Fractionation of air

Foams for firefighting appHcations are typically made from a concentrated foaming agent diluted with water and then mixed with air. Rather than consider the volume fraction of air in the foam, firefighting foams are characterized by their expansion ratio, which is the increase in volume of the Hquid after the foam is formed. Expansion ratios range from 5 1 to over 1000 1 ratios of 5 1 to 20 1 are called low expansion ratios of 21 1 to 200 1, medium expansion and ratios greater than 200 1, high expansion. 

Air needs to be dissolved in water under pressure at 20°C for use in a dissolved-air flotation process (see Chapter 8). The vapor-liquid equilibrium between air and water can be predicted by Henry s Law with a constant of 6.7 x 104 bar. Estimate the mole fraction of air that can be dissolved at 20°C, at a pressure of 10 bar. 

Model calculations allow one to evaluate POP trans-boundary transport between European countries. The contributions of external sources to PCDD/Fs air concentrations in some European countries including Eastern European countries (given in black) are shown in Figure 9(a). In spite of the general decrease of contamination in Europe, the role of trans-boundary transport is yet essential. The fraction of air concentrations caused by external sources amounts approximately to 60% for Hungary, Romania and Slovakia. As it was mentioned above air contamination by PCDD/Fs is partly explained by accumulation in media with subsequent re-emission. The fraction of concentrations caused by this process can reach 10-15% in some countries (Figure 9(b)). 

The gas ballast pump has the function of pumping the fraction of air, which is often only a small part of the water-vapor mixture concerned, without simultaneously pumping much water vapor. It is, therefore, understandable that, within the combination of condenser and gas ballast pump in the stationary condition, the ratios of flow, which occur in the region of rough vacuum, are not easily assessed without further consideration. The simple application of the continuity equation is not adequate because one is no longer concerned with a source or sink-free field of flow (the condenser is, on the basis of condensation processes, a sink). This is emphasized especially at this point. In a practical case of non-functioning of the condenser - gas ballast pump combination, it might be unjustifiable to blame the condenser for the failure. 

Figure 2. Capillary-column gas chromatogram of the total polynuclear hydrocarbon fraction of air-particulate matter ). Conditions 11 m X 0.26 mm -i.d. glass capillary coated with SE-52 methylphenylsilicone stationary phase see Table 1 for...

The mole fractions of air have been simulated as 0.21 and 0.79 for 02 and N2 respectively. The two parameters, S/C, O/C (oxygen to carbon) ratios have been used to analyze the reforming reactors effectively. These two relationships can be written as follows ... 

Now calculate the composition of the vapor. y3 represents the mole fraction of air in the vapor. 

Cumulative exposure level (values in [ ]) Typical concentration [0.1 f/mL] x Working life span [40 years] x Fraction of air breathed in workplace [8 m /day/20 m /day x 5 days/7 days x 49 weeks/52 weeks]... 

Determine Ihe mole fraction of air dissolved in waler at the surface of a lake whose temperature is 17°C (Fig, 14-17). Take the atmospheric pressure at lake level to he 92 kPa. 

SOLUTION The mole fraction of air dissolved in water at the surface of a lake is to be determined. 

Note that v/ith little loss in accuracy (an error of about 2 percent), we could have ignored the vapor pressure since the amount of vapor in air is so small, Then the mole fraction of air in the water becomes... 

The mass fraction of air at the bottom of the tube is very small, as shown above, and thus the density of the mixture at x = 0 can simply be taken to be the density of helium, vvhich is... 

Consider a glass of water in a room at 20°C and 100 kPa. If the relative humidiiy in the room is 70 percent and the water and ihe air are at the same temperature, determine (a) the mole fraction of the water vapor in ihe room air, (6) the mole fraction of the water vapor in the air adjacent to the water surface, and (c) the mole fraction of air in the water near the. surface. 

The first experimental evidence for the noble gases was obtained by Henry Cavendish in 1766. In a series of experiments on air, he was able to sequentially remove nitrogen (then known as phlogisticated air ), oxygen ( dephlogisticated air ), and carbon dioxide ( fixed air ) from air by chemical means, but a small residue, no more than one part in 120, resisted all attempts at reaction. The nature of Cavendish s unreactive fraction of air remained a mystery for more than a century. This fraction was, of course, eventually shown to be a mixture of argon and other noble gases. ... 

If one wishes to calculate the mole fraction of air dissolved in the water, then Raoult s law caimot be applied, because the critical temperature of air is much lower than 298.15 K (25°C). This problem can be solved by Hemy s law, applied here for pressures low enough tliat the vapor phase may be assumed an ideal gas. For a species present as a very dilute solute in the hquid phase, Henry s law then states that the partial pressure of the species in the vapor phase is directly proportional to its liquid-phase mole fraction. Thus,... 

Nitrogen is taken from air or from the nitrogen content of natural gas. This is carried out by low temperature fractionation of air, which is preferred when pure oxygen is required as an oxidizing agent in the production of synthesis gas. Alternatively air is employed directly in the production of synthesis gas and the oxygen is removed by the to be oxidized reaction partners. 

With the aid of steam tables, the reader should now be able to find the mole fractions of air and water in an air-water system, given only the temperature, T, plus either... 

In all three of these examples, the mole fraction of air, y, is found by subtracting from unity. 

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