Orateur
Description
Many food and pharmaceutical products present a yield stress, conditioning their flow. In this study, experiments and simulations quantified the effect of yield stress on gravity-driven flow in a syringe. This flow assesses the consistency and swallowing safety of drinks. The jetting-to-dripping transition at the outlet is discussed and an expression is proposed for a critical Weber number below which dripping occurs. Rheological maps describe the interplay between rheological properties, and the volume remaining after 10s, which determines the IDDSI consistency classification. The analysis shows the dominant role of viscous dissipation for fluids classified as IDDSI levels 2 and 3, whereas yield stress has a stronger influence on less viscous fluids (level 1). Finally, a dimensionless Hydrostatic-Yield time (HY) is proposed, explaining experimental and simulation results through a mastercurve. These findings provide insights into gravity-driven flow in a syringe and the jetting-to-dripping transition. They could contribute to improving the formulation and safety of drinks for people with swallowing disorders and improving popular protorheology methods, like the syringe flow test.