268445 Modelling of Turbulence in Agitated Vessels Operating At "Just Suspension Speed"

Monday, October 29, 2012: 2:10 PM
Frick (Omni )
Richard K. Grenville1, Minye Liu1 and Alvin W. Nienow2, (1)DuPont Engineering Technology, Wilmington, DE, (2)Birmingham University, Birmingham, UK

Just suspension impeller speed, Njs, is an important design parameter for agitators.  It is the optimum speed when suspending and dissolving particles.

Hydrofoil impellers achieve Njs for half of the power input of a pitched blade turbine of the same diameter (Grenville et al. 2010) but the maximum Turbulent Kinetic Energy Dissipation Rate (TKEDR) generated by a hydrofoil is double that generated by a pitched blade turbine at the same vessel averaged power input per mass (Grenville and Brown 2012).  Operating at Njs, the maximum TKEDR generated by the two impellers will be approximately equal.

In this paper we have calculated Njs for three impellers; a hydrofoil and pitched blade and Rushton turbines.  CFD simulations of the single-phase flow and turbulence quantities have been calculated, at the blades and at the vessel base, in order to explain the difference in the impellers' power requirements when operating at Njs.

Recommendations regarding impeller selection for suspension and mass transfer will be discussed.

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