Lalit M. Pant

Multigrid hierarchical simulated annealing method for reconstructing heterogeneous media.

A reconstruction methodology based on different-phase-neighbor (DPN) pixel swapping and multigrid hierarchical annealing is presented. The method performs reconstructions by starting at a coarse image and successively refining it. The DPN information is used at each refinement stage to freeze interior pixels of preformed structures. This preserves the large-scale structures in refined images and also reduces the number of pixels to be swapped, thereby resulting in a decrease in the necessary computational time to reach a solution. Compared to conventional single-grid simulated annealing, this method was found to reduce the required computation time to achieve a reconstruction by around a factor of 70-90, with the potential of even higher speedups for larger reconstructions. The method is able to perform medium sized (up to 300(3) voxels) three-dimensional reconstructions with multiple correlation functions in 36-47 h.

Mass Transport Measurements in Porous Transport Layers of a PEM Fuel Cell

Porous transport layers are an integral part of polymer electrolyte fuel cells (PEMFC). In order to optimize the catalyst layer performance and reduce catalyst consumption, a thorough understanding of mass transport through porous media is necessary. Currently, there is a lack of experimental measurements of effective mass transport properties of porous transport layers. Further, mass transport theories in the literature, such as the binary friction model by Kerkhof [1], have not been extensively validated for porous media. In the present study, mass transport measurements have been performed on the porous media of a PEMFC, namely a GDL and an MPL. The experimental setup described by Pant et al. [2] has been used. The setup uses the diffusion bridge/counter-diffusion technique for the mass transport measurements. The experimental setup has the advantage that it can be used to perform studies for pure diffusion and convection-diffusion mass transport. The setup also facilitates measurement of permeability of porous media, which can then be used in convection-diffusion studies. Preliminary permeability measurements of GDL and MPL from the setup show good agreement with values available in literature. In preliminary experimentation, the conventional diffusivity correlations like Bruggeman equation have been found to overpredict the diffusivities.Copyright

Design of an Experimental Setup to Study Mass Transport in Micro-Nano Capillaries and Porous Media

Study of gas diffusion is critical in understanding the process of mass transfer in porous media, which is an integral part of polymer electrolyte membrane fuel cells (PEMFCs). An experimental method is presented to study the mass transfer processes in micro-nano capillaries, which is further extended to study the transport in the porous media of fuel cells. A diffusion bridge setup, similar to the one presented by Remick and Geankoplis [1] has been used. The experimental setup facilitates the study of binary and multicomponent mixture transport through micro-nano capillaries and porous media. The setup can perform studies for two cases viz., pure diffusion and convection-diffusion. Using pressure controls in both channels, the pressure gradient across the capillaries is varied to study the convection diffusion process in detail. The results obtained from the study will be used to review various models of mass transport available in literature.Copyright