This paper presents an analytic model for a mixing shaft with a standard 45° pitched-blade impeller (PBI) in a baffled mixing vessel. The vibrations and orbits are influenced by a combination of structural and hydrodynamic forces which are sensitive to geometric parameters, fluid properties and rotational speed. Results are included for three water-glycerol mixtures with viscosities of 50 cP, 100 cP and 500 cP and rotational speeds up to 1.3 time the natural frequency of the shaft with both tensile and compressive axial thrust loads resulting from the pitched blades. Experimental results for the expected mean squared vibration response, power spectral densities (PSD) and orbit statistics are presented. A model is presented that explains a number of trends that were experimental observed including asymmetry of the shaft’s vibration amplitude with rotation direction.

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