(506a) Impeller Design for Simultaneous Improvement of Economics and Efficiency

Most of the cost of an agitator is in the wetted parts [shaft and impeller(s) within the fluid]. Over the last several years most alloy materials used in mixing processes have increased significantly in price and some by a factor of 2 or more. A comparison of these prices for 6 commonly used alloys will be provided. To minimize cost therefore, much of the impeller design processes will deal with reducing shaft and impeller weight. Most high efficiency impellers used today tend to be much heavier than their lesser efficient counterparts such as the standard 45° pitched blade impeller. However, designing for both reduced cost and high efficiency do not have to be incompatible objectives. Compatible factors that both maintain or improve efficiency and reduce cost will be discussed. Comparisons between an economical high efficiency impeller and an old style high efficiency impeller, designed for efficiency only, will be made. Comparisons will include both process and mechanical parameters and their effects. Reduced impeller weight can also reduce the amount of alloy required for the shafting in critical speed controlled applications. Examples of critical speed controlled designs will be provided for both style impellers.