Power consumption of a double ribbon impeller with newtonian and shear thinning fluids and during the gelation of a iota-carrageenan solution

The power consumption of a double ribbon impeller (EKATO-PARAVISC(R)) is studied as a function of the operating conditions and the rheological behaviour of the experimental fluids. The isothermal experiments carried out with newtonian fluids gave the power curve for purely laminar and transitional flow regimes and the Kp factor was determined for the laminar flow regime. The isothermal experiments with two shear thinning fluids and the application of the Metzner and Otto concept led to the determination of the Ks factor. The experimental values of the Kp and Ks factors are in a close agreement with previous works carried on this type of equipment. The viscous behaviour of the gelling fluid (an iota-carrageenan solution) was determined with flow curves obtained under constant temperature/variable shear rate (CT/VSR) tests and under variable temperature/constant shear rate (VT/CSR) tests. The viscosities obtained with the VT-CSR tests were lower than the viscosities obtained with CT-VSR probably due to the difference in structure when the solution is gelling under shear rate. Experimental models are proposed for both viscous behaviours. The viscoelastic properties of the iota-carrageenan were characterized by using small amplitude oscillatory frequency sweeps at different temperatures. These experiments led to the determination of a gelling temperature. The experiments carried out when cooling the gelling fluid showed that the corresponding increase in the torque is quite similar to the results obtained with the theological VT-CSR tests. Moreover when applying the Metzner and Otto concept to the previously determined Kp and Ks factors and the VT-CSR viscosity models, the power consumption can be predicted with a +/- 20% accuracy. (C) 2007 Elsevier Ltd. All rights reserved.