TWENTY-SIXTH CONFERENCE
VISCOSITY FO
By P. G. ATHERTON
Introduction
At Kalamia a new set of A and B molasses pumps was installed
for the 1958 crushing season. The molasses from the high grade
centrimgals is diluted before entering the inlet to these pumps and in
order to ascertain the viscosity of molasses presented to the pumps under
various conditions of dilution, an investigation into the relationship
between brix and viscosity of A and B molasses was carried out. The
results were found to show a high degree of regularity and the investigation was extended to include syrup and final molasses.
Apparatus and Procedure
Samples of syrup were taken from the pump outlet to the pan
stage, A and B rnolasses from the fugal gutters before dilution and t h e
pump delivery after dilution, and final molasses from the fugal gutters.
The samples were carefully mixed, a portion placed in the viscometer
cup and a second portion diluted 1 : 1 and the brix determined by spindle.
The viscosity of the sample was determined without deaeration a t a
temperature of 50" C. using a Technico torsion wire viscometer described
by Kelly and McAntee [2]. This viscometer is fitted with a waterjacketed cup through which water was circulated by means of a
gear pump from a thermostatically controlled bath. The temperature of'
50" C. was chcsen as this is approximately the average temperature a t
which syrup and molasses are pumped. The viscosity was determined
as soon as temperature conditions were steady and without any attempt
a t deaeration as the viscosity of the material actually being pumped
was desired.
The first series of samples was taken early in the 1958 season while
a second smaller series was taken at the end of the season to ascertain
any changes caused by alteration to the nature of the material being
handled.
Results and Conclusions
The results are shown in graphical form in Fig. 1, 2 and 3. Figure 1
shows a graph of viscosity a t 50" C vs. brix for the first series of tests.
The graph shows a gradual increase of viscosity with brix up to approximately 80 brix. Between 80 and 90 brix, the rate of increase becomes
larger and above 90 brix, viscosity increases very rapidly with brix.
I t can be seen from the graph that the brix values for syrup, A molasses
and B molasses overlap but the viscosity values still lie on the same
smooth curve. Thus it would appear that the viscosities of these samples.
are fairly independent of the purity of the material, a t least down to
about 55 apparent purity. This agrees with the work of King [3] on
46
TWENTY-SIXTH CONFERENCE
1
zoo
*Syrup
0 A Molasses
Fig. 1-Viscosity
at
50" C.vs. brix.
cane molasses in the Philippines who found that down to approximately 45 true purity, purity had little influence on viscosity. King
carried out viscosity and concentration determinations on composite
molasses from twelve Philippines factories and found a relationship
similar to that disclosed by the present tests. Due to the non-linear
form of the simple viscosity brix graph, no simple equation can be
written for the relationship. Several investigators have used different
co-ordinates to obtain linear relationships. Silin and Silina [5] working
with raw beet molasses and Zelikman and Abdullaev [B] using refinery
Brix
beet molasses found that plotting logarithm viscosity against
100 - Brix
gave a linear relationship. A plot of the results of King (curve B)
and the present series of tests (curve A) on this basis is shown in Fig. 2.
I t can be seen that the relationship is not linear over the whole range.
Over a limited range of brix values from approximately 83 to 88 the
graph is linear, but above and below these values the graph becomes
curved. The difference between these results a t the ends of the range
and those of Silin [5] and Zelikman [B] cannot be checked as the
range of brix ~ ~ a l u over
e s which these investigators worked is not stated
in the references. Also the fact must be considered that beet molasses
is known to have a different chemical composition from cane molasses;
for example, beet molasses contains a very low proportion of invert
sugars and also some raffinose.
TWENTY-SIXTH CONFERENCE
Fig. 2-Comparison
Fig. 3-Log
of results at Kalomia and those of King in the Philippines.
viscosity at 50" C. vs. brix, showing transition points.
48
1959
TWENTY-SIXTH CONFERENCE
Further investigation of logarithmic plots showed that a direct plot
of log viscosity as. brix, for the results gave a graph with two straight
lines intersecting in a transition point, as shown in Fig. 3, curve A.
A similar plot of the results of King gave a graph of the same
form shown in Fig. 3, curve C. I t will be seen that the results of
King show much higher viscosities than those reported at Kalamia;
however, King's work was carried out a t 25" C,., which makes direct
comparisons of viscosity impossible. A curve of temperature us. viscosity
in King's paper shows that the viscosity would decrease about tenfold
from 25 to 50' C., which means that viscosities are of the same order
as those of the present series.
Curve B in Fig. 3 shows the results of the second series of tests
which was performed at the end of the season. The curve shows the
same form as curve A with lower riscosities for the lower brixes with
the difference decreasing as the brix increases. This difference would be
due to a change in the nature of the material from the beginning to the
end of the season.
The two straight lines of different slopes in each case indicate that
above the transition point the increase in viscosity with brix is much
more rapid than below it. The transition point occurs at approximately
83.5 brix in curves A and l3, and 87.5 brix in curve C. The equations
to these lines are of the form:Log -q = M.Bx. 4- c
where 7 = viscosity
PIf = slope of line after correction for scales
C = a constant which represents the intercept on
the viscosity axis when Rx. = 0.
MBx.
