The application of the virial equation to determine values for the virial coefficients requires a knowledge of the pressure, volume, temperatme and the number of moles of the gas. It is generally assumed that for pressures below 0.1 MPa, terms beyond the second virial coefficient can be neglected. For a fixed mass of gas, measurements are usually made of the pressure when the gas either occupies different known volumes at constant temperatme, or is heated to different known temperatmes at constant volume. [Pg.5]

Application of an infinite series to practical calculations is, of course, impossible, and truncations of the virial equations are in fact employed. The degree of truncation is conditioned not only by the temperature and pressure but also by the availability of correlations or data for the virial coefficients. Values can usually be found for B (see Sec. 2), and often for C (see, e.g., De Santis and Grande, ATChP J., 25, pp. 931-938 [1979]), but rarely for higher-order coefficients. Application of the virial equations is therefore usually restricted to two- or three-term truncations. For pressures up to several bars, the two-term expansion in pressure, with B given by Eq. (4-188), is usually preferred [Pg.529]

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