PEPT (positron emission particle tracking) is a technique for tracking a small radioactive tracer in Lagrangian co-ordinates. The technique was used to study the flow patterns of non-Newtonian CMC (Carboxy Methyl Cellulose) solutions inside a vessel agitated by an axial flow impeller. The 'non-intrusive' PEPT technique uses two position-sensitive detectors to track a radioactive particle in space and time. The particle is labelled with a positron emitting isotope. Once emitted from the nucleus a positron annihilates with an electron releasing energy in the form of two 511 keV back-to-back gamma-rays travelling in opposite directions, 180 degrees apart. The tracer particle is introduced into the stirred vessel which is mounted between the two detectors of the positron camera. Three axial flow impellers produced by Lightnin Mixers Ltd were used to carry out the experiments. Results showed that the discharge from the three impellers was radial when agitating non-Newtonian viscous solutions of CMC. Trajectory analysis was used to compare the performance of the impellers using the agitation index and the efficiency of circulation. A limited number of experiments was carried out to compare the effect of baffles on the circulation of the fluids in a mixing tank. The results showed that mixing of these non-Newtonian liquids in an unbaffled tank is better than in a baffled tank when using axial flow impellers. Other experiments were carried out to suspend solid particles in viscous fluids. Results showed that the minimum speed required to suspend large particles is lower than that required to suspend small particles. There are many correlations and models in the literature to determine the minimum speed required to suspend all the particles in a fluid; some of these correlations and models were compared with experimental results from this work. The correlation of Zweitering (1958) agreed with experimental data after modification. The Geisler et al. (1993) model agreed with the data provided that the power consumption is correctly substituted. The last part of this work concerned the flow of non-Newtonian viscous materials through industrial equipment. Yoghurt was chosen as the test fluid as one of the companies sponsoring this project was Eden Vale, a yoghurt manufacturer. A method was proposed using rheological measurements to simulate the flow through the dispensing pipeline and distributing nozzles; this method allows the designer to predict the final properties of yoghurt after passing through the paching head. Measurements were also carried out to determine the final gel structure of yoghurt in the delivery pots. This data of this thesis is useful in designing stirred tanks when non-Newtonian fluid is present, either for agitation or when suspending solids. Also, a method was provided to design yoghurt manufacturing line.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:343875 |
| Date | January 2000 |
| Creators | Fangary, Yassar Saad |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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