ESTiG - Artigos em Revistas Indexados à WoS/Scopus
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Percorrer ESTiG - Artigos em Revistas Indexados à WoS/Scopus por autor "Afonso, Isabel M."
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- Simulation of stirred yoghurt processing in plate heat exchangersPublication . Fernandes, Carla S.; Dias, Ricardo P.; Nóbrega, João M.; Afonso, Isabel M.; Melo, Luis F.; Maia, João M.In the present work, simulations of stirred yoghurt processing in a plate heat exchanger were performed using computational fluid dynamics (CFD) calculations and the results compared with experimental data, showing a very good agreement. A Herschel–Bulkley model for the viscosity and an Arrhenius-type term for the temperature dependence were used to model the thermo-rheological behaviour of yoghurt. The heat exchanger used in this study operates in a parallel arrangement, thus simplifying the problem to the construction of a single complete 3D channel. After analysis of the velocity field and fanning friction factors, laminar flow was observed for all the operating conditions used and relations are proposed for the present heat exchanger between fanning factors and Reynolds number and between mean shear rate and mean velocity of yoghurt.
- Thermal behaviour of stirred yoghurt during cooling in plate heat exchangersPublication . Fernandes, Carla S.; Dias, Ricardo P.; Nóbrega, João M.; Afonso, Isabel M.; Melo, Luis F.; Maia, João M.In this study, CFD calculations were made in order to analyse the thermal behaviour of yoghurt in a plate heat exchanger, the yoghurt viscosity being described by a Herschel-Bulkley model. The influence of Reynolds number on local Nusselt numbers was analysed as well as the influence of entry effects on average Nusselt number. Numerical runs considering and discarding the influence of temperature on the viscosity were performed and the impact on average Nusselt numbers was analysed. Transversal variations of viscosity were studied and thermal correlations including the ratio between bulk and wall viscosities are proposed. The obtained thermal correlations were compared with the experimental ones (described in the literature) and a very good agreement was found, mainly when considering the effect of temperature on viscosity. Simulations with a non-Newtonian fluid having lower Prandtl numbers than yoghurt were performed in order to analyse the influence of this variation on the Reynolds number exponent of the thermal correlation.