Dissertation submitted in fulfilment of the requirements for the Masters Degree in
Technology: Chemical Engineering in the Department of Chemical Engineering of
Cape Peninsula University ofTechnology, 2005 / The emulsion used for this study is a new thermodynamically unstable multi-component waterin-
oil (w/o) explosive type with an internal phase ratio of approximately 94%, i.e. far beyond the
close packing limit of spherical droplets of 74%. Economic considerations and the ongoing need
for continuous drilling, loading and blasting in the mining industry, has made long-distance
pipeline transportation of these emulsion explosive systems a viable economic option. Presently,
rheological characterization of emulsion explosives is well documented (Bampfield & Cooper,
1988, Utracki, 1980). However, very little or none has been done for this system, pertaining to
the use of rheometry for prediction of pumping characteristics of these systems in long-distance
pipeline transport. This Master's dissertation is devoted to develop rheological methods of
testing, characterization and correlation in order to develop a basis for predicting the pumping
characteristics of highly concentrated w/o emulsion explosives from rheometry.
The literature and theory pertinent to the pipeline flow of high internal phase ratio emulsion
explosives are presented, as well as the fundamentals of both concentric cylinder rheometry and
pipe viscometry. The most relevant is the work of Bampfield and Cooper (1988), Utracki (1980)
and Pal (1990).
Two experimental test facilities were used for data collection. Pipeline experiments were done
using an experimental test facility at African Explosives Limited (AEL), and rheometry was
conducted at the Rheology Laboratory of the Cape Peninsula University of Technology Flow
Process Research Centre. The AEL experimental test facility consisted of a four-stage Orbit
progressive cavity pump, two fluid reservoirs, (a mixing tank and a discharge reservoir), five 45m
HOPE (high density polyethylene) pipes of internal diameters of 35.9 mm, 48.1 mm, 55.9 mm,
65.9 mm and 77.6 mm pipes. The test work was done over a wide range of laminar flow rates
ranging from 3 kg.min-I to 53 kg.min-I
. Rheometry was done using a PaarPhysica MCR300
rheometer, and only standard rotational tests (i.e. flow curve) at 30 °c in controlled rate mode
were done.
Rheological characterisation was done using three rheological models, i.e. the Herschel-Bulkley,
the Power Law and the Simplified Cross models. The coefficients obtained from these models
were then used to predict pumping characteristics. The performances of these models were then
evaluated by comparing the pipeline flow prediction to the actual pipeline data obtained from
pipeline test experiments. It was found that the flow behaviour depicted by this explosive
emulsion system was strongly non-Newtonian, and was characterized by two distinct regions of
deformation behaviour, a lower Newtonian region of deformation behaviour in the shear rate
region lower than 0.001 S-I and a strong shear thinning region in the shear rate range greater than
0.001 S-l.
For all the models used for this study, it was evident that rheometry predicts the pumping
characteristics of this high internal phase ratio emulsion reasonably well, irrespective of the
choice of the model used for the predictions. It was also seen that the major difference between
these models was in the lower shear rate domain. However, the Simplified Cross model was
preferred over the other two models, since its parameter (the zero shear viscosity denoted by 110)
can in general be correlated to the structure of the emulsion systems (i.e. mean droplet size, bulk
modulus, etc.). Thus, structural changes induced by shearing (either inside the pump or when
flowing inside a pipe) can be detected from changes in the value of the 110. The above statement
implies that Tlo can be used as a quality control measure. Different pumping speeds were found to
cause different degrees of shear-induced structural changes which were manifested by two
opposing processes. These two opposing processes were the simultaneous coalescence and
flocculation of droplets encountered at low rates of shear, and the simultaneous refinement and
deflocculation of droplets encountered at high rates of shear. These two droplet phenomena were
associated with a decrease or an increase in viscous effects, leading to both lower and higher
viscous stresses and pumping pressures during pump start-up respectively.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/912 |
| Date | January 2005 |
| Creators | Nkomo, Sithethi Espin |
| Publisher | Cape Peninsula University of Technology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/za/ |
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