Figure 8. Hydrogen productivity of the reactor wherein the volume occupied by the catalyst supported on a mesoporous matrix plus the volume of bulk flow path that is adjacent to the catalyst supported on a mesoporous matrix defines the volume of reaction chamber.
4. Conclusions
The effect of surface features on the reactor performance is explored for the steam reforming reaction. The conversion rate is used to compare the reactor performance of different configurations. For the purpose of comparison, a baseline case is modeled which is a straight channel of the same dimensions as those for the cases with surface features in terms of channel length, channel width, and gap size. The reactor performance with surface features is quantitatively measured using different enhancement factors. The major conclusions are summarized as follows:
The surface features are preferably at oblique angles, neither parallel nor perpendicular to the direction of net flow past a surface.
Flow boiling can achieve very high convective heat transfer coefficients, and that coupled with the isothermal fluid allows the heat transfer wall to remain at quasi-constant temperature along the flow direction.
Due to the existence of vapor slugs, severe flow and pressure oscillation may occur in microchannel boiling.
Critical heat flux occurs when the temperature difference reaches a point where the heat transfer rate changes from nucleate and bubbly flow to local dry out and gas phase resistance starts to dominate heat transfer.
As the momentum is increased at higher Reynolds numbers, the relative vorticity or angular force to spin the fluid also increases and thus the number of contacts or collisions with or near the active surface feature walls is also increased.
The performance enhancement of the active surface features relative to a corresponding featureless or flat or smooth wall is typically improved as the residence time is decreased.
 
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