 to 4, and A is a
counterion described hereinafter. Examples of other
preferred anionic perEluorocarbons, as well as methods
of preparation, are illustrated in U.S. Patent No.
3,172,910.
The counterions (i.e., X~ or A~) associated
with the surfactant ions are most suitably ionically
charged, organic materials having ionic character
opposite that of the surfactant ion, which combination
of counterion and surfactant ion imparts viscoelastic
properties to an aqueous liquid. The organic material
having an anionic character serves as the counterion
for a surfactant ion having a cationic, hydrophilic
moiety, and the organic material having a cationic
character serves as the counterion for the surfactant
ion having an anionic, hydrophilic moiety. In general,
the preferred counterions exhibiting an anionic charac-
ter contain a carboxylate, sulfonate or phenoxide group
wherein a "phenoxide group" is ArO~ and Ar represents
an aromatic ring or inertly substituted aromatic ring.
Representative of such anionic counterions which, when
employed with a cationic surfactant ion, are capable of
352~
--10--
imparting viscoelastic properties -to an aqueous liquid
include various aromatic carboxylates such as
o-hydroxybenzoate; m- or p-chlorobenzoate, methylene
bls-salicylate and 3,4-, 3,5- or 2,4-dichlorobenzoate;
aromatic sulfonates such as ~-toluene sulfonate and
naphthalene sulfonate; and phenoxides, particularly
substituted phenoxides; where such counterions are
soluble; or 4-amino-3,5,6-trichloropicolinate.
Alterna-tively, the cationic counterions can contain an
onium ion, most preferably a quate~nary ammonium group.
Representative cationic counterions containing a
guaternary ammonium group include benzyl trimethyl
ammonium or alkyl trimethyl ammonium wherein the alkyl
group is advantageously octyl, decyl, dodecyl, or
erucyl; and amines such as cyclohexyl amine. It is
highly desirable to avoid stoichiometric amounts of
surfactant and counterion when the alkyl group of the
counterion is large. The use of a cation as the counter-
ion is generally less preferred than the use of an
anion as the counterion. Inorganic counterions, whether
anionic or cationic, can also be employed.
The particular surfactant ion and the
counterion associated therewith are selected such that
the combination imparts viscoelastic properties to an
aqueous liquid. Of the aforementioned surfactant ions
and counterions, those combinations which form such
viscoelastic surfactants will vary and are easily
determined by the test methods hereinbefore described.
Of the surfactants which impart viscoelastic properties
to an agueous liquid, the preferred surfactant compounds
include those represented by the formula:
~i3~
cH3 tCH2~ N~R xe
R
wherein n is an integer from 13 to 23, preferably an
integer from 15 to 21; each R is independently hydrogen
or an alkyl group, or alkylaryl, or a hydroxyalkyl
group having from 1 to 4 carbon atoms, preferably each
R is independently methyl, hydroxyethyl, ethyl or
benzyl, and Xe is o-hydroxy benzoate, _- or
~-halobenzoate or an alkylphenate wherein the alkyl
group is advantageously from 1 to 4 carbon atoms. In
addition, each R can form a pyridinium moiety.
lS Especially preferred surfactant ions include
cetyltrimethylammonium, oleyltrimethylamrnonium,
erucyltrimethylammonium and cetylpyridinium.
Other preferred surfactant compounds include
those represented by the formula:
R
'~R e
CF3 - ( CF2 ~ n- S02NH ( CH2 ) m, x
R
wherein n is an integer from 5 to 15, preferably from 3
to 8; m is an integer from 2 to 10, preferably from 2
to 5; R is as previously defined, most preferably
methyl; and x9 is as previously defined.
~3S~4
-12-
The viscoelastic surfactants are easily
prepared by admixing the basic form of the desired
cationic surfactant ion (or acidic form of the desired
anionic surfactant ion) with a stoichiometric amount of
the acidic form of the desired cationic counterion (or
basic form of the desired anionic counterion). Alter-
natively, stoichiometric amounts of the salts of the
cationic surfactant ion and the anionic counterion (or
equimolar amounts of the anionic surfactant ion and
cationic counterion) can be admixed to form the visco-
elastic surfactant. See, for example, -the procedures
described in U.S. Patent 2,541,816.
