Discussion Forum

Hello,

I am trying to build up a model to simulate single phase gas flow in a fluidized bed reactor. I am using k-w turbulence and wall functions for the wall boundaries and pressure condition for the outlet.. I have problem with implementing my inlet conditions. When I implement the gas flow in terms of velocity at the inlet boundary, the convergence is relatively faster and the solution can be obtained. But when I implement a coinciding mass flow at the inlet boundary, the convergence is hard and I obtain a weird flow profile ( as in reversed gas flow at inlet etc...).

I use a perforated air distributor plate at the inlet of my reactor so my velocity profile at that boundary is not a flat/uniform profile. From the documentation of my reactor, I know that 80-90% of the volumetric air flow is directed at the center while the rest 10-20% of the flow passing through the sides. I introduce initial velocities from the calculation of the surface areas of pores and the respective fraction of total surface area from mass flow calculations but the resulting flow field I obtain is 1) high in magnitude 2) I obtain a field with some back mixing around wall regions ( which is not reported in literature). When I try to implement a mass flow rate inlet condition in terms of a velocity profile function that I formed in terms of rectangle functions, the model can not converge. I believe the problem is that I want to express mass flow rate, a scalar quantity, in terms of the double integral of the velocity, a vector quantity. I tried increasing the relative tolerance, iteration number, and changing solver to highly nonlinear but I could not obtain a solution. Anyone happens to know the reason for the convergence issue?