17 = Ke
where K = a constant = ec.
The slopes of the various lines, which are also the indicies in the equation,
have been calculated and are shown in Table 1.
:.
TABLE I
Index M
Material
Low brix
/
-
High brix
Transition
brix
Kalamia (start of season)
Kalamia (end of season)
King (Philippines)
..
I t will be noted that the indicies for Philippines molasses are much
higher than those for Kalamia, which indicates that the Philippines
material was more sensitive to changes in brix.
The lines at Kalamia for the beginning and end of the season, while
being displaced from one another and thus having a different K, do not
vary a great deal in slope and an average slope of 0.118 for the low
brix index and 0.278 for the high brix index would be sufficiently accurate
for most calculations. Thus, by knowing the viscosity at any one brix,
the position of the transition point and the slopes of the lines, the viscosity
at any other brix can be calculated.
1959
TWENTY-SIXTH CONFERENCE
49
The theoretical reason for the transition point is another point of
interest. Several possible causes can be considered and discussed, viz.;
1. The existence of grain in the higher brix samples.
2. Increased aeration.
3. The onset of saturation.
4. The natural effect of increased concentration.
1. Samples above and below the transition point were examined
microscopically and apart from a small quantity of large grain, which
had obviously come through the fugal gauze, no appreciable amount of
grain was found in any of the samples.
2. A sudden increase in the viscosity characteristic due to increased
aeration is not likely as it would be expected that any increased tendency
to aeration would be gradual.
3. With regard to the transition point being caused by the concentration reaching the saturation point, Doss, Gupta and Vishnu [I] state
that a break in the viscosity curve has been found when molasses is
cooled through the saturated condition. If so, this would also be
expected when molasses passes through the saturation point by increasing
concentration., However, neither Micheli aud De Gyulay 141 or Kelly
and McAntee 121 working with Australian molasses, found a transition
point when cooling through the saturation point. I t also seems unlikely
that this would be the cause of the transition point in this case as both
A and B molasses exhibit the same brix a t the transition point while
the sucrose concentrations would be quite different ; for example :A molasses at 83.5 Bx. and 63 purity.
Pol = 51.8. Water = 16.5 approx.
Po1/100 water
= 314.
B molasses at 83.5 Bx. and 55 purity.
Pol = 45.9. Water .=. 16.6 approx.
Pol/100 water
.= 278.
which shows a difference of more than 10 per cent. in concentration.
4. The view that the transition point is a concentration effect
caused by internal cohesion seems more likely. King calibrated his
viscorneter using pure invert solutions a t different concentrations and
found the same type of viscosity-concentration relationship as has been
found for molasses. As the invert solutions were deaerated and free
from crystal, the influence of crystals and aeration can be discounted
and, from the work of Micheli and De Gyulay and Kelly and McAntee,
saturation seems an unlikely reason for the transition point.
Such serni-log or log-log relationships with transition points are
quite commonly found in experiments with naturally occurring materials
and it seems likely in this case that the transition point is not caused
by any heterogeneity of the material or by the onset of saturation, but
is due to an increase in internal cohesion.
The practical application of the transition point, which marks the
onset of the steep increase in viscosity with brix, can be seen when
considering the pumping of A and B molasses back to the pan s t q e .
Molasses from the centrifugals is usuallj7 diluted before pumping for
purposes of sugar boiling and this dilution also eases the load on molasses
I
50
TWENTY-SIXTH CONFERENCE
T 959
pumps. In order to feed a material of fairly uniform viscosity to the
pumps, dilution should be controlled in such a way as to avoid wide
fluctuations in brix as, if the upper region of the brix values is above
the transition point, small increases in brix will cause large increases in
viscosity. These in turn will cause variations in pump capacity and
may even lead to failure of the pumps to handle the output of molasses.
A further and probably more important application of the results
is that, once the relationship has been determined, it enables the viscosity
of the molasses at any known brix to be predicted within reasonable
limits of accuracy.
Acknowledgments
The author wishes to express his appreciation to the Management
of The Australian Estates Company Limited, for permission to publish
this paper.
REFERENCES.
[I] Doss, K. S. G., Gupta, S. L. and Vishnu: 1956. "Electrolytic Conductance
of Molasses in relation to Saturation Temperature." Sugar Industry
Abstracts, 18, p. 88.
[Z] Kelly, F. H. C. and McAntee, 8.: 1942. "The Viscosity of Rlolasses and
Massecuites." Proceedings Q.S.S.C.T. Thirteenth Annual Conference,
p. 51.
[3] King, R. H.: 1933. "Viscosity of Impure Cane Sugar Solutions." I.S. J.,
35, p. 187.
[4] Micheli, L. I.A. and De Gyulay, O.S.: 1938. "Viscosity-Supersaturation
Relationship of Industrial Sugar Solutions." Proceedings I.S.S.C.T. Sixth
Congress, p. 1094.
i5j Silin, P. M. and Silina, 2 . A,: 1954. "Viscosity of Molasses." I S . J., 56,
p. 116 (Abs.).
[ti] Zilikrnan, I. F. and Abdullaev, T. A.: 1958. "Viscosity of Refinery
Molasses." Sugar Industry Abstracts, 20, p. 66.
Kalanaia Estate,
Ayr.