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

An approximate steady-state method is devised for computing the flow field in a baffled impeller-stirred tank reactor. The flow field in a cylindrical tank with a 45 degrees pitched-blade impeller rotating at 100 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 steady-state analysis involves accurately defining the geometry of the miring tank using a multiblock grid technique. The flow is solved from a rotating frame of reference for a single position of the impeller relative 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 averaged numerical predictions obtained using this approximate steady-state method for the radial and axial velocity components agree well with the LDV data. The predicted magnitude of the tangential velocity component, however, is higher than the experimentally measured values. Closer agreement of the tangential velocities with experimental values is obtained 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 mixing vessels to obtain flow-field results for baffled vessels much more efficiently than using full unsteady Navier-Stokes simulations.