Effect of impeller type and number and liquid level on turbulent blend time

Impellers are the core element of a mixing system. The size and the number of impellers affect the performance of a mixing system. There have been literature studies reporting a correlation among the power number, the blend time and the impeller size of a single impeller mixing system using one general equation. This current research tested numerous axial-flow and radial-flow impellers. This study found that the widely accepted FMP Parameter may not be as accurate as often stated, especially for multiple impeller system or higher liquid level. The impeller type may affect the value of FMP Parameter. Also the correlation between dimensionless blend time and impeller size may need to be developed individually for each impeller type. The FMP correlation indicates that for a fixed blend time and impeller diameter, the impeller power requirement should be the same for all impellers, regardless of type. This research found that this FMP correlation predicts the mixing time reasonably well for most of the impeller types. As for the sawtooth impeller, it has larger experimental power requirement than the prediction. Based on the result above, FMP correlation has its limitation when predicting single impeller blend times. Further, double and triple impeller systems have been studied. Two methods of correlating the data are used for this multiple impeller blending study: (i) A modified FMP correlation among impeller system power number, the liquid level, and the blend time. (ii) Blend time correlation among impeller type, impeller number and liquid level separately for each impeller style based on Fasano and Penney approach (1991). The modified FMP correlation method offers a reasonable way that the blend time of all types of impeller can be predicted via the same correlation while taking liquid level into consideration. The second method that predicts the blend time according to impeller type has a smaller deviation between experimental data and correlation than first method