Key issues in the microchemical systems-based methanol fuel processor: Energy density, thermal integration, and heat loss mechanisms

CFD analysis of the effects of the flow distribution and heat losses on the steam reforming of methanol in catalytic (Pd/ZnO) microreactors

“…Losses by radiation have been neglected in this study due to the relatively low temperatures involved in the SRM. According to previous studies, radiation can contribute with increased heat losses by about 25% [10,11]. It is not expected that this affects the main conclusions drawn from this work.…”

“…This is equivalent to feed the microreactor block with a feed stream flow rate between approximately 32 and 815 cm 3 / min (STP). Assuming a PEM fuel cell (PEMFC) efficiency of 60% and hydrogen utilization factor of 75% [10], the microchannel reactor coupled to a PEMFC of suitable size would be able to generate up to about 75 W el operating at 50,000 h À1 and almost complete methanol conversion.…”

“…Holladay et al found for a very small microreformer that when producing only 100 mW el the efficiency was as low as 4.5% due to the strong influence of heat losses, that were dominated by thermal conduction [8,9]. Shah and Besser have investigated the heat losses from a planar silicon microreactor for the SRM sized for obtaining 0.65 W el [10,11]. The total energy requirement amounted to 0.13 W for the SRM, 0.20 W for vaporizing the reactants and 1.0 W for compensating the heat losses; that is, up to 75% of the energy consumed was lost to the surroundings.…”

The Future of Energy Storage Systems

“…In the case where no water recycling is employed to minimize system complexity, water has to be carried with methanol for the reforming. With a stoichiometric steam to carbon ratio of 1:1, this reduces the net energy density to 3000 Wh/l (4550 Wh/kg)"' [57]. Unfortunately, unlike Hydrogen PEM, where we can assume that all of the polarization losses are located at the cathode, in DMFC the losses at the anode and cathode are comparable.…”

High vs. low temperature reforming for hydrogen production via microtechnology

“…Microreactor technology (sub-millimeter characteristic length scale) has been investigated over the last years as a "vehicle" to bring the reforming technologies to commercialization for applications ranging from portable systems, in which the reactor size is limited by the application size, to transportation and decentralized stationary systems (Anxionnaz et al, 2008;Holladay et al, 2004b;Mills et al, 2007;Norton et al, 2005;Shah and Besser, 2007;Tonkovich et al, 2005Tonkovich et al, , 2004Vlachos, 2009). Microreactors exhibit much higher heat and mass transport rates than conventional reactors, enabling downscaling of chemical processes.…”