Analysis of the drying stage in the technology of supported catalysts

The distribution of the precipitated active component has been analyzed using the concepts of moisture transfer mechanism for the evaporation of porous materials. Formulas are proposed for the low-dispersity phase, depending on the precipitation parameter. The calculations performed using a statistical porous environment model are in reasonable agreement with the experimental data.

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Mathematical simulation of anodic intercalation of graphite in dilute nitric acid

The article suggests a mathematical model for the process of anodic intercalation of the dense graphite suspension in dilute nitric acid, where the spontaneous intercalation is absent. The model is based on the idea of electric neutrality of a graphite particle, due to which the anion current NO₃⁻ entering the particle is precisely equal to the quantity of electrons, which are diverted from a particle to a current lead according to the mechanism of electronic conductivity provided by the outer constriction of the suspension. The anodic polarization is conditioned by the mass transfer of anions NO₃⁻ inside the equipotential graphite particle. The computational solution of the problem showed that even at a small suspension layer height (2 cm), there is a significant nonuniformity of intercalation, which corresponds to the data provided in the literature. A method for the estimation of an intercalation nonuniformity and a method for its reduction by using a multistep process were suggested. The results of the computation can be used for an estimation of the technical characteristics of the final product.     

The first-principles treatment of the electron-correlation and spin-orbital effects in uranium mononitride nuclear fuels

The DFT+U calculations were employed in a detailed study of the strong electron correlation effects in a promising nuclear fuel-uranium mononitride (UN). A simple method for solving the multiple minima problem in DFT+U simulations and insure obtaining the correct ground state is suggested and applied. The crucial role of spin-orbit interactions in reproduction of the U atom total magnetic moment is demonstrated. Basic material properties (the lattice constants, the spin- and total magnetic moments on U atoms, the magnetic ordering, and the density of states) were calculated varying the Hubbard U-parameter. By varying the tetragonal unit cell distortion, the meta-stable states have been carefully identified and analyzed. The difference in the magnetic and structural properties obtained for the meta-stable and ground states is discussed. The optimal effective Hubbard parameter U(eff) = 1.85 eV reproduces correctly the UN anti-ferromagnetic ordering, and only slightly overestimates the experimental total magnetic moment of the U atom and the unit cell volume.     

Estimation of a potential contribution of bed-structure regularization to adsorber downsizing in adsorption gas separation

Five similarity criteria for adsorption systems have been formulated as follows: (1) the ratio of the adsorber length to the thickness of the front; (2) the adsorber output; (3) the relative molar density of the adsorbate at the adsorber inlet; (4) the ratio of the grain saturation time to the residence time of a grain in the front zone; and (5) the Peclet number, composed of the filtration rate, specific size of the filtration area (grain radius or half-width of gaps between sheets), and molecular diffusion coefficient. The values of these criteria change with modification of the tortuosity of transport nanopores. Simple mathematical analysis has shown that the adsorber volume decreases in proportion to the decrease in the nanopore tortuosity induced by bed-structure regularization. The pressure drop through the adsorber, as well as power consumption, will remain unchanged.     

Limiting efficiency of adsorption heat pump

Based on the concept of unrecoverable energy losses in small-scale dissipative structures, the upper limit of the heat pump efficiency has been estimated. This limiting efficiency is achieved in the absence of energy losses due to heat exchange with the heat carrier but when nonequilibrium nonisothermal vapor transfer is taken into account. The limiting efficiency is smaller than the thermodynamically equilibrium efficiency and serves a better reference point in the search for optimal process layout.     

Number of adsorbers for a gas separation system

An algorithm for the total number of adsorbers and the number of active adsorbers (i.e., the ones in the adsorption mode at the moment in question) has been designed in terms of the ergodic hypothesis. This algorithm is intended for the design of gas separation systems.     

The existence of the: exp ϕ:4 quantum field theory in a finite volume

The quantum field theory with an exponential interaction in the four-dimensional space-time in a periodic box is considered. It is shown that the vacuum expectation values exist as tempered distributions and satisfy some Wightman axioms.