Our final model entailed a much more mathematically
rigorous look at our microreactor. We used a computational fluid
dynamics program, FIDAP, to solve the equations of change for a
characteristic microreactor. This model therefore included the
interrelated effects of momentum, heat, and mass transport.
FIDAP uses the finite element method to converge on a numerical
solution. In order to make the problem more tractable, we limited
it to two dimensions and reaction 1 only.
As can be seen by the resulting graph of the streamlines, the flow is
laminar.
This shows that transport effects in microreactors are different from those in traditional plug flow reactors. In traditional reactors, the flow is turbulent, and it can be safely assumed that the fluid is fairly well mixed everywhere outside a thin boundary layer next to the surface. This assumption can not be made in the laminar regime. Thus mass and heat transfer throughout the fluid are less effective. For example, the graph of concentration in the y-direction shows that there is a gradual concentration gradient across the width of the reactor. This is because reactants must rely entirely on diffusion to transport them to the catalytic surface, whereas in a plug flow reactor turbulent mixing would provide most of the transport outside the boundary layer. Another consequence of laminar flow is that because of the parabolic velocity profile, the fluid in the center of the channel spends less time in the reactor than the fluid nearer the walls, leading to a residence time distribution that affects the reaction rate.
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