The silica sand-water two-phase suspension in an unbaffled stirred tank agitated by a standard Rushton turbine was experimentally studied using the PC-6D particle concentration measuring instrument.The critical suspension speeds under different impeller off-bottom clearance and impeller-to-tank diameter ratios were measured and compared with those in the baffled stirred tank.The solids concentration and power profiles under different operating conditions were analyzed.Results showed that the critical suspension speed and power number for the unbaffled stirred tank are smaller than those in the baffled stirred tank.Both of them were found to increase with increase of the off-bottom clearance and decrease with increase of the impeller size at constant tank diameter.For the unbaffled suspension operation, the suspension is the best with impeller off-bottom clearance C=T/5、and impeller-to-tank diameter ratio D=T/3.There is no help to improve the suspension uniformity by increasing the impeller-to-tank diameter ratio or the impeller rotational speed.
