Davide Louis Simone

Fuel selection for a regenerative organic fuel cell/flow battery: thermodynamic considerations

Our work focuses on the feasibility of utilizing organic fuels for virtual hydrogen flow cell battery systems, based on thermodynamic considerations of fuel hydrogenation/dehydrogenation reactions. An assessment of the energy density and open circuit potentials (OCPs) as determined by the structure of carbocyclic and heterocyclic saturated hydrocarbons and their dehydrogenation products has been pursued and we identified promising organic carriers that could yield theoretical OCPs higher than that for the hydrogen fuel cell.

Accounting for conducting inclusion permeability in the microwave regime in a modified generalized effective medium theory

We standardize the approach to predict composite permeability, μeff, to determine the reflection (R), transmission (T), and absorption (A) using the generalized effective medium theory. For stainless steel (SS) spheres and fibers, we calculate the inclusion permeability based on the effective susceptibility generated by eddy currents in a time-varying magnetic field. This gives reasonable agreement with measured μeff when used in the Bruggeman theory and agreement with R, T, and A within 10%. For SS flakes, we fit the imaginary component of μeff to a single-peak Lorentzian for each loading and use typical fitting parameters to predict μeff and, ultimately, R, T, and A within 5%. The fitting exponent t was constant for all frequencies for a given inclusion shape (4.7, 1.6, and 1.7 for spheres, fibers, and flakes, respectively) and Ax typically varied with inverse volume loading rather than percolation threshold. Interestingly, at percolation for the fibers, Ax approached a constant that approximately equaled the observed percolation threshold.

Predicting effective permittivity of composites containing conductive inclusions at microwave frequencies

We predict the effective dielectric properties at microwave frequencies of composites containing various volume loadings of high conductivity (stainless steel or iron) spheres or flakes by adapting the semi-empirical method developed by McLachlan. Rather than the typical approach of fixing A (A = 1/vc – 1, where vc is percolation threshold) for a given inclusion shape, we consider it as an unknown and fix one of the geometric exponents. We observe that A varies linearly with the inverse of volume loading with a higher slope for flakes than spheres. The exponent is consistently higher for spheres than flakes and for iron than stainless steel. We achieve good agreement between measured and calculated permittivity over a wide range of volume loadings, inclusion shapes, and materials from 3 to 20 GHz.

A semi-empirical approach for predicting the performance of multiphase composites at microwave frequencies

We predict the fraction of incoming electromagnetic signals reflected (R), transmitted (T), and absorbed (A) by multiphase composites containing combinations of stainless steel spheres and flakes at microwave frequencies by adapting a semi-empirical method. Using single inclusion fitting exponents, we fit expressions for R, T, and A for each loading combination to determine the parameter Ax and the hosts fitting exponent. The host exponent is constant for all composites while Ax varies linearly with the inverse of total inclusion volume loading (vtot) for a given flake loading (vf). The insensitivity of Ax to Vf at a given vtot indicates that the volume loading of spheres, which is generally higher than that of the flakes in the studied composites, drives effective behavior.