Shaft Power Consumption of Stirred Tank with Particles: From the Perspective of Pseudoshearing Thinning Rheological Property of Particles

Abstract

Accurately determining the shaft power consumption is important in the design and scale-up of stirred tanks with particles. Firstly, the apparent viscosity of the stirring particles is proposed. The effects of impeller type, agitation speed, and particle filling level on the apparent viscosity of the stirring particles are experimentally studied with various particles. It was found that larger particles, a greater friction coefficient between particles, and a higher particle filling level all result in a larger apparent viscosity of the particles. The stirred particles show shear thinning behavior, which is similar to the pseudoplastic non-Newtonian fluids. Finally, based on the force analysis and the concept of particles having an apparent viscosity, a model predicting the shaft power consumption in stirring noncohesive particles is proposed. The predicted shaft power in the stirred tank is within ±15% with particles of different sizes. When the model is applied to the 10-times scaled-up stirred tank with geometric similarity, the prediction results of the shaft power are within ±6%.

Experimental investigation of heat generation during the mixing of granular materials in an overhead stirrer

“…The temperature rise corresponds to the generated heat, which is related to the amount of power consumed and subsequently dissipated by the granular medium during agitation. Others also showed such observations [7,8,40], confirming that the torque exerted by the blades to the granular medium increases with blade size, fill ratio, rotating speed and particle size.…”

“…When particles are filled above the blade span, the pressure distribution within the granular medium becomes approximately hydrostatic [40]. Therefore, at higher fill ratios, greater pressure is acting on the particles from those above the blade, leading to a greater resistance for the blade to overcome.…”

Experimental investigation of heat generation during the mixing of granular materials using an overhead stirrer

“…The temperature rise corresponds to the generated heat, related to the amount of power consumed and dissipated by the granular medium during agitation. Others also showed such observations, 7,8,40 confirming that the torque exerted by the blades to the granular medium increases with blade size, fill ratio, rotating speed and particle size. However, further investigation is required to understand better the heat generation behavior of granular materials, particularly in quantifying the generated heat and other forms of energy.…”

“…When particles are filled above the blade span, the pressure distribution within the granular medium becomes approximately hydrostatic. 40 Therefore, at higher fill ratios, greater pressure is acting on the particles from those above the blade, leading to a greater resistance for the blade to overcome. This was also confirmed by Boonkanokwong et al, 8 who showed that the impeller torque was greater for higher fill ratios.…”

“…Similarly, Gijón‐Arreortúa 39 established a relationship between power consumption and a dimensionless number consisting of powder physical properties, operating conditions, and blade configurations for mixing in a helical double‐ribbon impeller. Recently, Bao 40 used the concept of apparent viscosity of granular medium and proposed a model for estimating the shaft power consumption under various agitation speeds, blade types and fill ratios.…”