(40c) Mixing Performance of the Novel Kdm Impeller in Small Laboratory-Scale Systems

Since small (<100 ml) lab-scale systems commonly encounter significant mixing challenges, researchers from the Engineering and Process Sciences Laboratory of The Dow Chemical Co. developed and patented a novel KDM impeller for overhead mixing within such unbaffled systems. This impeller consists of multiple twisted ribbon elements mounted on a rotating shaft. Through laboratory experiments and computational fluid dynamics (CFD) simulations, the performance of the KDM impeller was compared to that of vendor-offered impellers in three different lab-scale mixing systems. In fluid viscosities ranging from 5,000-30,000 cP, the KDM impeller produced the desired mixing in significantly less time than each commercially-offered impeller system.

Experiments and simulations characterized KDM impeller operations and yielded the optimum ratios of KDM diameter-to-vial diameter (D/T), liquid submergence-to-KDM diameter (s/D), and off-bottom clearance-to-KDM diameter (c/D). The optimal speed at which the KDM impeller rotates depends on the fluid system of interest. The design of the KDM impeller was refined for the applications described in this work by optimizing the length-to-diameter ratio (L/D) of the impeller elements, as well as the number of repeated KDM elements so as to meet the recommended values of s/D, c/D, and L/D. Other crucial features of the optimized KDM design included twisting all elements in the same direction (be it clockwise or counter-clockwise), and the 90 degree off-set angle between adjacent elements. The KDM impeller is well suited to laboratory and mini-plant scales, but its high relative mass could make it impractical at some larger scales, depending on fluids of interest, and materials of construction. Identifying the size at which the KDM becomes impractical was beyond the current effort.