Phase changes in industry

Before the steam engine was invented, there were no automatic pumps to draw well water or engines to propel cars or trains. Since their conception in the 1660s, steam engines have evolved, been improved, and, in some cases, even been replaced, but they are still very much a part of industrial society. 

The first widely used industrial steam engine, the Watt Steam Engine, invented in 1765, used evaporation and condensation to efficiently create energy. Fire was used to boil water in an enclosed space to produce steam. The Watt Steam Engine was an external combustion engine because of the external source of fuel. In this case, the fire burned outside of the engine itself. 

The expanding steam from the boiling water was directed to a cylinder where it pushed on pistons, causing them to move. In the cylinder, the force of the expanding steam drove the pistons up. The pistons, in turn, moved beams or gears to do the work. 

As the steam lost energy, it was collected in a separate chamber where it cooled and condensed back into liquid water. In the process of condensing in a sealed chamber, the steam created a vacuum, a space empty of matter. This vacuum allowed atmospheric pressure to drive the piston down again, preparing it for another round of work. 

boats and trains powered by steam are not widely used. Most transportation steam engines have been replaced by internal combustion engines, which burn fuel inside the engine 

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Desalination. Desalination of seawater and brackish water has been and, as of the mid-1990s, is the primary use of RO. Driven by a need for potable water in areas of the world where there is a shortage, this industry has developed. Desalination involves the reduction of the total dissolved soHds (IDS) concentration to less than 200 mg/L. RO offers several advantages over other possible desalination processes such as distillation (qv), evaporation (qv), and electro dialysis. The primary advantage of RO over the traditionally used method of distillation is the energy savings that is afforded by the lack of a phase change in RO. 

The rate at which PBDE concentrations have increased in the environment and in humans has been of considerable interest. Temporal trend studies from Europe have indicated that PBDE levels in human milk increased markedly from 1972 to 1997, doubling every 5 years [38]. Since 1997, the PBDE levels in human milk have decreased somewhat [39]. These recent ameliorations may be the result of changes in industrial practices in Europe. The European Commission, for example, has phased out the use of the commercial penta-BDE product because of concerns about its potentially adverse human health effects. Now, > 95% of the current global demand for the penta-BDE product... 

In praetiee, for heat transfer reasons, it is often desirable to vaporize the substanee from the hquid state, so the complete series of phase changes in an industrial subhmation process can be solid liquid vapour sohd. It is on the condensation side of the process that the appearance of the liquid phase is prohibited. The supersaturated vapour must condense directly to the crystalline solid state. 

Gibson, P. (1999), Review of numerical modeling of convection, diffusion, and phase change in textiles , in Computational technologiesforfluid/thermal/structural/chemical systems with industrial applications, Kleijn, C. and Kawano, S. (Eds), New York, USA, vol. 397-2, ASME PVP, pp. 117-26. 

Many industrial separation technologies also rely on accurate knowledge of phases. One of the oldest chemical technologies, soapmaking, depends directly on recognizing and inducing phase changes in order obtain the desired product... 

Catalytic gas-phase reactions play an important role in many bulk chemical processes, such as in the production of methanol, ammonia, sulfuric acid, and nitric acid. In most processes, the effective area of the catalyst is critically important. Since these reactions take place at surfaces through processes of adsorption and desorption, any alteration of surface area naturally causes a change in the rate of reaction. Industrial catalysts are usually supported on porous materials, since this results in a much larger active area per unit of reactor volume. 

In addition to the reduction in performance, flow maldistribution may result in increased corrosion, erosion, wear, fouling, fatigue, and material failure, particularly for Hquid flows. This problem is even more pronounced for multiphase or phase change flows as compared to single-phase flows. Flow distribution problems exist for almost all types of exchangers and can have a significant impact on energy, environment, material, and cost in most industries. 

It is not always necessary for the resin to be in the hydrogen form for adsorption of cations, especiaHy if a change in the pH of the Hquid phase is to be avoided (see also Hydrogen-ION activity). Eor example, softening of water, both in homes and at industrial sites, is practiced by using the resin in the form. 

The simple model given above does not take account of the facts that industrial refractories are poly crystalline, usually non-uniform in composition, and operate in temperature gradients, both horizontal and vertical. Changes in the coiTosion of multicomponent refractories will also occur when there is a change in the nature of tire phase in contact with the conoding liquid for example in Ca0-Mg0-Al203-Cf203 refractories which contain several phases. 

Although many industrial reactions are carried out in flow reactors, this procedure is not often used in mechanistic work. Most experiments in the liquid phase that are carried out for that purpose use a constant-volume batch reactor. Thus, we shall not consider the kinetics of reactions in flow reactors, which only complicate the algebraic treatments. Because the reaction volume in solution reactions is very nearly constant, the rate is expressed as the change in the concentration of a reactant or product per unit time. Reaction rates and derived constants are preferably expressed with the second as the unit of time, even when the working unit in the laboratory is an hour or a microsecond. Molarity (mol L-1 or mol dm"3, sometimes abbreviated M) is the preferred unit of concentration. Therefore, the reaction rate, or velocity, symbolized in this book as v, has the units mol L-1 s-1. 

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