Real Processes and Gases

Compression in reciprocating and centrifugal compressors is essentially adiabatic but it is not frictionless. The pressure-volume behavior in such equipment often conforms closely to the equation 

Such a process is called polytropic. The equation is analogous to the isentropic equation (7.20) but the polytropic exponent n is different from the heat capacity ratio k. 

Polytropic exponents are deduced from PV measurements on the machine in question. With reciprocating machines, the PV data are recorded directly with engine indicators. With rotary machines other kinds of instruments are used. Such test measurements usually are made with air. 

Work in polytropic compression of a gas with equation of state PV = zRT is entirely analogous to Eq. (7.26). The hydrodynamic work or the work absorbed by the gas during the compression is 

Manufacturers usually characterize their compressors by their polytropic efficiencies which are defined by 

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It follows that the efficiency of the Carnot engine is entirely determined by the temperatures of the two isothermal processes. The Otto cycle, being a real process, does not have ideal isothermal or adiabatic expansion and contraction of the gas phase due to the finite thermal losses of the combustion chamber and resistance to the movement of the piston, and because the product gases are not at tlrermodynamic equilibrium. Furthermore the heat of combustion is mainly evolved during a short time, after the gas has been compressed by the piston. This gives rise to an additional increase in temperature which is not accompanied by a large change in volume due to the constraint applied by tire piston. The efficiency, QE, expressed as a function of the compression ratio (r) can only be assumed therefore to be an approximation to the ideal gas Carnot cycle. 

Depending on the character of the inflaming material, the conditions of the pyrolysis process and the properties of the EC- residence medium, their surface can be covered with adsorbed substances. Often these ate hydrophobic, incompletely burnt, hydrocarbons. However, the cover may happen to be hydroscopic (due to adsorption of atmospheric gases), ready to form hydrogen and coordinate bonds. Pure EC is absolutely inert at usual temperatures. This is an hydrophobic, insoluble substance (it may be oxidized at about 600 C or in the atmosphere of F2, but such conditions do not occur in the real atmosphere). EC is capable of reacting with radicals, which may be essential from the viewpoint of the chemical reactions taking place in the atmosphere. The EC catalytic activity in reactions of atmospheric SO2 oxidation has been reported in [29]. These reactions can be driven by two mechanisms dry (in the presence of water) and moist , when an EC particle is filmed with water. The moist mechanism is more effective [10]. 

In this paper, and with the aim of being closer to the real conditions found in combustion processes flue gases, the influence on Phe adsorption of another important eomponents present in these waste streams, steam and CO2, is studied within the eoneentration ranges normally emitted. 

The / -F-T behaviour of real gases is a topic that has concerned physicists and chemists for more than a century. Some of this interest has arisen from the importance of the study of gas imperfections in the elucidation of the forces between molecules. From a more practical point of view, knowledge of p-V-T relationships is essential for the resolution of problems in chemical engineering processes where gases are present. 

The positive value indicates that work must be done on the mixture to achieve an isobaric separation. In a real isothermal-isobaric separation of ideal gases, more than this minimum amount of work would be needed, because a real process would be irreversible. Moreover, when separating real mixtures (whose components have inter-molecular forces), the total minimum work would not be given by (4.1.47). However, it could still be determined from O using (4.1.46), provided a reliable model were available for the Gibbs energy of the mixture and each pure. Expressions for G of real mixtures would be more complicated than the ideal-gas expression (4.1.47) but such expressions could be obtained from model equations of state. 

In spite of the advances made in the past years, there is still a large gap between the lab-scale and the real application in the industry. Efforts are focused on the development of new man-branes that enhance the process efficiency. This is a long and expensive process, and very few membrane materials and modules are commercially available. In addition, there is a lack of information on the effectiveness of those manbranes in a longterm and under industrial conditions (gas feed conposilion, temperature, and pressure). Mainly, the effect of common gases such as H2S, SO2, NH3, water, and ashes are not (deeply) studied, which indeed limits the extrapolation of results to an industrial scenario. This creates uncertainty about the applicability of those systems in the industry and makes the decision-making... 

On these bases, further research in the field would focus on the development of new membranes that fit in the framework of low-cost processes. In fact, to consider an economically affordable replacement of membranes, the development of new solvents (when involved) for CO2 capture with low vapor pressure and low toxicity, the study of process performance under industrial operation conditions (real composition regarding gases such as H2S, SO2, NH3, and water, temperature, and pressure) is necessary to achieve a real implementation in the industry [177,178]. 

Knowledge on the concentrations of active solvent component(s) and absorbed gases are of high importance for acid gas removal processes, such as natural gas processing and CO2 capture from flue gas. Real-time information of these parameters is currently unavailable. This paper presents recent progress on the development of a promising method that combines in-line measurements with multivariate modelling in order to enable this. 

The term industrial gases is herewith intended to include also the category of medical gases , which, while being produced by means of industrial processes, have meanwhile become real drugs and are subject to Good Manufacturing Practices. 

The same equation applies in the isothermal formation of an ideal solution, while real gases and real solutions will be considered in Chapter 11. Returning to Eq.3.12.8 we notice that, since all y s are less than one, the mixing process leads to an increase in entropy. This, of course, should be expected. Mixing is a natural (spontaneous) process, and as such it leads to an entropy increase. 

Gas sensors are of importance for a variety of environmental, industrial, medical, scientific and even domestic applications. The gas may be, for example, hazardous to human health, an atmospheric pollutant, or important, in terms of its concentration, for an industrial or medical process. Apart from systems merely providing an alarm signal, it is frequently required to obtain accurate real-time measurements of the concentration of a particular target gas, often in a mixture of other gases. 

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