A contribution to the theory of ferromagnetism

The following gives a brief summary of a paper, which it is hoped to publish in extenso later. It is a contribution to the theory of ferromagnetic crystals, and contains in particular a theoretical explanation of Webster's experimental results

A contribution to the theory of ferromagnetic crystals

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Remarks on a problem in symmetric functions

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A note on generalised mean value theorems

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A process model for underground coal gasification - Part-III: Parametric studies and UCG process performance

Underground gas gasification (UCG) is a clean coal technology which involves in-situ gasification of deep-seated underground coal. The process can be divided in two phases based on state of coal seam and direction of cavity growth. In phase-I, cavity grows mainly in vertical direction while in phase-II it grows in horizontal direction. The in-house simulator developed for both the phases of UCG has been reported earlier Samdani a al. (2016a,b). It incorporates reaction kinetics, flow patterns, spalling, heat and mass transfer effects. In this work, we take further insight and perform parametric studies to examine the effects of different operating conditions, coal properties and design parameters on key performance indicators i.e. exit gas quality, energy generation rates etc. The investigation revealed that the exit gas quality and rate of coal consumption are strong functions of spalling rates and kinetics of reactions; the coal having very low spalling tendency or less reactivity may not be favorable for the UCG process. An important parameter called critical spalling rate has emerged through this analysis. It is the property of given coal above which UCG is sustainable. In addition, model performance is also sensitive to inlet gas temperature, pressure and composition. Optimum performance of UCG is obtained at a steam to oxygen ratio of 2.5 and at the highest possible inlet gas temperature, operating pressure, and oxygen content in the feed. Among the design parameters, the length of outflow channel is very important as it strongly affects both the exit gas calorific value and its fluctuations with time. The predicted effects of different parameters are in accord with the observations during lab-scale UCG experiments and different field trials. This study demonstrates the importance of a process model to determine the best conditions for UCG process and to evaluate feasibility of the process for a coal seam under consideration

Stabilization of pyrolysis oil: Comparison of reactive distillation and reactive chromatography

The present study, evaluates the applicability of reactive distillation and reactive chromatography for stabilization of bio-oil, obtained from pyrolysis of wood. Bio-oil, along with several oxygenated organic compounds, contains substantial amounts of carboxylic acids (e.g., acetic acid, 5-10%). The presence of acids results in a shorter shelf life of bio-oil, as it catalyzes condensation reactions of furfural-like components leading to an increase in viscosity over a time period. Thus, we investigate the ability of multifunctional reactor for stabilization of bio-oil through esterification of acid with suitable alcohol in the presence of ion-exchange resin catalyst. Reactive distillation is performed at higher a temperature which is dictated by the bubble point of the mixture, reactive chromatography allows one to perform reaction at relatively low temperatures and with lower alcohols. It results in an improvement in the characteristic properties of bio-oil, thereby increasing the shelf life. The main limitation of this approach is that the catalyst used for esterification also catalyzes simultaneous polymerization of furfural-like components which deactivate the catalyst. Deactivation of Amberlyst-15 with ethanol after 20 h of continuous run in a fixed-bed chromatographic-reactor was found to be less compared to RD making RC a promising candidate for this particular application. (C) 2015 Elsevier B.V. All rights reserved

An application of Tschebyscheff Polynomials to a problem in symmetric functions

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A process model for underground coal gasification - Part-II growth of outflow channel

Underground Coal Gasification (UCG) is a process of gasifying coal in-situ to produce syn-gas. The gas thus produced, passes through the outflow channel that leads to the production well. As explained in part-I of this paper (Samdani et al., 2015), UCG can be divided in two distinct phases. The phase-I corresponds to initial vertical growth of the cavity and the output from phase-I model provides input to the phase-II model. This paper presents an unsteady state model for phase-II of UCG, wherein, the growth occurs in the horizontal direction towards the production well through the outflow channel. A compartment model, based on tracer studies performed on actual UCG cavity, is developed for phase-II of UCG. Here, the outflow channel is divided in small sections along the length, each consisting of rubble zone, void zone and roof at the top. This reduces the complexity caused by non-ideal flow patterns and changing sizes of different subzones inside the outflow channel. The subzones and the sections are linked appropriately, for mass and energy flow, to give overall performance of UCG. The proposed approach combines chemical reactions, heat and mass transfer effects, spalling characteristic and complex flow patterns to achieve meaningful results. In all, seven gas species, three solid species and eleven reactions are included. The simulation results such as variation in solid density, dynamics of different zones, exit gas quality are presented. The model is validated by comparing the predicted exit gas quality and that observed during similar laboratory scale experiments. Finally the results are also compared with pilot scale field-trials. This model along with the phase-I model provides a complete modeling solution for UCG process. (C) 2016 Elsevier Ltd. All rights reserved