A fluidized-bed combustion process with inherent CO2 separation; Application of chemical-looping combustion

A fluidized bed combustion process with inherent CO2 separation; application of chemical looping combustion

Swelling/deswelling of anionic copolymer gels

Abstract Despite its widespread use in petrophysics, tortuosity remains a poorly understood concept. Tortuosity can have various meanings when used by physicists, engineers or geologists to describe different transport processes taking place in a porous material. Values for geometrical, electrical, diffusional and hydraulic tortuosity are in general different from one another. Electrical tortuosity is defined in terms of conductivity whereas hydraulic tortuosity is usually defined geometrically, and diffusional tortuosity is typically computed from temporal changes in concentration. A better approach may be to define tortuosity in terms of the underlying flux of material or electrical current with respect to the forces which drive this flow. Unsteady transport processes, including diffusion, can be described only by a population of tortuosities corresponding to the different flow paths taken by particles traversing the medium. In measurements of steady flow (e.g., those normally used to obtain resistivity or permeability), information about particle travel times is lost, and so the multiple values of tortuosity are homogenised. It can be shown that the maximum amount of information about pore structure is embedded in transport processes that combine advective and diffusive elements. Most existing formulations of tortuosity are model-dependent, and cannot be correlated with independently measurable pore-structure properties. Nevertheless, tortuosity underpins the rigorous relationships between transport processes in rocks, and ties them with the underlying geometry and topology of their pore spaces. Tortuosity can be redefined in terms of the energetic efficiency of a flow process. The efficiency is related to the rate of entropy dissipation (or isothermally, energy dissipation) with respect to a simple, non-tortuous model medium using the postulates of non-equilibrium thermodynamics. Through Onsager’s reciprocity relation for coupled flows it is possible to inter-relate efficiency for pairs of transport processes, and so go some way towards unifying tortuosity measures. In this way we can approach the goal of predicting the value of one transport parameter from measurements of another.

Tortuosity: a guide through the maze

Time-dependent models of the thermal and diffusive behavior of the Martian regolith are developed to investigate the stability of ground ice within the top several meters of the regolith. The geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation are included in calculations of surface and subsurface temperatures between +/- 60 deg latitude. Ground ice is found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point. Calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between +/- 60 deg latitude at low obliquity. The time scales for condensation of ground ice are found to be comparable to that of orbital oscillations, suggesting that the present geographic distribution of ground ice may depend on the orbital history of Mars.

Geographic variations in the thermal and diffusive stability of ground ice on Mars

Oxygen diffusion and microbial activity in the composting of dehydrated sewage sludge cakes

The effect of pore necking on Knudsen diffusivity and collision frequency of gas molecules with pore walls

Characteristics of Reduction and Oxidization Cyclic Process by Use of αFe2O3 Medium

The swelling behavior of poly(acrylamide-co-acrylic acid and trimethyl-N-acryloyl-3-aminopropyl ammonium chloride) gel in electrolyte solutions of NaCl (uni-univalent) and MgCl2 (bi-univalent) was investigated over the whole range of pH.The swelling of gel was induced by the ionic pressure due to Na+ and/or Mg2+ ions in the acid region (pH = 4–7) as well as basic region, where Na+ or Mg2+ ions added in solution were exchanged with H+ ion supplied by the yet undissociated group, –COOH. in the region of pH = 1–4, Cl– ions generated the ionic pressure. In the case of bivalent cation, Mg2+ especially, it was observed that the interactions between the localized fixed charges and the bivalent cation, may result in formation of new weak cross-linking. The swelling and behavior of the ions in the gel were predicted fairly well using a simple model based on Donnan equilibrium theory.

Yoshio Nakano

Papers

Oxygen diffusion and microbial activity in the composting of dehydrated sewage sludge cakes

The effect of pore necking on Knudsen diffusivity and collision frequency of gas molecules with pore walls

Characteristics of Reduction and Oxidization Cyclic Process by Use of αFe2O3 Medium

Behavior of ions within hydrogel and its swelling properties.

EFFECT OF pH ON THE PHASE TRANSITION OF N-ISOPROPYLACRYLAMIDE-SODIUM ACRYLATE COPOLYMER GEL