In general, surfactant compounds having a
hydrophobic moiety chemically bonded to a nonionic,
hydrophilic moiety are those nonionic surfactants which
exhibit a viscoelastic character, and are typically
described in U.S. ~atent No. 3,373,107; and those
alkylphenyl ethoxylates as are described by Shinoda in
Solvent Properties of Surfactant Solutions, Marcel
Dekker, Inc. (1967). Preferred nonionic surfactants are
those tertiary amine oxide surfactants which exhibit
viscoelas-tic character. In general, the hydrophobic
moiety can be represented as the previously described
Rl. It is understood that the nonionic surfactant can
be employed in the process of this invention in combina-
tion with an additional amount of an electrolyte as
described hereinafter. It is also desirable to employ
an additive such as an alkanol in the aqueous liquid to
which the nonionic surfactant is added in order to
render the surfactant viscoelastic.
Other ~iscoelastic surfactants which can be
employed in the pxocess of this invention are described
s
by D. Saul et al., J. Chem. Soc, ~araday Trans., 1
(197~) 70(1), pp. 163-170.
The viscoelastic surfactant (whether ionic or
nonionic in character) is employed in an amount sufficient
to impart viscoelastic properties to the fluid, wherein
the viscoelasticity of the fluid is measured by the
techniques described herein. In general, such amount
of viscoelastic surfactant is sufficient to measurably
reduce the friction exhibited by the fluid as it is
employed in heat transfer applications. The specific
viscoelastic surfactant employed and the concentration
thereof in the fluid are dependent on a variety of
factors including solution composition, temperature,
and shear rate to which the flowing fluid will be
subjected. In general, the concentration of any specific
viscoelastic surfactant most advantageously employed
herein is easily determined by experimentation. In
general, the viscoelastic surfactants are preferably
employed in amounts ranging from 0.01 to 10 weight
percent based on the wei~ht of the surfactant and
fluid. The viscoelastic surfactant is more preferably
employed in amounts from 0.05 to 1 percent based on the
weight of the fluid and the viscoelastic surfactant.
In one highly preferred aspect of the practice
of this invention, an electrolyte having an ionic
character opposite to that of the surfactant ion and
capable of being associated as an organic counterion
with said surfactant ion is employed in an additional
amount to further reduce the friction exhibited by the
fluid containing the viscoelastic surfactant and to
increase the temperature to which the fluid will maintain
52~
-14-
drag reduction. Such electrolytes most suitably employed
herein include those containing organic ions which,
when associated with the surfactant ions of the surfactant
compound, form a viscoelas-tic surfactant. The organic
electrolyte, when present in an excess of tha-t which
stoichiometrically associates with the surfactant ion,
is capable of further reducing friction of the fluid
and to increase the temp~rature to which the fluid will
maintain drag reduction. Such organic electrolyte is
soluble in the fluid containing the viscoelastic
surfactant
The concentration of the organic electrolyte
required in the fluid to impart the further reduction
in friction and increase the temperature to which the
fluid will maintain drag reduction is dependent on a
varie-ty of factors including the particular fluid,
viscoelas-tic surfactant and organic elec-trolyte employed,
and the achieved reduction in drag. In general, the
concentration of the organic electrolyte will advanta-
geously range from 0.1 to 20, preferably from 0.5 to 5,
moles per mole of the viscoelastic surfactant.
In general, the organic ions are formed by
the dissociation of corresponding organic electrolytes,
including salts and acids or bases of a suitable organic
ion. For example, an organic electrolyte which, upon
dissociation, forms an anion will further reduce the
friction of a fluid containing a viscoelastic surfactant
having a cationic surfactant ion. Examples of such
anionic organic electrolytes include the alkali metal
salts of various aromatic carboxylates such as the
3SZ~
-15-
alkali metal aromatic carboxylates, e.g., sodium
salicylate and potassium salicylate and disodium methylene-
bis(salicylate~; alkali metal ar-halobenzoates, e.g.,
sodium ~-chlorobenzoate, potassium m-chlorobenzoate,
sodium 2,~-dichlorobenzoate and potassium 3,5-dichloro-
benzoate; aromatic sulfonic acids such as p-toluene
sulfonic acid and the alkali metal salts thereof;
napthalene sulfonic acid; substituted phenols, e.g.,
ar,ar-dichlorophenols, 2,4,5-trichlorphenol, t butyl-
phenol, t-butylhydroxyphenol, and ethylphenol.
