Enhanced Performance With an Impinging Jet Flow Configuration for PEMFC

A flow structure which delivers the reactant transversely to the MEA using an impinging jet configuration at cathode side is proposed and modeled to examine its effectiveness for enhanced PEMFC performance, especially at high current densities. A two dimensional, non-isothermal, multi-phase model was developed to predict the performance of an impinging jet. The computational model was validated with published experimental data for a conventional PEMFC. For enhanced performance, a macro-porous gas diffusion layer with permeability in the order of 1e−09 m2 is required for the impinging jet design to be effective. Compared to standard channel flow, a single impinging jet design can improve fuel cell performance up to 80% at high current densities. A multiple impinging jet design is further suggested as an effective way to achieve flow and species uniformity with results in more uniform catalyst utilization. Compared to a single impinging jet, a multiple jet gives up to 14% predicted enhancement at a high current density at about 2A/cm2. Experimental validation is needed for the proposed impinging jet configurations.

Catalyzed Big-Bang nucleosynthesis

We point out that the existence of metastable, τ >103 s, negatively charged electroweak-scale particles (X–) alters the predictions for lithium and other primordial elemental abundances for A > 4 via the formation of bound states with nuclei during Big-Bang nucleosynthesis (BBN). In particular, we show that the bound states of X– with helium, formed at temperatures of about T = 108 K, lead to the catalytic enhancement of 6Li production, which is eight orders of magnitude more efficient than the standard channel. In particle physics models, where subsequent decay of X– does not lead to large nonthermal BBN effects, this directly translates to the level of sensitivity to the number density of long-lived X– particles (τ > 105 s) relative to entropy of nX – / s [Formula: see text] 3 × 10–17, which is one of the most stringent probes of electroweak scale remnants known to date. It is also argued that unstable charged particles with lifetime of order ~2000 s may naturally lead to the depletion of 7Li by a factor of two, making it consistent with observationally determined abundances. PACS No.: 98.80.Ft