RHEOLOGICAL CHARACTERIZATION OF SUSPENSIONS OF SUCROSE CRYSTALS IN SATURATED SUCROSE SOLUTIONS

Abstract

ABSTRACT Suspensions formed by saturated sucrose solutions were analyzed at different temperatures (0 ≤ T ≤ 65C) and with different added fractions (0.005 ≤ φ ≤ 0.40) of known size sucrose crystals (0.163 ≤ dp ≤ 1.26 mm). Saturated sucrose solutions, taken as the suspension dispersant mean, were rheologically characterized using a concentric‐cylinder rheometer and showed Newtonian behavior. The crystal suspensions were rheologically evaluated by using a mixer‐type rheometer constituting an anchor impeller coupled to a rotational rheometer, also known as a mixer‐type rheometer. The studied crystal suspensions also showed Newtonian behavior. Theoretical and semiempirical models were used to describe the correlation between suspension relative viscosity and crystal volumetric fraction. The best results were obtained using the Krieger and Dougherty, and the Mooney model, resulting in values of intrinsic viscosity, (η), and maximum packing fraction, φm, compatible with data reported for coarse concentrated suspensions of nonspherical particles.PRACTICAL APPLICATIONSRheological follow‐up of dynamic systems may be useful for a wide variety of applications where there is a manifest interest in studying the rheological evolution of a medium under controlled conditions. In crystallization processes, nucleation and growth of crystals modify the system rheological properties that, when measured during the process, make possible the determination of processing rates in function of operational conditions. Viscosity is important in the work of crystallizers because of its influence in heattransfer rates. Knowledge of viscosity allows sizing of pumps, pipes and also calculation of the necessary torque for crystallizers in order to prevent super sizing of equipment. Fluid viscosity is also fundamental in the characterization of flow as well as in modeling mass and heat transfer processes involved in several unit operations used in food industry.