31311*11
CHIEF
technische
Hogeschool
OF THE N.S.M.B.
/kik
ppl. Sci. Res. 29Delft
June 1974FRICTION REDUCTION
AND DEGRADATION IN TURBULENT FLOW
OF DILUTE POLYMER SOLUTIONS
J. H. J. VAN DER MEULEN
Netherlands Ship Model Basin, Wageningen,
THE NETHERLANDS
Abstract
An experimental study of friction reduction and polymer degradation in turbulent pipe flow is described for dilute water solutions of guar gum,
CMC, Separan NP-10 and Polyox WSR-301. The tests are made in a
tur-bulent-flow rheometer with a 2 mm I.D. pipe over a Reynolds number
range from 8,000 to 25,000. The maximum attainable friction reduction for guar gum, Separan NP-10 and Polyox WSR-301 is found to be almost equal, but large differences in effectiveness occur. The most effective polymers
(Polyox WSR-301 and Separan NP-10) are also the most liable to degra-dation. Mixing of polymers does not ameliorate the maximum friction re-ducing ability of the most effective component.
§ 1. Introduction
In 1948 Toms [1] published data on the flow at large Reynolds numbers of solutions of polymethyl methacrylate in
monochlor-benzene through straight tubes. He found a remarkable increase of the flow rate at constant pressure gradient when the polymer was added to the solvent. This phenomenon of turbulent-flow friction reduction has been observed to occur for a large number of
differ-ent polymers and solvdiffer-ents. Most of the relevant studies are
con-cerned with the friction reduction of polymer solutions in water. It seems that the mechanism of friction reduction cannot be
ex-plained by a reduction of the viscosity due to shear thinning. On
the other hand, it is generally accepted now that macromolecules
increase the thickness of the viscous sublayer. This concept is further supported by the experiments of Rudd [2] who measured velocity profiles in a polymer solution by using a laser
t
LI. tT
toctnxiort
162 VAN DER MEULEN
,
33IN
e"4%-41A
meter. Yet, the interaction of macromolecules on the turbulence in a flow is still poorly understood.
In addition to friction reduction, polymer solutions are also able to reduce flow noise [3] or suppress cavitation [4, 5, 6]. The friction-reducing ability of specific polymers has been investigated exten-sively. In a comprehensive review paper, Hoyt [7] treated among
others the turbulent pipe-flow properties of a number of impor-tant polymers. It appears, however, that Only a few papers deal
with comparative tests. Besides, degradation properties Are scarcely given.
In this paper, the friction 'reduction and degradation properties of four polymers are compared to :each- other in a broad range of
concentrations of the solution. In addition, the paper deal i with
handling, mixing and viscosity measurements. § 2.. The turbulent-flow rheometer
To study friction reduction and degradation of polymer solutions,
a turbulent-flow rheometer has been devised. In the rheometer a
fluid sample is forced to flow through test pipe at constant
ve-locity. The pressure difference across the test pipe is measured by
which friction reduction is determined. The rheometer shows a
close resemblance to the one first described by Hoyt [8]. In
accor-dance with the rheometer used by White- [9], the velocity in the
test pipe can be varied.
A schematic diagram of the rheometer is shown in Fig: A
1/3-horsepower rotary-current motor with a maximum rpm of 4500. is
connected to an electromagnetic clutch and brake. A worm gear reduction unit reduces the rotational speed with a factor 7.5 and
provides the axial movement of the piston. A fluid sample With a vohune of 184 cc is stored in the cylinder. When the piston moves upwards, the fluid is forced through the test pipe. The test pipe has
a length of 800 mm and a.n internal diameter of 2 mm, the en-trance being well rounded off. The 'pressure in the cylinder is
measured by one of two precision manometers ,,(range 0-4 kg/crn2
and 0-10 kg/cm2). ,,
The rheometer is. provided with a ,filling cup and an auxiliary
larger diameter filling pipe. The bottom part of the cylinder is con-nected to a drain-cock, which is used for rinsing the interior of the
TEST 'PIPE APm_WAY FILLING:POE .,DRAIN COCK FILLING CUP MEMBRANE PRECISION MANOMETERS 1.* ELECTRO-MAGNiTIC CLUTCH AND BRAKE
KIPA.MIE
1GEA BOX
Fig
'
I . Schematic .diagram of turbulent flow rheometer.
