Aeration and rheology of viscoplastic bubbly liquids generated in a planetary mixer

Planetary mixers are widely used to aerate viscous fluids to generate bubbly liquids from the bench to factory scale. The aeration of two aqueous commercial Carbopol solutions (2.1 and 1.1 wt%) at room temperature and pressure was studied in a bench-scale mixer and the evolution of air volume fraction ϕ and bubble size distributions quantified. In most cases the aeration dynamics followed the simple model of Fernandes et al . (2024) well, with aeration rate and bubble disengagement parameters exhibiting different dependencies on the maximum wall shear rate. More complex lumped parameter models did not offer significant improvements in accuracy. The bubble size distributions were consistently log-normal and did not change markedly during aeration: larger bubbles retained ellipsoidal shapes generated during aeration. The rheology of bubbly liquids with volume fraction ϕ < 0.40 was studied at length: these exhibited elasto-viscoplastic behaviour, as reported elsewhere, with scaled bulk elasticity, elastic limits, and Herschel-Bulkley fluid parameters (when flowing) exhibiting a consistent linear dependency on ϕ , indicating that the volume fraction of the continuous phase determined the material’s response to shear. • Aeration of aqueous Carbopol TM suspensions exhibits asymptotic approach to ϕ max • Simple model based on air incorporation and disengagement captures observed behaviour • Bubble size distributions are log-normal with non-spherical larger bubbles • Bubbly Carbopols exhibit elasto-viscoplastic behaviour • Scaled rheological parameters found to vary with 1- ϕ