Fluid Equilibria in Geothermal Fields

but also O2, H2, CH4, NH3, HjS, and COj), the two solubility branches of the trend, ascending and descending, are virtually straight. Because early experiments on the solubility of gaseous species in water were limited to low T (typically below 50 °C), solubility was described by means of empirical relationships accurately reproducing low-r behavior—for instance, the Benson-Krause equation  

More recently, extension of experiments to high T has allowed the derivation of empirical equations valid over the entire stability field of water. The equation of Potter and Clynne (1978) for noble gases, for instance, is valid in the T range 298 r (K) 647  

In equation 9.100, Aq, A, A2, Aj, A4, and A are empirical constants determined for each noble gas (Table 9.10), p is the density of water, and T, is the fugacity coefficient of gas with deviation parameter Z, which can be calculated as a function of the compressibility factor, as follows (see also eq. 9.16 and 9.22 in section 9.1)  

Still more recently, Giggenbach (1980) proposed simple linear equations relating the molar distribution constants of the main reactive gases to T expressed in Celsius  

These constants, listed in Table 9.11, were derived by Giggenbach (1980) from the respective Henry s constant by applying  

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