; \
speed of the motor is adjusted and tiekt;thei,electiortiagnetiC. Clutch is ;switched6on..,Pue,,to an accurate .feed-back speed control of the motor, the Upward velocity of the piston remains Constant through; out the _cylinder height covered.
The measurements provide data on the friction, factor in the test pipe as function of the Reynolds number. The energy balance gives.
:L N
=
ipV2(1+IT-) )
where dRis the total pressure differente across test the pipe, p is the liquid density,: Vi:isthe yeloeity in the test pipe, C,isthe entrance loss:,
coefficient, f is the friction factor (according to Moody [10]), L is the length and D is the internal diameter of the test pipe.
For water, the coefficient 4- is about 0.1. This value may be
influ-enced by rheological effects in the entrance part of the test pipe
when polymers are used. Since LID = 400, the value of is small
compared to the value of
1 ± f LID (f 0.01-0.03). For thisreason, the rheological effect on was neglected.
Throughout this paper, the Reynolds number is based on the dynamic viscosity of pure water, which is a function of the
tem-perature only. The Reynolds number was varied between 8,000 and
25,000. For water, these values lie well in the turbulent-flow
re-gion. Castro and Squire [11] and White and McEligot [12] found
that polymer solutions in water cause a delay in turbulent transi-tion. On the other hand, Paterson and Abernathy [13] found that
for low-disturbance pipe inlet conditions, polymer solutions
under-go turbulent transition at lower Reynolds numbers than the pure
solvent.
Particulars of polymers
Four important high molecular weight polymers have been tested: guar gum, CMC, Separan NP-10 and Polyox WSR-301. Guar gum
is a natural product; its origin is from the guar bean grown in
Pakistan, India and the Southwest United States. The trade nameof the guar gum tested is Solgum 3H0. Its composition in weight per cent is: galactomannan 81.2, moisture 10.5, protein 5.0, fibre
1.7, ash 0.9 and fat 0.7. The trade name of the CMC tested is
AKU-CMC, Type HZ 555 (Algemene Kunstzijde Unie). Its compo-sition in weight per cent is: sodium carboxymethylcellulose 92,
so-dium chloride 1.2, soso-dium glycolate and soso-dium acetate 0.8 and
water 6. Separan NP-10 (Dow Chemical) is the trade name of
poly-acrylamide. Its molecular weight is about one million. Polyox
WSR-301 (Union Carbide) is one of the grades of poly (ethylene oxide) which have a molecular weight of several millions.
Preparation of stock solutions
To prevent degradation due to shear stresses, stock solutions have
to be prepared carefully. In the literature details on preparation are scarcely given. Quite a few tests had to be made before the
(tempera-ture 20°C) are put in a 5-litre pyrex glass beaker. The water is stirred by a three-bladed propeller (diameter 5 cm) driven by a 1/30 hp dc motor. To obtain a stock solution of 2500 ppm (parts per million by weight), 5 g polymer was slowly sifted into the water. The number of revolutions and the mixing time for each
polymer are given in Table I.
TABLE I
Mixing time and number of revolutions for preparation of stock
solutions.
Guar gum solutions are subject to deterioration by bacteria. To
prevent this, formaldehyde to a concentration of 500 ppm was added to the stock solution. The properties of the CMC solution
are not much influenced by the mixing time or the number of revo-lutions. Reducing the mixing time to 5 min led to the same results.
The properties of the Separan NP-10 solution do depend on the
mixing time.
