Figure 3. Hydrogen mole fraction contour map in the reactor wherein the leading edge of the subsurface layer has a tapered shape that corresponds to the angle of cross-bars in the top-most layer so that fluids from the bulk flow path are not trapped beneath the top-most layer.
The temperature contour map in the reactor is plotted in Figure 4 wherein the leading edge of the subsurface layer has a tapered shape that corresponds to the angle of cross-bars in the top-most layer so that fluids from the bulk flow path are not trapped beneath the top-most layer. For decades, steam reforming has been the principal industrial process for making hydrogen. More recently, steam reforming has attracted great interest as a possible means to supply hydrogen for fuel cells [57, 58]. There have been intensive research efforts over many years to improve the steam reforming process [59, 60]. Despite these efforts, problems continue to exist with catalyst performance and cost, and the need for catalyst replacement or regeneration due to the rather harsh conditions in which steam reforming is typically conducted. The volume of a connecting channel or manifold is based on open space. The volume includes depressions of surface features. The volume of gate or grate features, which help equalize flow distribution as described in the incorporated published patent application, are included in the volume of manifold; this is an exception to the rule that the dividing line between the manifold and the connecting channels is marked by a significant change in direction. Channel walls are not included in the volume calculation. Similarly, the volume of orifices, which is typically negligible, and flow straighteners are included in the volume of manifold. Boiling is known as a highly efficient heat transfer mechanism that provides high heat flux density based on surface area and volume. There are several different boiling regimes including low vapor quality flow, nucleate boiling, film boiling and transition boiling. Nucleate boiling is mostly found in the industrial applications. Boiling can take place at heat transfer surface both in fluid flow and fluid pool or in the volume of the fluid. Through phase change of the fluid, flow boiling has the potential to achieve an isothermal heat sink in the fluid while the phase change is occurring. 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. This is a desirable heat transfer situation for many thermal, nuclear and chemical process applications. In many chemical processes, such as an exothermic chemical reactor, the reaction rate strongly depends on the local temperature. An optimal temperature throughout the reaction zone often leads to a maximum yield, conversion and desired selectivity. Thus, boiling heat transfer is used in process control or thermal management of various reactions to maintain an isothermal thermal condition where the exothermic reactions releases heat. Compared to a boiling process control, a cooling system via single-phase fluid convection generally cannot achieve a near isothermal boundary condition for the reactions without large flow rates needed to keep the stream at constant temperatures and increase the convective heat flux.