LIQUID MIXING

Food liquid mixtures could in theory be sampled and analysed in the same way as solid mixtures but little investigational work has been published on this, or on the mixing performance of fluid mixers. Most of the information that is available concerns the power requirements for the most commonly used liquid mixer - some form of paddle or propeller stirrer. In these mixers, the fluids to be mixed are placed in containers and the stirrer is rotated. Measurements have been made in terms of dimensionless ratios involving all of the physical factors that influence power consumption. The results have been correlated in an equation of the form
(Po) = K(Re)n(Fr)m (12.7)
where (Re) = (D2Nr/m), (Po) = (P/D5N3r) and this is called the Power number (relating drag forces to inertial forces), (Fr) = (DN2/g) and this is called the Froude number (relating inertial forces to those of gravity); D is the diameter of the propeller, N is the rotational frequency of the propeller (rev/sec), r is the density of the liquid, m is the viscosity of the liquid and P is the power consumed by the propeller.



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