Foams are ubiquitous in many industrial processes and therefore have been subjected to extensive research in the past few decades. However, a number of fundamental issues relating to foams remain poorly understood including the production and control of bubbles and how they contribute to product structure, appearance, and rheology. The work in this thesis thus sets out to study the foam rheological behaviour and its related structural evolution, to explore a potential method in controlling bubble structure during foam generation, and to introduce a novel non-invasive technique in probing foam microstructure. Foam rheological behaviour was studied by using two approaches. In a rheometric approach, the foam response to external shear and the related microstructural change, its time dependency, thixotropic behaviour and viscoelastic properties were investigated for both detergent (Gillette) and protein (egg white protein) foams. The flow curves constructed were well fitted with four-parameter rheological models, the Cross and Carreau models and revealed the true flow behaviour of foam; there was no yield stress as reported in the literature. On the other hand, the macroscopic flow behaviour of a protein foam (WPC) in straight pipes and through fittings (sudden expansion, orifice plates and perforated plates) were studied. A friction factor analysis approach which treats foam as a non-Newtonian power law fluid was successfully used to model the flow of WPC foam, this has a practical significance in that pressure drop can be calculated using a constant friction factor along a pipe of a constant cross section in any flow regime. The potential of ultrasound in controlling foam structure during the foam generation process was investigated. Depending on the types of surfactant and concentrations, ultrasound reduced the mean bubble size of foams and improved foam homogeneity. Single bubble formation in an ultrasound field managed to shed light onto the possible mechanism involved; ultrasound increased the bubble formation rate and reduced the bubble coalesce events at the nozzle. X-ray micro-computed tomography was used successfully in revealing the true three dimensional structure of some cellular/foam food products, both solid and semi liquid. Both two- and three-dimensional quantitative analyses of structural parameters were done and the spatial bubble size distribution was reconstructed using a stereology technique.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:633208 |
| Date | January 2005 |
| Creators | Sin Lim, Khai |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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