Baffle-type Tubular Oscillatory Flow Reactor Flow Field Asymmetric Numerical Studies,

The oscillatory flow in a baffled tube reactor provides a significant enhancement of radialtransfer of momentum, heat and mass and a good control of axial back mixing at a widerange of net flow rate. But little has been known about reliable details of thethree-dimensional structure of flow field in this kind of flow because most published studiesin the area were based on the two-dimensional simulation techniques. This paperimplemented a three-dimensional numerical simulation study on the asymmetry of flowpattern in the baffled tube reactor which was observed experimentally. A systematic study bynumerical simulation was carried out which covered a range of oscillatory Reynolds number(Re0) from 100 to 5,000 and employed models respectively for laminar and turbulent flows.It was found in the simulation that under symmetric boundary conditions the transition fromaxially symmetric flow to asymmetric one depended on the numerical technique employed insimulation. With a structured grid frame the transition occurred at Re0 much greater than thatwith an unstructured grid frame, for both laminar and turbulent flows. It is not rational thatthe onset of the transition changes with the accuracy of numerical technique. Based on thesimulation results, it was postulated that the asymmetry appeared in simulations withsymmetric boundary conditions might result from the accumulation of calculation errors butthe asymmetry observed in experiments might result from the slight asymmetry of geometrywhich exists inevitably in any experiment apparatus. To explore the influence of the slightasymmetry of geometry, the effect of the eccentricity of baffles and the declination ofoscillating boundary were studied by use of the finite volume method with a structured gridand adaptive time steps. The simulation result showed that both the eccentricity of bafflesand the declination of oscillating boundary have obvious influence on the asymmetry of flowpatterns for laminar and turbulent flow. More details were discussed in the paper.