Viscosity of chia seed water suspension using two mixers and two approaches

Abstract

Two commercial mixers, four-blade (vane) and six-blade, attached to a rheometer were tested to evaluate the viscosity of a chia seed water suspension using radius ratios of 1.4 and 1.2, respectively, in the mixer-in cup systems. Two approaches were proposed to calculate the effective and shear viscosities, power consumption in laminar flow, and Couette analogy. The relationship between the power and Reynolds numbers gives a proportionality constant of 6.27 for the four-blade mixer and 5.19 for the six-blade mixer. The effective viscosity was estimated using the respective constant, measured torque, and angular velocity. Sodium carboxymethylcellulose solutions were used to validate the Couette approach. The shear rate was calculated considering Newtonian and shear-thinning behaviours. The effective viscosity of chia water (10% seeds) varied from 4.46 to 2.43 Pa s for a range of 100–300 rev min−1, while the shear viscosity varied from 3.26 to 1.81 Pa s for a range of 60.1–180.2 s−1. The flow behaviour index was 0.45, and the consistency index was 22.1 Pa sn. Results are useful for quality control purposes and for design calculations. A practical procedure was performed to calculate shear viscosity and shear rate, using the four-blade mixer, helpful for rheological characterization of coarse suspensions.