Le Reverend, Benjamin Jean Didier (2010)
Ph.D. thesis, University of Birmingham.
Efforts have been devoted over the last decades towards modelling phase change kinetics of fats in chocolate. The fats in chocolate have a number of crystal forms and manufacturers must deliver a product with the right polymorph to the consumer. In this work a simplifed mathematical model was developed that clusters six polymorphs into two, namely stable and unstable, depending on their Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) characteristics. This simplification allowed the phase change kinetics to be estimated from a set of DSC experiments conducted at different cooling and heating rates. The phase change reactions were coupled with the heat transfer equation and used to model temperature profiles and concentration of polymorphs in a model geometry. The model was able to predict both the temperature profiles measured by thermocouples (\(\pm\)2\(^\circ\)C ) and the fat crystals concentration as measured using XRD (\(\pm\)10%) at various locations in a chocolate slab. The model was applied to the recently developed processes using very high cooling rates such as the FrozenCone process, to explain their capabilities to produce "good" chocolate in spite of the high cooling rates used. Such modelling was not possible with existing models, which usually deal with either heat transfer or isothermal crystallisation kinetics. The main outcomes of this work are (i) the coupling of the reactions kinetics with heat transfer which can be expanded to other processes, (ii) the novel XRD method and (iii) the application to fast cooling processes and their explanation.
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