STEADY-STATE MODELING AND EXPERIMENTAL-MEASUREMENT OF A BAFFLED IMPELLER STIRRED-TANK

An approximate steady-state method is devised for computing the flow f ield in a baffled impeller-stirred tank reactor. The flow field in a c ylindrical tank with a 45 degrees pitched-blade impeller rotating at 1 00 rpm and four stationary rectangular side-wall baffles is simulated using a new approximate steady-state approach. The method provides an alternative to a full unsteady Navier- Stokes simulation. The new stea dy-state analysis involves accurately defining the geometry of the mir ing tank using a multiblock grid technique. The flow is solved from a rotating frame of reference for a single position of the impeller rela tive to the side-wall baffles. The steady-state numerical results are then spatially averaged and compared with time-averaged data obtained experimentally using laser Doppler velocimetry (LDV). Spatially averag ed numerical predictions obtained using this approximate steady-state method for the radial and axial velocity components agree well with th e LDV data. The predicted magnitude of the tangential velocity compone nt, however, is higher than the experimentally measured values. Closer agreement of the tangential velocities with experimental values is ob tained using a finer grid and it is found that a relatively fine grid is needed for accurately predicting the tangential velocity magnitude. Use of this approximate steady-state method allows designers of mixin g vessels to obtain flow-field results for baffled vessels much more e fficiently than using full unsteady Navier-Stokes simulations.