After a mixing time of h, the particles were not completely dissolved yet. For Polyox WSR-301, a reduction of the mixing time to I h did hardly influence the results. Another satisfactory
method to prepare a Polyox WSR-301 solution is to sift the powder into the water and let it rest for 16 h.
Some tests were made to estimate the stability of the stock
so-lutions. It was found that all solutions could be stored for at least
three days except for Separan NP-10 which could be stored for
two days only. § 5. Viscosity
When a polymer is dissolved in water, the viscosity of the solution is both a function of the polymer concentration and the shear rate.
To measure the viscosity as a function of polymer concentration for laminar flow, a capillary viscometer type ASTM 0 was used.
Guar gum 1 1600
CMC 1 1700
Separan NP-10 1 1500
Polyox WSR-301
i
1500Polymer Mixing Time, Number of
a. v-10 C MC Guar gum Polyox WSR-301 Separan NP-10 0.8 0.8 0.4 0.2
--I
Ii
_ 5 10 20 50 100 200 500 1000 Polymer concentration, ppmFig. 2. Effect of polymer concentration on viscosity
(zip= nsolution nwater)
The results for the four polymers tested are given in Fig. 2 where
An(= nsohition ')water) is plotted against the polymer concen-tration. The measurements were made at a temperature of about
20°C and a mean shear rate of about 1000 s-1. When such
measure-ments are carried out very accurately and the results are
extra-polated to zero shear and zero concentration, the intrinsic viscosity. is found and the molecular weight of the polymer can be calculated
[14, 15].
§ 6. Friction reduction
The friction factor / has been measured as function of the Reynolds number for concentrations of 2, 5, 10, 20, 50, 100, 200 and 500 ppm. For Polyox WSR-301 the range was extended with concentrations
of 0.1, 0.2, 0.5 and 1 ppm. To avoid degradation, a fresh sample was used for each measurement made with Separan NP-10 and
Polyox WSR-301. With guar gum and CMC, a fresh sample was
used for several measurements. The results are given in Figs. 3
through 6. In these figs the friction factor measured for pure water and the friction factor for laminar flow are included. In Fig. 7
0.03 0.01 c0 Water AP.0 coo
,
co e044440o oo cvpctici
c..._ a &a"
"Ofia._ ID go &AAaa. 'OM4 a Biaa MO =di *v ME o 2 ppm 50 ppm°:
AS 100 -p 10 200 20 500 0.0061 1 1 1 1111E11111 ' 6 10 15 20 25 30 Reynolds NumberFig. 3. Effect of Reynolds number on friction factor for guar gum solutions in water.
10 15 zo 25 30
Reynolds Number
Fig. 4. Effect of Reynolds number on friction factor for CMC solutions in
water.
0.0066 10 15 20 25 30 Reynolds Number
Fig. 5. Effect of Reynolds number on friction factor for Separan NP. 10
solutions in water. 0.03 0.02 0.04 Water o 2 ppm 50 ppm 64 45 _ 100 - Tri 010 200 20 500 1 1 1 1 1 1 1 1 1 1 0 0 80 0 0 0ocb000 mom moo -£4 a A a AAA& 00.1441:040060.1644° 0 _ V 0 0 _
00 0a
oacoarzooaaccP _ v, _: ;vile
viv,
_ _ # it &... a :vVIAMWV V VV"VVV777 -_ :15. VVv, -A1 ale,, Iftw%MIN
VV. 64 / Te-1 1 I I I I I 1 1 1 e Water o o o eG000000 oo 090990°Gookioes o099 fite00140110 o SO OS it, 0 0 03 000" . 4° if e:
VT P Amt... CFra.ao-.oaajLoo
C041:111°Altr4V. 0 1:17 ni Lr°00 *Oak41 v., 01 ppm 13 10 ppm %IA, 90.2 20 0.5 50 (1 100 02 200 AS 500 1 1 1 1 1 1 1 1 15 20 215 Number 10 ReynoldsFig. 6. Effect of Reynolds number- on friction factor for Polyox WSR-301
) solutions in water. 0.04 1 1 1 1 1 1 1 1 1 1 1 0.03 0.02 0.01 0.0066
%.a co eels $61.2,, 6.4 130. 44.1,,' 014% 64kAsoa °Igh '2413..tql 200 ppm Guar gum + 20 ppm Polyox W512-301 A 200 ppm Guar gum 020 ppm Polyox WSR -301 10 15 20 25 30
Reynolds Number xlci3
Fig. 7. Effect of Reynolds number on friction factor for mixture of guar gum and Polyox WSR-301 solution in water.
