Abstract
This paper presents the results of an experimental investigation of the power input of pitched blade impellers and standard Rushton turbine impellers in a cylindrical vessel provided with four radial baffles at its wall under a turbulent regime of flow of an agitated liquid. The influence of the geometry of the pitched blade impellers (pitch angle, number of blades) and the off-bottom impeller clearance of both high-speed impellers tested on the impeller power input is determined in two sizes of the cylindrical vessel (0.3 m and 0.8 m diameter of vessel). A strain gauge torquemeter is used in the small vessel and a phase shift mechanical torquemeter is used in the large vessel. All results of the experiments correspond to the condition that the Reynolds number modified for the impeller exceeds ten thousand. The results of this study show that the significant influence of the separating disk thickness of the turbine impeller corresponds fairly well to the empirical equations presented in the literature. Both the influence of the number of impeller blades and the blade pitch angle of the pitched blade impeller were expressed quantitatively by means of the power dependence of the recently published correlations: the higher the pitch angle and the number of blades, the higher the values of the impeller power input. Finally, it follows from results of this study that the impeller off-bottom clearance has a weak influence on the power input of the Rushton turbine impeller, but with decreasing impeller off-bottom clearance the power input of the pitched blade impeller increases significantly.
Highlights
High-speed rotary impellers are generally used for mixing low-viscosity liquids and dispersions under a turbulent regime of flow of an agitated batch [1, 2, 3]
The power input of the standard Rushton turbine impeller (SRTI) and pitched blade impellers (PBI) has in many cases of impellers been studied experimentally, and the results of the experiments have been published in dimensionless form by means of similarity criteria [2] a [3]: l
Power Input Measured at h/T = 0.33 6.51 h/T = 0.5 6.32 h/T = 0.2 h/T = 0.35 h/T = 0.5
Summary
High-speed rotary impellers are generally used for mixing low-viscosity liquids and dispersions under a turbulent regime of flow of an agitated batch [1, 2, 3]. Their main advantage is that they can reduce investment costs for complex gear boxes because their high speed involves transferring the power input from the driving motor to the impeller predominantly via frequency of revolution at a moderate level of torque. The main types of high-speed rotary impellers suitable both for blending pure liquids and for mixing solid-liquid suspensions, gas-liquid dispersions and liquid-liquid emulsions are the standard Rushton turbine impeller (Fig. 1) and the pitched blade impeller The power input of the standard Rushton turbine impeller (SRTI) and pitched blade impellers (PBI) has in many cases of impellers been studied experimentally, and the results of the experiments have been published in dimensionless form by means of similarity criteria [2] a [3]: l 60° D
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