A cationic organic electrolyte which, upon
dissociation, forms a cation is also useful in further
reducing the friction of a fluid containing a visco-
elastic surfactant having an anionic surfactant ion.
While cationic organic electrolytes are less preferred
than the aforementioned anionic organic electrolytes,
examples of suitab:le cationic electrolytes include the
quaternary ammonium salts such as alkyl t~imethyl-
ammonium halides and alkyl triethylammonium halides
wherein the alkyl group advantageously contains 4 to 22
carbons and the halide advantageously is chloride; aryl
and aralkyl trimethyl ammonium halides such as phenyl
trimethyl and benzyl trimethyl ammonium chloride; and
alkyl trimethyl phosphonium halides. Also desirable is
cyclohexyl amine. It is highly desirable to avoid
stoichiometric amounts of surfactant and counterion
when the alkyl group of the counterion is large
~i.e., greater than 8).
Preferably, the organic electrolyte is the
same or gPnera-tes the same ion associated with the
surfactant ion of the viscoelastic surfactant contained
by the aqueous liquid, e.g., alkali metal salicylate is
12~i3~Z'~
-16-
advantageously employed as the additional organic
electrolyte when the viscoelastic surfactant is origi-
nally prepared having a salicylate or p-toluene sulfon-
ate counterion. Therefore, the most preferred organic
electrolytes are the alkali metal salts of an aromatic
carboxylate, for example, sodium salicylate or sodium
p-toluene sulfonate. Moreover, it is also understood
that the electrolyte can be different from the counter-
ion which is employed.
It is also possible to employ a water-insoluble
active ingredient such as an oil or other organic
ingredient emulsified in water at a concentration of
0.05 to 80 percent. Viscoelastic surfactants (whether
ionic or nonionic in character) employed in such
emulsions tend to lose their viscoelasticity. This is
believed to be due to the fact that the oil penetrates
the micelles and destroys the aggregates required for
viscoelasticity. Viscoelastic surfactants containing
excess organic electrolyte are capable of withstanding
the addition of oil to aqueous liquids for longer
periods of time than those viscoelastic surfactants
without the excess organic electrolyte. However,
fluorinated viscoelastic surfacta~ts are able to with-
stand the addition of oil to the aqueous liquid in
amounts up to 80 weight percent, most preferably up to
20 weight percent for a longer period of time.
The fluids which exhibit reduced friction
when used in industrial heat transfer applications are
prepared by admixing the desired amounts of the visco-
elastic surfactant and organic electrolyte to form afluid solution. Alternatively, the nonionic surfactant
lZ~35Z~
-17-
is contacted with the fluid to form an aqueous liquid
solution. The resulting solutions are stable and can
be stored for long periods of time. The fluids also
comprise additives in order that said liquids can be
employed for numerous industrial purposes. Examples of
industrial uses include distric-t heating or hydronic
heating in buildings.
The fluids employed in the process of this
invention can exhibit heat transfer coefficients over a
flow rate/temperature range which are lower than fluids
not containing the viscoelastic additives. However,
the 1uids employed in this invention exhibit heat
transfer coefficients similar to that of a fluid not
containing the viscoelastic additives at or above a
critical temperature or critical mass flow rate. Thus,
it is possible to provide a high heat transfer coefficient
in a high temperature heat exchange region, while
providing drag reduction and a low heat transfer
coefficient in the distribution lines.
