Browsing by Author "Sparks, T."
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Item Open Access Fluid mixing in rotor/stator mixers(Cranfield University, 1996-12) Sparks, T.; Brown, D. E.An industrial rotor-stator mixer was fitted into a flow loop to carry out overall power balance, flow visualisation and residence time distribution experiments. These were performed on various rotor-stator geometries and a half-scale unit. The overall power measurements showed that a large amount of power was given to the fluid by the rotor and estimates of the local turbulent energy dissipation rate per unit mass, e, were made using these data. It was found that the pumping efficiency of rotor- stator mixers is - 10 to 20% and an expression for the motor power (when the flow rate is controlled) was found. The flow pattern was characterised by a high tangential velocity in the rotor followed by an abrupt transformation to radial flow through the stator. It was suggested that the kinetic energy of the fluid in the rotor is transformed to pumping, ftiction and turbulence in the stator and that this is the region of greatest importance for mixing. The residence time distribution is characterised by a region of plug flow in series with a region of mixed flow. The flow through the volute has a dominant effect on the overall residence time distribution and the RTD is insensitive to operating condition (flow rate, rotor speed) or geometry. The knowledge gained from the above experiments was used to design diazo-coupling experiments (a mixing-sensitive competitive chemical reaction with well known kinetics) such that they gave qualitative information (e. g. best feed position) and quantitative information (e. g. turbulent energy dissipation rate) on the performance of a rotor-stator mixer. e was found to be proportional to the power given the fluid by the rotor and estimates for e of order 500 W kg-' were made using a micro-mixing model.Item Open Access Operational characteristics of rotor/stator mixers(Cranfield University, 1993-08) Sparks, T.; Brown, D. E.Fast chemical reactors require rapid mixing, and literature shows that rotor/stator mixers can provide this. Results have been published, at small scale, showing rotor/stator mixers to be promising as chemical reactors. An industrial size rotor/stator mixer has been procured and fitted into a test loop. Instrumentation was used to measure shaft torque, shaft speed, differential pressure and differential temperature. Measurements were used to produce an energy balance for the mixer that could be used to assess its mixing performance, based upon general descriptions of mixing. Residence time distribution (RTD) curves were obtained and it was shown that the mixer exhibited substantial backmixing. Modifications to the mixer are proposed that may produce a RTD that better approximates plug flow. It is concluded that if the mixer could be made to better approach plug flow, as mixing rates would be very high, use of such a device could improve the product quality from a competitive chemical reaction.