Adsorption isotherms of hydrogen and deuterium have been measured a t temperatures of 75-90" I< and pressures up to 760 mm Hg on the following six adsorbents: charcoal (2), silica gel, and Linde molecular sieves type 411, 5A, and 13X.Deuterium was found to be adsorbed to a greater extent than hydrogen in all cases investigated, its isosteric heat of adsorption exceeding that of hydrogen by 50 t o 300 cal/mole.Binary adsorption isother~ns were determined on the same adsorbents in the range 10-90%Dz at temperatures of 75 and 90' K and a total pressure x of 750 and 200 mm Hg. The analyses were performed by the thermal conductivity method using thermistor sensing elements in a static system a t atmospheric pressure. The device proved of exceptional stability, requiring no recalibrations and yielding an analytical accuracy of better than 0.02% deuterium content. The binary separation factors ol were found t o be constant over the concentration range investigated, with values for a varying from about 1.25 on charcoal to 2.54 on type 4A molecular sieves a t 75' I< and 750 mm Hg. The results suggest that the variations in cu are due mainly to differences in chemical composition of the adsorbents rather than pore size, surface area, or origin of the materials.
The adiabatic desorption of single gaseous components from a fixed bed of solids by a constant pressure gas purge is analyzed in detail using equilibrium theory. The analysis is carried out within the framework of industrial practice using the system C02-Nn-SA molecular sieves as an example. The parameters investigated include the use of adsorber feed and pure product gas as regenerant, and the effect of purge gas temperature and heat capacity, total system pressure, and adsorber feed concentration on the regeneration process. It is shown that the amount of purge gas and adsorber feed treated per unit weight of bed are equal to the relevant slopes of the "characteristics" or "shock chords" on a solid concentration-gas concentration characteristic diagram (hodograph). A simple analysis of the desorption process is thus made possible which is used to arrive at some important conclusions regarding the effect of the parameters on desorption time, regenerant consumption, and the economics of the process. Conditions under which residual solute may be removed from a hot bed advantageously with either cold clean gas or cold adsorber feed are outlined.
The paper presents a mathematical analysis of the contributions of flow and mass transport to a single reactive event at a blood vessel wall. The intent is to prepare the ground for a comprehensive study of the intertwining of these contributions with the reaction network of the coagulation cascade. We show that in all vessels with local mural activity, or in "large" vessels (d greater than 0.1 mm) with global reactivity, events at the tubular wall can be rigorously described by algebraic equations under steady conditions, or by ordinary differential forms (ODEs) during transient conditions. This opens up important ways for analyzing the combined roles of flow, transport, and coagulation reactions in thrombosis, a task hitherto considered to be completely intractable. We report extensively on the dependence of transport coefficient kL and mural coagulant concentration Cw on flow, vessel geometry, and reaction kinetics. It is shown that for protein transport, kL varies only weakly with shear rate gamma in large vessels, and not at all in the smaller tubes (d less than 10(-2) mm). For a typical protein, kL approximately 10(-3) cm s-1 within a factor of 3 in most geometries, irrespective of the mural reaction kinetics. Significant reductions in kL (1/10-1/1,000) leading to high-coagulant accumulation are seen mainly in stagnant zones vicinal to abrupt expansions and in small elliptical tubules. This is in accord with known physical observations. More unexpected are the dramatic increases in accumulation which can come about through the intervention of an autocatalytic reaction step, with Cw rising sharply toward infinity as the ratio of reaction to transport coefficient approaches unity. Such self-catalyzed reactions have the ability to act as powerful amplifiers of an otherwise modest influence of flow and transport on coagulant concentration. The paper considers as well the effect on mass transport of transient conditions occasioned by coagulation initiation or pulsatile flow. During initiation, instantaneous flux varies with diffusivity and bulk concentration, favouring the early adsorption/consumption of proteins with the highest abundance and mobility. This is akin to the 'Vroman effect' seen in narrow, stagnant spaces. The effect of flow pulsatility on kL has the potential, after prolonged cycling, of bringing about segregation or accumulation of proteins, with consequences for the coagulation process.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.