tion factor results are given for a mixture of 200 ppm guar gum and 20 ppm Polyox WSR-301, and for each constituent. A fresh
sample was used for each measurement made with this mixture.
§ 7. Degradation
Many investigators indicated the fact that polymer solutions are
liable to mechanical breakdown or degradation due to high shear stresses. Degradation depends on the type of polymer, its
concen-tration, the value of the shear stresses and the time during which
the polymer is subjected to shear stresses. Paterson and Abernathy
[15] reported on degradation tests made with several grades of
poly (ethylene oxide).
Hoyt [8] presented some degradation data for Polyox WSR-301
and guar gum, obtained by repeated tests of the same solution in
the turbulent-flow rheometer.
The same procedure was used in the present investigation. For each sample, 20 test runs were made and after each test run the sample flowed back in the cylinder by the auxiliary filling pipe.
Tests were made at two rotational speeds of the motor (2500
0.04 I I I I I
II
I I 1 1 water 1 1 1 0.03 0.02 C 0.01 0.006and 3600 rev/min) corresponding to Reynolds numbers of about
16,000 and 23,000.
The amount of degradation 6 and the friction reduction e are
given by
an =
6 - en
x100%
/water - /solution
X 100% /water
where the subscript n stand's for the number of test runs made (the subscript 1 is omitted). The results of the degradation tests
are given in Tables II through V.
In some cases, negative values of a were found which means that the friction reduction increased during the test.
TABLE II
Concentration Re
s820
PPm per cent per cent per cent
Friction reduction e and amount of degradation 8 for guar gum.
500 16000 63.0 23800 67.5 0 1.0 200 15600 59.2 1.0 2.2 22500 61.0 5.2 9.0 100 15800 47.8 1.3 3.1 22500 51.2 11.7 17.8 50 16100 36.3 3.6 7.2 23000 38.1 18.6 28.3 20 16000 21.8 5.5 11.9 23300 20.6 23.3 37.4 10 16500 11.7 14.5 21.4 24000 11.4 30.7 44.8 5 16600 7.0 29 37 24000 7.4 46 58 2 17000 2.9 65 76 24000 2.6 50 62 and
=._-500 16000 33.9 23000 37.7
TABLE III
Friction reduction s and amount of degradation 8 for CMC. TABLE IV
Friction reduction e and amount of degradation 8 for Separan NP-10.
Concentration PPm Re 8 per cent 82 per cent sio per cent 500 17400 56.1 -5.0 -7.5 24700 61.3 -4.2 -6.2 200 16500 62.1 -1.1 -1.1 24500 66.2 -0.8 4.2 100 17100 64.3 0 7.9 26500 67.5 0.7 23.7 50 18100 64.7 4.0 25.3 26500 66.0 11.4 41.3 20 18200 54.2 12.7 40.2 25400 50.6 20.4 58.0 10 17200 40.4 17.1 49.3 26000 34.4 26.1 66.6 5 17000 26.9 24.1 62.8 25000 20.0 35.5 71..5 2 18300 13.6 41 71 25100 7.5 40 76 Concentration Re 8 820
PPm per cent per cent
200 16000 22.2 23000 23.4 100 16000 14.1 23000 15.7 50 16000 8.6 23000 8.6 20 16000 4.4 23000 5.1 10 16000 2.9 23000 3.7 5 16000 1.5 23000 1.8
TABLE V
Friction reduction E and amount of degradation 8 for Polyox WSR-301.