The critical -temperature and critical mass
flow rate can depend on the surfactant ion structure
and the counterion concentration of the viscoelastic
surfactant. For example, longer alkyl chain length
surfactant ions and/or an excess of counterion can be
employed to provide a fluid having a higher cri-tical
temperature and critical mass flow rate than in
comparable fluid formulations. Thus, it is possible to
design heat transfer fluids which can be designed to
match the particular flow ra-te requirements and
temperature of a wide variety of heat transfer
applications.
~26~5~
-18-
The fluids employed in the process of this
invention can be employed under conditions in which
previously known heat transfer fluids ha~e been employed.
Preferred applications include those processes where
heat exchange apparatus is operated between -40C and
150C. For example, compositions can be designed in
order to match the temperature conditions and flow rate
requirements in order to achieve heat transfer in a hot
exchanger in a heating plant. However, the compositions
have the desired drag reduc-tion and lower heat transfer
coefficient in the cooler distribution lines.
The following examples are presented to
illustrate the invention and should not be construed to
limit its scope. All percentages and parts are by
weight unless otherwise noted.
In order to determine the friction exhibited
under flow conditions and the heat transfer proper-ties
of aqueous compositions, a pipe flow test loop is
prepared. The test loop comprises a pumping system, a
heating and cooling system and a testing system.
A centrifugal pump is responsible for pumping
the fluid around the loop. Its maximum output is
approximately 150 gal./min. (O.OOg46 m3/sec.) and the
dead head pressure is around 75 psi (517 kPa) gage.
The rest of the loop consists of a heat exchanger, a
mass flow meter, a test section, and a 20-gal. (0.076 m3)
expansion tank with a 3-inch (76 mm) bypass. The loop
is about 70 feet (21.3 m) long and is stainless steel.
Except for the bypass and the lines to and from the
20-gal. (O.076 m3) tank which are 3 inches (76 ~m) in
J,~35~
--19--
diameter, all the lines are 2 inches (51 mm) in diameter.
All of the valves in this loop are ball valves except
for three butterfly valves in the 3 inch (76 mm) lines
around the 20-gal. (0.076 m3 ) tank. The centrifugal
pump is capable of handling slurries and the loop
itself is built with long radius bends to reduce abra-
sion. A convenient sample size for testing in the loop
is 100 liters (about 30 gallons or 0.1 m3).
In order to prevent cavitation in the pump
during start-up and air entrapment, a 2 inch (51 mm)
diameter 3 feet (0.9 m) extension has been placed in
the 20-gal. (0.076 m3) tank. When the system is being
filled the test fluid is pulled by vacuum all the way
around the loop and then into the tank. Once the
system is filled there are no air legs in the lines.
The valve on the b~pass is closed half way when running
to divide the flow between the by-pass and the expansion
tank and allow air bubbles to escape in the-tank.
Heating and cooling the pipe flow test loop
are done by 400 lb. steam regulated to 100 psi (689 kPa)
gage and tap water using two heat exchangers. The
first heat exchanger heats or cools an intermediate
heat transfer fluid with the steam or tap water. The
intermediate heat transfer fluid is pumped to the
second main heat exchanger which heats or cools the
test fluid. The intermediate heat transfer fluid is
water containing a corrosion inhibitor. Temperature
probes are placed at the inlets and outlets of the main
heat exchanger to gather heat transfer data. A solenoid
valve is placed in the water/steam drain iine in order
to increase the pressure and, therefore, increase the
temperature in the water/steam loop. Tempera-tures of
12~35~
-20-
between 35C and 120C in the main pipe flow test loopcan be reached with this procedure.
The testing system comprises of the instru-
mentation discussed herein and a 20 feet (6.1 m) long
test section. This test section has 4-2 mm diameter
pressure taps drilled 45 cm apart near the center of
the pipe. They do not disturb the flow field in the
pipe. The entrance length from the last disturbance
before the pressure taps (the flow control valve)
exceeds S0 times the diameter of the pipe in order -that
the taps should be in fully developed turblent flow.
The two important instruments on the pipe flow test
loop are the Micro Motion Mass Flow Meter Model C200
(Micro Motion Inc.l Boulder, Colorado) and the Signature
Differential Pressure Transmitter ~odel 240B 30B ~Bristol
Babcock Inc.l Waterbury, Connecticut).
