Relation between mechanical treatment of starch and flow conditions in a scraped surface heat exchanger

Viscous products treated in a scraped surface heat exchanger receive a thermal treatment as well as a mechanical treatment. The new method developed by Mabit et al. [J. Food Engrg. 57 (2) (2003) 165] using starch as a marker for the shearing treatment was performed in order to show the influence of blades movement and flow pattern on shearing conditions. Two different flow regimes with respect to the generalised Taylor Number Ta g were investigated: a laminar regime with Taylor vortices and a weakly turbulent one. The blade rotation without scraping in the annulus space can be sufficient to apply a shear treatment above 20,000 s −1 . The product is submitted to the highest shear treatment for high rotational speed with a laminar regime with Taylor vortices. Blades scraping creates high wall shear rates, Taylor vortices improve radial mixing and renew product to be treated at the wall surface. The quantity of stressed product is directly influenced by the flow behaviour and the product residence time in the exchanger.