Suspension of agitated high concentration slurry within transitional regime

Off-bottom suspension of concentrated slurry was investigated in a mechanically agitated vessel equipped with radial and axial flow impellers in the transitional regime corresponding to NRe from 4500 to 5500 for liquid viscosity from 0.001 to 0.025 Pa.s. Water and glycerol were used as the liquid phases and spherical glass particles were used as the solid phase. Solid concentration was varied from 5 to 45 % v/v. The power measurements in this study is expressed on the basis of total mass of solids suspended due to the consideration that the rate of dissolution and reaction depend to a large extent on the total surface area or amount of solids once complete suspension is achieved. When defined in this form, specific power input is found to decrease with increase in solids concentration, reach a minimum value and increase thereafter. This result is observed in water as well as in glycerol solutions used in this study. Experimental results show that an increase in viscosity leads to an increase in specific power irrespective of the impeller type and solids concentration used. It also appears that the effect of viscosity was found to be significant for the radial flow impeller. In addition, it was observed that the optimum solids concentration at which the specific power is a minimum is not affected by the viscosity but the specific power at this concentration for a given impeller increases with an increase in viscosity.