Vapor-dominated system

There are three possible mechanisms for generating the strongly acid solution which caused the advanced argillic alteration (1) alteration caused by the vapor-dominated system as inferred by White et al. (1971) (2) alteration caused by the oxidation of H2S near the surface and (3) alteration by volcanic gas and/or hot water condensed from a volcanic gas. Among them, (3) is the most attractive mechanism given the following evidence and considerations. 

White, D.E., Muffler, L.J.P. and Truesdeil, A.H. (1971) Vapor-dominated hydrothermal systems compared with hot water systems. Econ. Geol, 66, 75-97. 

Moore, J. N., Lutz, S. J., Renner, J. L., McCulloch, J., and Petty, S. (2000). Evolution of a Volcanic-Hosted Vapor-Dominated Vent System. GRC Trans. 24, 259-263. 

Say we wish to convert a fossil-fuel, nuclear, or solar energy source into net electrical power. To accompftsh this task, we can use a Rankine cycle. The Rankine cycle is an idealized vapor power system that contains the major components foimd in more detailed, practical steam power plants. While hydroelectric and wind are possible alternative sources, the steam power plant is presently the dominant producer of electrical power. 

As discussed in Chapter 3, at moderate pressures, vapor-phase nonideality is usually small in comparison to liquid-phase nonideality. However, when associating carboxylic acids are present, vapor-phase nonideality may dominate. These acids dimerize appreciably in the vapor phase even at low pressures fugacity coefficients are well removed from unity. To illustrate. Figures 8 and 9 show observed and calculated vapor-liquid equilibria for two systems containing an associating component. 

In distillation towers, entrainment lowers the tray efficiency, and 1 pound of entrainment per 10 pounds of liquid is sometimes taken as the hmit for acceptable performance. However, the impact of entrainment on distiUation efficiency depends on the relative volatility of the component being considered. Entrainment has a minor impact on close separations when the difference between vapor and liquid concentration is smaU, but this factor can be dominant for systems where the liquid concentration is much higher than the vapor in equilibrium with it (i.e., when a component of the liquid has a very lowvolatiUty, as in an absorber). 

When a gas comes in contact with a solid surface, under suitable conditions of temperature and pressure, the concentration of the gas (the adsorbate) is always found to be greater near the surface (the adsorbent) than in the bulk of the gas phase. This process is known as adsorption. In all solids, the surface atoms are influenced by unbalanced attractive forces normal to the surface plane adsorption of gas molecules at the interface partially restores the balance of forces. Adsorption is spontaneous and is accompanied by a decrease in the free energy of the system. In the gas phase the adsorbate has three degrees of freedom in the adsorbed phase it has only two. This decrease in entropy means that the adsorption process is always exothermic. Adsorption may be either physical or chemical in nature. In the former, the process is dominated by molecular interaction forces, e.g., van der Waals and dispersion forces. The formation of the physically adsorbed layer is analogous to the condensation of a vapor into a liquid in fret, the heat of adsorption for this process is similar to that of liquefoction. 

Once the heel has been established in the carbon bed, the adsorption of the fuel vapor is characterized by the adsorption of the dominant light hydrocarbons composing the majority of the hydrocarbon stream. Thus it is common in the study of evaporative emission adsorption to assume that the fuel vapor behaves as if it were a single light aliphatic hydrocarbon component. The predominant light hydrocarbon found in evaporative emission streams is n-butane [20,33]. Representative isotherms for the adsorption of n-butane on activated carbon pellets, at two different temperatures, are shown in Fig. 8. The pressure range covered in the Fig. 8, zero to 101 kPa, is representative of the partial pressures encountered in vehicle fuel vapor systems, which operate in the ambient pressure range. 

A list of oxides in these terms is presented as Table 9.6. Following the logic described, one obtains an exothermic system by choosing a metal whose oxide has a -AH per oxygen atom high on the list to react with a metal oxide that is lower on the list. Indeed, the application of this conceptual approach appears to explain why in the oxidation of lithium-aluminum alloys, the dominant product is Li20 and that A1 does not bum in the vapor phase [9],... 

Surface Control. This situation is characterized by a large activation barrier for condensation. Concentration gradients in both the vapor and condensed phase are lacking. The condensation coefficient a is the dominant quantity. The system can be treated by a well-stirred phase model which leads to a simple exponential decay of the departure of the system from equilibrium (see pp. 18, 19 of Ref. 4). 

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