Figure 7. Methanol conversion 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.
The hydrogen productivity results are presented in Figure 8 for 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. 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. The featureless wall is defined by a microchannel that has a gap not inclusive of the depth of the recessed features and having the same width and length. As the Reynolds number increases the importance of inertial forces increases. For higher inertia or momentum streams, maintaining the momentum in a single primary direction rather than reversing or changing directions makes it easier to keep the stream turning. As the stream keeps turning, it keeps moving more and more flow or molecules into the active surface features where they may interact with the walls that exchange either heat or mass or both. Mass of fluid entering a surface feature is defined as the amount of mass at the inlet to a surface feature section that enters at least one surface feature in a surface feature section, wherein entering a surface feature means the fluid molecule breaks the plane of the recessed surface feature and moves out of the bulk flow channel. Computational fluid dynamics code should be used to evaluate the percentage of mass that enters at least one surface feature in a surface feature section, which allows the evaluation of the fluid flow path lines to be illustrated and traced through the surface feature section. The surface feature section should be discretized with a minimum of six volume cells in the depth and length directions to get reasonable flow discretization, with the main straight channel discretized with proportionally sized cells to maintain the cell size continuity in the channel adjacent to the surface features and the spaces between the surface features. The Reynolds number is the commonly used ratio of the inertial over the viscous forces seen by flow in a channel. Its definition is the ratio of the mass flux rate times the hydraulic diameter divided by the dynamic viscosity. Coatings could also be applied onto microchannel walls by filling channels to the desired height with a liquid coating composition and removing volatile components under reduced pressure. Care may need to be exercised to avoid bubbling defects. The effect of surface features on the reactor performance is explored for the steam reforming reaction. The intent of the features is to increase the conversion per length, especially at low catalyst activity. The surface features increase the available surface area for catalyst, they allow a solution derived catalyst to be wash-coated uniformly, and they reduce external mass transport limitations in the bulk microchannel and thus allow the reactor to operate closer to the intrinsic potential of the catalyst activity.