Chemical and Process Engineering

Abstract

In-line rotor-stators are widely used for power intensive industrial applications, such as deagglomeration, emulsification. There is limited information on characteristic power numbers for different designs which can be used to calculate the average power input as a means to evaluate process performance. This study made use of 18 different rotor-stators, 17 of which were toothed designs with different geometry, and also a commercially available design, with the objectives of evaluating the applicability of different expressions for characteristic power numbers and establishing the effects of geometric variations on the power input.The expression 𝑃 = 𝑃𝑜 1 𝜌𝑁 3 𝐷 5 + 𝑃𝑜 2 𝜌𝑁 2 𝐷 2 𝑄 is found to account for the experimental data over a wide range of operating conditions.Rotor diameter was found to have the most prominent effect on the power input: an increase in rotor diameter from 119.6 to 123.34 mm resulted in an increase in the average power draw. The effect of rotor diameter examined with geometrically similar set ups reducing the diameter from 123.34 to 61.44 mm, for which the mixing chamber was also proportionately smaller, showed a decrease in the power input at a given speed and flowrate as well. The effects relating to the percentage of open area of the stator and number of rotor teeth were less obvious. Increasing the open area resulted in an increase in the power input -an effect which could be observed more clearly as the flowrate (1 to 4 l/s) and rotor speed (at 2000 and 3000 rpm) were also increased. Increasing the number of stator teeth increased the power input and this effect was more prominent when operating at the highest rotor speed of 3000 rpm and at low flowrates (1-2 l/s).