Combustion physical transformations

Ageing of glass may also be observed because of the physical transformation of internal defects like metastable nickel sulfide (NiS) inclusions. These imdergo a slow transformation at room temperature from a dense to a less dense phase. These inclusions can be of different compositions, namely NiS, Nii or M7S6 (Barry and Ford, 2001 Yousfi et al., 2010), with sizes in the range 1-100 pm (Barry et ah, 1998). S comes from the raw materials and combustion, while Ni comes from the abrasion of the tools used for batching (Chapter 10). In fact, it remains impossible to eliminate these NiS inclusions. Their content is estimated at about 1 particle for 10 tons of glass. 

Breusov, O.N., Physical-Chemical Transformation of Inorganic Materials Under Shock Waves, in Proceedings, Second All-Union Symposium on Combustion and Explosion (edited by Stesik, L.N.), Chernogolovka, 1971, pp. 289-293, Translation, Sandia National Laboratories Report No. RS3144/79/43. 

Fuels for combustion are initially gases, liquids, or solids. A fuel initially in one phase may be transformed into another during the burning process (i.e., liquids vaporized to gases). The factors involved in the selection of the fuel phase or its physical and chemical characteristics for an application such as burning in an automobile or jet aircraft involve many different considerations such as price, availability, and source. 

Many of the unsolved problems of physics and chemistry were concerned with combustion and detonation. A really well-developed scheme of normal combustion is seldom realized in nature. The most common form of gaseous combustion - turbulent combustion - was found to be the result of the hydrodynamic instability of the combustion process in a flow. Even in the simplest system, the physical scheme of turbulent combustion is very far from being perfectly understood. Just as in the analysis of detonative combustion, it is still possible to speak only of the universal instability of the hydrodynamic process accompanying the chemical transformation of matter. Actually, "turbulence is hardly the term for the result of the manifestation of this instability - the appearance of a multifront shockwave in the detonation front. However, the derivation of a complete physical scheme of detonation (especially in relation to condensed expls) will eventually follow from further research in this field... 

Meanwhile, in 1938 at the AS USSR Institute of Chemical Physics A. F. Belyaev showed that the combustion of liquid explosives occurs in the gas phase after their evaporation. In analogy with this, Ya.B. proposed a theory of combustion of a solid powder (24) according to which the powder is heated in the solid phase and then decomposes, transforming into a gas it is only in the gas phase, at some distance from the surface, that the bulk of the chemical energy is released. Ya.B. also pointed out the peculiar effects of... 

What problems face the theory of combustion The theory of combustion must be transformed into a chapter of physical chemistry. Basic questions must be answered will a compound of a given composition be combustible, what will be the rate of combustion of an explosive mixture, what peculiarities and shapes of flames should we expect We shall not be satisfied with an answer based on analogy with other known cases of combustion. The phenomena must be reduced to their original causes. Such original causes for combustion are chemical reaction, heat transfer, transport of matter by diffusion, and gas motion. A direct calculation of flame velocity using data on elementary chemical reaction events and thermal constants was first carried out for the reaction of hydrogen with bromine in 1942. The problem of the possibility of combustion (the concentration limit) was reduced for the first time to thermal calculations for mixtures of carbon monoxide with air. Peculiar forms of propagation near boundaries which arise when normal combustion is precluded or unstable were explained in terms of the physical characteristics of mixtures. 

The combustion is an extremely complex process including many chemical and physical phenomena of transformation of matter. The need and desire to know and control this process urges man to study its various aspects. Organic polymers are but one example of the multitude of materials used by man. They possess peculiar features and properties which individually affect the material behavior in a critical fire situation. It is, therefore, important to study the flammability characteristics of polymeric materials and the factors affecting them. 

All physical and chemical transformations take time. Some physical phenomena, such as the vaporization at a boiling liquid surface, occurs very rapidly and for all practical purposes are instantaneous. Also, some chemical reactions, such as combustion reactions, are very rapid, but mass transfer and many chemical reactions are very slow by comparison. For such phenomena to occur to the extent desired requires allowing sufficient time, which is achieved by allowing sufficient equipment volume or surface area. Rate equations, then, are necessary to determine equipment sizes. For example, the well-known expression for the rate of heat transfer. 

In analyses of turbulent combustion, it is helpful for various purposes to view the processes in frequency or wave-number spaces instead of in time or physical space. Fourier transforms provide the desired decompositions. Transforms with respect to different variables arise. In working with... 

High-temperature thermal treatment of hazardous waste offers a reduction in volume as well as a conversion of toxic organic constituents to harmless or less harmful forms [1]. However, hazardous metals can neither be generated nor destroyed in the waste thermal process, but they can be transformed both chemically and physically [2]. There is therefore a potential for hazardous metals to emit if they vaporize at high temperatures [3]. Many matals and their salts will form vapors at temperatures reached by flame and post-flame zones of a combustion chamber. When the vapors cool, they condense to form submicron particles, which tend to be relatively difficult to capture in air polution control equipments. These emissions of submicron metallic particles have been identified as one of the greatest health risks associated with waste incineration [4]. 

The crucial event in Lavoisier s career was his realization that air (which nearly everyone believed to be a simple substance defined by its physical, rather than by any chemical, properties) must play a part in chemical transformations - most dramatically those observed in ordinary combustion, the roasting (calcining) of metals, and the reduction of ores or cakes . ... 

The physical differences between inherent and extraneous ash are important not only to those interested in cleaning coal but also to those concerned with the fireside behavior of coal ash. Inherent material is so intimately mixed with coal that its thermal history is linked to the combustion of the coal particle in which it is contained. Therefore, it will most likely reach a temperature in excess of the gas in the immediate surroundings. The close proximity of each species with every other species permits chemical reaction and physical changes to occur so rapidly that the subsequent ash particles formed will behave as a single material whose composition is defined by the mixture of minerals contained within the coal particle. The atmosphere under which the individual transformations take place will, no doubt, approach a reducing environment. Figure 2 illustrates a model of the coal and mineral matter as fed to the combustor and the fate of the minerals after combustion [13]. 

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