Power characteristics of unsteadily forward–reverse rotating impellers in an unbaffled aerated agitated vessel

Abstract

Power characteristics of an unbaf¯ed aerated agitated vessel with unsteadily forwardreverse rotating impellers, ie a new type of gas±liquid agitator named`AJITER', treating viscous Newtonian liquids were studied experimentally. Measurements were ®rst made on the agitation torque, ie the torque on the drive shaft on which forward±reverse rotating impellers with four deltatype blades were attached, and the data obtained were analyzed by ®tting them to an equation consisting of two terms with respect to the resistance of the¯uid, one due to viscous drag and the other due to added moment of inertia. The effects of operating conditions and physical properties of liquids on the drag and added moment of inertia coef®cients were then evaluated, and empirical relationships which estimate values of these coef®cients, useful to predict the unsteady behavior and magnitude of agitation torque, were presented. Furthermore, equations were developed for estimating the average and maximum power consumptions as a function of the drag and added moment of inertia coef®cients. Prediction of respective power levels in AJITER by these equations was also discussed. # 2001 Society of Chemical Industry Keywords: unsteady torque; unbaf¯ed aerated agitated vessel; unsteadily rotating impeller; drag and added moment of inertia coef®cients; average and maximum power consumptions

Unsteady Mixing Characteristics in a Vessel with Forward‐Reverse Rotating Impeller

“…Moreover, it was found that the C d was also independent of the frequency of impeller rotations f. As the drag coefficient was independent of the Reynolds number, it suggested that the Newton law for turbulent flow was valid and turbulent flow was achieved [10,11].…”

“…As distinct from other work, the function of impeller oscillation in time was similar to a triangle wave. In all previous studies [10][11][12][13][14] the impeller rotational speed N was sinusoidally changed in time.…”

“…Forward-reverse agitation could be performed in laminar flow [3,8,9] to minimize the effect of isolated mixing regions or other mixing pathologies. In the turbulent flow regime forward-reverse mixing proceeds more uniformly in the vessel [1,[10][11][12][13][14] but the high shear level of the forward-reverse agitation mode could increase mixing time and mixing power.…”

Liquid Flow in Impeller Swept Regions of Baffled and Unbaffled Vessels With a Turbine-Type Agitator

“…The impeller rotation rate was set to 100 rpm. The impeller power consumption was determined by measuring the torque with strain gauges fitted onto the shaft (Yoshida et al, 2001). Tomographic visualization of the liquid flow was done on the different horizontal planes normal to the impeller shaft, using the particle suspension method.…”

Gas-Liquid Mass Transfer in an Unbaffled Vessel Agitated by Unsteadily Forward-Reverse Rotating Multiple Impellers

“…Additionally, the angular difference of position between the blades of one impeller and those of upper and lower adjacent impellers was 45 degree. In the mechanism for transmitting motion used here (Yoshida et al, 2001), when the crank is rotated one revolution, the shaft on which the impellers were attached first rotates up to one-quarter of a revolution in one direction, stops rotating at that position and rotates onequarter of a revolution in the reverse direction. That is, the angular amplitude of forwardreverse rotation, θ o , is π/4.…”