Mary Elizabeth Heigel
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Impeller power draw in liquid-only systems is well understood; however, this is not the case for liquid-solid suspensions. Typically liquid-only behavior is extrapolated, with the assumption that power draw is proportional to suspension density. Recent work has indicated that power draw can be affected by the presence of solids that do not alter the suspension density. This effect appears to be a function of particle size, and while past work has assumed that all impeller types are affected by solids in the same manner, this has never been verified experimentally. The subject literature is perplexing due to most studies considering only a single impeller type at a very limited number of operating conditions. In this study, the power draw was characterized in liquid-solid suspensions for a number of impeller types including axial-flow, mixed-flow, and radial-flow (with and without a disc). To develop a deeper understanding of the effect of solids on impeller power draw, the following testing was performed. To eliminate the effect of suspension density on power draw, neutrally buoyant solid particles were used. This was done by using salt water that matched the particle density as the liquid phase. Two particle sizes were studied to consider the effect of this parameter. It was found that the power draw increased slightly for both particle sizes as an increased amount of solid was added. Testing was also performed in which addition of solids changed suspension density. Again two solids were used: fine acrylic solids with a density less than twenty percent higher than the liquid and granular sand with a density two and a half times that of the liquid. This testing indicated that the increase of specific gravity increased the relative power draw linearly for each different impeller. For all the tests the various impellers behaved differently.
Independent Research - Undergraduate
Kevin J. Myers
Primary Advisor's Department
Chemical and Materials Engineering
Stander Symposium project
"Impeller Power Draw in Liquid-Solid Suspensions" (2017). Stander Symposium Projects. 983.