§ 8. Discussion
By comparing the results of the friction factor measurements (Figs.
3 through 6) it appears that the maximum attainable friction
re-duction for Polyox WSR-301, Separan NP-10 and guar gum is al-most equal. Yet, a large difference in effectiveness is found. Polyox WSR-301 is by far the most effective, a concentration of 20 ppm
gives about the same friction reduction as a concentration of
100 ppm Separan NP-10 or 500 ppm guar gum. A concentration of 0.1 ppm Polyox WSR-301 already shows a slight deviation from
the pure water curve (Fig. 6). Guar gum displays a continuously
increasing friction reduction with increasing concentration, while for Polyox WSR-301 and Separan? NP-10 the maximum friction
reduction is attained at an intermediate concentration. The fric-tion reducing ability of CMC is much smaller than for the other
polymers tested. As shown in Fig. 7, mixing of polymers does not ameliorate the maximum friction reducing ability of the most ef-fective component.
Concentration PPm
Re
per cent per cent per cent
500 16700 53.2 -2.1 -6.2 23800 58.7 -1.9 -4.1 200 17200 58.4 -2.2 -5.1 23800 62.9 -2.2 -2.1 100 16800 60.6 0 0 24500 66.0 -0.6 10.9 50 17200 63.3 1.3 9.2 24000 67.5 1.6 26.8 20 16700 64.0 2.5 27.6 23700 67.6 6.4 46.6 10 17500 64.6 10.5 46.8 25200 63.8 23.7 64.9 5 16900 57.1 21.2 57.5 25000 50.0 30.6 71.8 2 17900 36.5 26.8 68.2 23900 28.2 41.2 77.6
A comparison of the present friction factor data with other data
mentioned in the literature is complicated by the fact that the
friction reduction is also affected by the pipe diameter, which may range from 0.6 mm [9] to 25 cm [16]. Besides, there are variations in polymer composition due to differing blend numbers and due to changes in specification for the same designation. Qualitively,
how-ever, the friction factor results are in agreement with those
re-viewed by Hoyt [7].
The results of the degradation tests (Tables II through V) show
that the most effective polymers (Polyox WSR-301 and Separan NP-10) are also the most liable to mechanical breakdown. Guar
gum is somewhat more stable in this respect but still shows appre-ciable degradation. CMC is very stable, it does not show any degra-dation. For large concentrations of Polyox WSR-301 and Separan NP-10 negative values of the amount of degradation 6 are found. To explain this anomaly it should be realized first that friction re-duction depends strongly on the concentration of the highest molecu-lar weight species present in the solution [15]. Ruptured molecules
will probably not contribute to friction reduction. When a
solu-tion with a large polymer concentrasolu-tion is subjected to high shear
stresses,
severe degradation will occur and the re- maining
solution will show a considerably reduced concentration of the
highest molecular weight species. This means that the remaining solution will behave as a solution with a low concentration of un-broken polymer molecules. According to the results given in Figs.
5 and 6 this will produce a larger friction reduction and,
conse-quently, a negative value of 6. The large values of 62 for Polyox WSR-301 and Separan NP-10 which are found for low
concentra-tions (Tables IV and V) indicate that the results of the friction
factor measurements for low concentrations of these polymers (Figs. 5 and 6) are influenced by degradation in the test pipe. This degra-dation effect becomes less severe when the Reynolds number (and thus the shear stress) decreases.
In the literature it has been stated that polyacrylamide has a 'reasonable' resistance against degradation [17] and guar gum is
described as 'extremely stable' [7]. The present results contradict these statements.
: Acknowledgement - , ,,c, The research reported in this p,aper,was conducted at the Nether-lands ,,Ship. Model. Basin and sponsored by the Royal NetherNether-lands
Navy,: those shipyards:participating:in the Netherlands United
Shipbuilding,p4raux Ltd.,.arid,Lips;N.V..Propeller Worl5s.
Received 12 April 1973
In 'final form 4 July 1973
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