Examples 1 though '~7
Example 1 is an aqueous composition containing
0.2 percent of a viscoelastic surfac-tant of cetyltrimethyl-
ammonium salicylate prepared by admixing equimolar
amounts of cetyltrimethylammonium chloride and sodium
salicyate.
Example 2 is an agueous composition containing
0.2 percent of cetyltrimethylammonium salicylate and
0.2 percent of sodium salicylate~
Examples 1 and 2 are employed as test fluids
in the pipe flow test loop. The test fluids are initially
at 40C, 50C and 60C. The intermediate heat transfer
fluid is at 70C. The temperatures of the intermediate
heat transfer fluid entering and leaving the annulus of
3s~
-21-
the main heat exchanger and the temperature of the test
fluid entering and leaving the main heat exchangers are
measured at the different mass flow rates. The overall
heat transfer coefficient of the test fluids is calculated
using the equations:
Q=UA~Tlm=mcp~t
wherein: Q = heat transferred in BTU to the test fluid
m = mass flow rate in lb/(hr~ft2)
[Kg/(sec~mZ)]
Cp = heat capacity of the fluid in BTU/lb F
~t = temperature rise of the test fluid passing
through the main heat exchanger (t2 - tl),
ln F
U = overall heat transfer coefficient in
BT~/~lb F ft2) W/(m2 K)
A = is area of heat exchanger in ft2
~Tlm = logarithmic mean temperature drop in F
( T2 -tl ) - ( Tl t2 )
ln(T -t )-ln(Tl-t2)
T /T = temperature of the intermediate heat
l 2 transfer fluid entering/leaving the
annulus of the main heat exchanger in F
t /t = temperature of the test fluid entering/-
l 2 leaving the main heat exchanger.
Data concerning the effect of the temperature
and the mass flow rate on the overall heat transfer
coefficient U is presented in Table I.
t
--22--
~ ~ _ _ _ __ _ _ ~ _ _
o ~ o ~ ~ ~ Ln
no o~o~ ~o~
' d1 Ln ~ ~ `D ~D ~D CO CO 0
S ~ ~
~3 N
. . . . N t`
;~ N Ln O ~0 ~`
~- t~ ~ ) o ~1 o
_ ,___~ ~ ~_~
~ ~ Ln d1 ~ ~ Lr) o CO ~ C~
a) . .... . .... _
a~ dl Ln Ln Ln Ln Ln ~O dl r~ ~ ~ n
o Ei ~ Ln Ln ~o o ~ ~ ~ N
~1 3 ~ r~ ~ d' di' L ~ Lfl ~ Ln Ln ~D ~` r` ~ ~
~ X Co~Ln ~oLn
O ~ ~ O ~ ~ O ~` ~O O
C~
O O ~I Ci~ N O Ln ~1 ~ ~ ~ O C~ Lrl
~1 c:) C~l Ctl 00 ~1 ~ CO cn ~ ~I N d' d
L~
n ~ r~ -n ô o3 ~o
o -n
~ ~ ~ ~ ~ o ~ r~ c~ ~ o ~ t- ~ o
E~ . h ~ ___,~ _ ~ ___~ _ __,1 ,~
~ ~ $ ~
tlj , tl~ OO ~1~ ~ ~n Ln ~10 ~0 r` Ln ~I N ~1
a~ .~2 3 a~ N Ln ~ ~ N Lt) C` t` ~ ~) 'D ~ O
P:~ ~1 ~ r~l r-l ~1 1--l ~1 ~1 ~1 ~1 ~1 ~I r-l ~1 ~I N
,-1 ~ 1:~
~ E~ ,___~ ~_~_
S~ ~~1 ~ -- ~,lo-n~ oa),~
a~ ~ Ln~or-~ co ~<~-nco ~ON~)
~>~ ~ ~1 ~ CO e:l1 t` t` oo O O O 1~ C~ O O
O~ ~1 r~ co ~ o o ----~1
. ~ ~ _~
3 o ~ ~ ~ d~ o ,~ o o oo
a) NLn}~o ~ ~Lnl~ao~ ~OOOD
E~
o o __ ~_ ~_
X X ~Ln~lLn~o r~Lo,l-n~ r~Ln,/Ln
_~ _ t,~ I~ Ln N ~ ~t t` Ln N ~ tl'1 t` Ln N
~I ...... ...... ....
