STEADY AND UNSTEADY COMPUTATION OF IMPELLER-STIRRED REACTORS

A general computational approach is presented for numerical modeling o f viscous flow in baffled, impeller-stirred-tank reactors. A multibloc k, body-fitted grid structure facilitates modeling of various impeller and baffle designs, and a new procedure offers averaged velocity data from a complex 3-D CFD dataset. Impellers are modeled precisely, elim inating the need for inputting experimental velocity data for boundary conditions. The method can be used quickly to obtain extremely detail ed flow computations at a fraction of the cost of computing unsteady m oving grid solutions. A steady-state computational approach that negle cts the relative motion between impeller and baffles yields numerical results comparably accurate to full unsteady computations for laminar flow at a fraction of the time and expense. The approximate steady-sta te method is used to predict power requirements of a Rushton turbine i n laminar flow. An unsteady, moving grid technique provides time-accur ate solutions for the pow inside an impeller-stirred reactor with side -wall baffles. These computed results are compared with those using th e approximate steady-state method and with experimental measurements. The unsteady, moving gild method uses two different initial conditions : one starting from rest and the other starting from an approximate st eady-state solution obtained at the starting position of the impeller relative to rite baffles. For unsteady simulations of laminar flow in stirred vessels, the final operating condition call be achieved much m ore efficiently if the solution obtained from the steady-state procedu re is used as an approximate initial condition.