Discussion Forum

Dears COMSOL 4.0a users,

I need to couple two convection and diffusion equation that depend on time. In one of the Convection & Diffusion equation the dependent variable is "S" and in the other Convection & Diffusion equation the time dependent variable is "X". To carry on this I use the "Transport of diluted species" twice (one for "S" and the other one for "X"). On the x-axis I have the reactor's height (H), on the y-axis I have the concentration (S or X). In the equation I have:

*Convection and diffusion (x-velocity and Dispersion coefficient)
*Initial value
*Inflow
*Reaction
*Flux at the reactor entrance: So I "check" Inward Flux for species S or X, and I set up the Flux value. But at the end of the reactors I have a convective flux (reactor is open), how can I set convective Flux in COMSOL 4.0a??? In COMSOL 3.5 there is the option of convective flux but in 4.0a or 4.1 the convective flux does not appears. I assume that if I put a second Flux (Flux 2) and I introduce the reactor's end in the Boundaries but this time I do not "check" the "INWARD FLUX" section, this means that I have a CONVECTIVE FLUX at the end of the reactor??? Is this correct ???

I have a problem with the response, the initial value for S is 10kg/m3 and for X is 12 Kg/m3, at time zero this initial value should be constant, but the COMSOL response tell me that the initial value for S when time = 0 go down (and it should be constant), and the initial value for X when t=0 remains constant (this is O.K.). What could be wrong with my model??

Thanks a lot in advance....