Experimental Study On Power Consumption Of Wet Particle Systems In A Stirred Mixer

Stirring of particle-water system is an important unit operation in many fields,such as chemical,food,catalysis and pharmaceutical,and stirred tank mixers are widely used in these industries.The stirring shaft power consumption of particle-water systems in stirred mixers is important parameter in design of mixer.The establishment of shaft power consumption prediction model is an important method to study the stirring shaft power consumption in particle-water systems.This method can be used for the design and scale-up of stirred mixers in industrial applications.In this study,glass beads with an average particle size from 1 to 5 mm were used as experimental materials,and three different types of impellers,i.e.,flat blade impeller,frame impeller and double helical ribbon,were used,in a flat-bottom cylindrical stirred mixer with an inner diameter of 210 mm.The effects of material characteristics and stirring parameters on the power consumption characteristics of particle-water systems were studying by using the control variable method.Considering the effects of each variable on power consumption,a shaft power consumption prediction model was establishment.Based on the concept of fluid viscosity,the apparent viscosity of particle-water systems,a parameter characterizing the viscosity of particle-water systems,is proposed to study the flow behavior and rheological properties of particle-water systems in stirred mixers.The results show that with the increase of the free liquid volume ratio,the power consumption of particle-water systems increases first and then decreases to lower than that in stirring dry particle systems,and reaches the maximum power consumption when the free liquid volume ratio is 0.2008.With the increase of the relative material filling height,both the power consumption and the unit mass power consumption increase.The recirculation zone appears in the dry particle system stirred by flat blade impeller,and gradually disappears with the increase of the material filling relative height.When the dry particle systems is stirred,the power consumption increases with the increase of the average particle size;however,when the particle-water system is stirred,the power consumption decreases with the increase of particle size for glass beads with particle size of 1 mm,2 mm and 3mm.Adding a small amount of water to particles,the porosity of the particle bed of 1 mm glass beads will increase.With the increase of agitation speed,the stirring power consumption of particle-water systems increases under different free liquid volume ratios,and the increase rate becomes faster in the form of concave function.The power consumption prediction models of particle-water system were established by dimensional analysis and model analysis,respectively,with the relative errors of prediction within 25%,and10%,respectively.In laminar stirring,the apparent viscosity of particle-water system decreases with the increase of rotation speed,which is similar to the yield pseudoplastic fluid.The yield stress increases first and then decreases with the increase of free liquid volume ratio,which is the same as the influence of water content on power consumption.