~3 O O ~I N N ~ O O ~--1 N N O O r-l N
OL~l. ___,___ _____ ____
m t~ Ln ~ ~ n ~ ~ ~ Ln
_ _ N Ln ~1 ~ ~I N ~ Ln ~1 ~ N ~n ,~
\ ~
; O O ~1 ~ N N O O ~1 ~I N O O r-l ~1
V ~
o ;:~
E~ o o o
~ u~ ~ n ~
E~
o
3S2~
-23-
The data in Table I illustrates that as
(1) the mass flow rate is increased or as (2) the
temperature, T1, is increased, the overall heat transfer
coefficient U of the fluid containing the viscoelas-tic
surfactant returns to that of water.
The heat transfer data in Table I follows the
same trend with increasing temperatures or mass flow
rate às pipe flow friction reduction data. As the
temperature is increased or the mass flow rate is increased,
a critical temperature or critical flow rate is reached
after which the fluid properties return to those of the
solvent (in this case water). The critical temperatures
and critical flow rates for drag reduction are somewhat
higher for pipe flow friction data than they are for
the heat transfer data. Since the trends are the same,
the pipe flow friction critical temperatures and critical
flow rates can be used to predict the performance of
the overall heat txansfer coefficient.
Example 3 is an aqueous composition containing
0.2 percent cetyltrimethylammonium salicylate and 0.25
percent sodium salicylate. Example ~ is an aqueous
composition containing 0.2 percent hydrogenated tallow
trimethylammonium salicylate. Example 5 is an aqueous
composition containing 0.2 percent hydrogena-ted tallow
trimethylammonium salicylate and 0.25 percent sodium
salicylate. Example 6 is an aqueous composition
containing 0.25 percent erucyltrimethylammonium salicylate,
0.125 percent cetyltrimethylammonium salicylate and 0.2
percent sodium salicylate. Example 7 is an aqueous
composition containing 0.2 percent erucyltrimethyl-
ammonium salicylate and 0.2 percent sodium salicylate.
1~635;~ ~
-24-
Fanning Friction Factors for Examp].es 1, 3,
4, 5, 6 and 7 are calculated for each composition at
different temperatures and at Reynolds Numbers between
60,000 and 965,000 using the equation:
_ D~P2
Fanning Friction Factor 4pLV2
wherein: D = diameter in cm of the circular conduit
through which the liquid is passed
~P = pressure drop in dynes~cm2 of the
liquid as it flows through the
circular conduit
p = density in g/cm3 of the aqueous liquid
L = length in cm of conduit through which the
liquid flows
15 . V = velocity in cm/sec of the aqueous liquid
The minimum Fanning Friction Factors for each temperature
are reported in Table II.
12635~
-25~
X o ~ O ~
W [~ ~ I r~ I ~ I
. , . I
,1 ,
I O ~ ~ ~D
~ ~D I ~ O O ~ ~
o o ~ ~ ,~ ,1 ~ ~ d1
~C
o
. Od'
O ~ I ~ ,~
~0 O O ~
H ~1
H X ~I d~ O O
~1 ~ ~:ld' a:~ ~ o ~ I I I I I
.
E~
~ ~ ~ o ~ I I I I
~ ~1 0
~1 ~I LO lS) Ll')
O
o
E-l u~ ~
~-~ O O O O O O O O O
d~ o ~1
E~ o
1~63S29~
-26-
The data in Table II illustrate that the
surfactant ion and excess counterion can raise the
critical temperature at which the minimum Fanning
Friction Factor is observed.
The data in Tables I and II illustrate
that the critical temperature and critical mass flow
rate depend on both the surfactant ion structure and
counterion concentration in the test fluid. Thus,
viscoelastic surfactant formulations can be designed in
order to match the temperature conditions and flo~ rate
requirements in a wide variety o heat transfer
applications.
