LDA Measurement in the Impeller Region of Stirred Vessels: An Assessment of Measurement Technique

J. Stelmach and E. Rzyski

Abstract
Results of measurements of liquid tangential velocity in the region of a self-aspirating disk impeller taken by a laser anemometer through the side wall and bottom of the tank are compared in the paper. It appeared that the measurement method had the most significant influence on the mean velocity. The effect on other values, such as mean velocity pulsations or energy dissipation rate, is smaller or even negligible. In the impeller region a strong dependence of instantaneous velocities on the blade position in relation to the measurement point (angular velocity distribution) was observed. A periodic velocity component can be approximated by a sinusoidal relation and eliminated. It is also possible to average velocities and velocity pulsations by intervals. This enables the extrapolation of velocity in the “dead” measurement zone.

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Keywords
Agitated tank, LDA measurements, Mixing, self-aspirating disk impeller, tangential velocity of liquid