Entrance flow of unfoamed and foamed Herschel-Bulkley fluids

The present study investigates extrusion processing of unfoamed and foamed cocoa butter (CB) crystal-melt suspensions (CMSs) with varying crystal volume fraction FSFC. Capillary rheometry derived flow curves were fitted with the Herschel-Bulkley-Papanastasiou (HBP) model, and the derived yield stress to wall shear stress ratio tau(0)/tau(w) of CB CMSs was compared for the various FSFC. Foamed CB CMSs behaved fluidlike for Phi(SFC) <= 11:9% and according to a brittle porous solid for FSFC. 11:9%. The dimensionless entrance pressure loss nen=a as a function of dimensionless shear stress t* was higher for foamed compared to unfoamed CB CMSs at Phi(SFC) <= 11:9% and lower for foamed compared to unfoamed CB CMSs at Phi(SFC). 11:9%. The FSFC dependent difference in n(en)/alpha was attributed to the crystal confinement in the die entrance flow, which is increased in the case of elastic gas bubble deformation and decreased in the case of plastic gas pore collapse. The computational fluid dynamics simulated flow of unfoamed and foamed CB CMSs through an abrupt circular 20:1 contraction with the HBP model was compared with the experimental results from quantitative entrance flow visualization (QEFV). Furthermore, the QEFV derived half center incidence angle. as well as the entrance flow shear and elongational rates gamma(over dot)(ef) and epsilon(over dot)(ef) were derived and used to establish a model predicting the Bagley entrance pressure loss Delta P-Bag and calculate an entrance flow characteristic shear and elongational viscositiess eta(ef)s and eta(e)(ef). (C) 2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution