CHAPTER 13. Ultrasonics 2: High Pressure Speed of Sound, Isentropic Compressibility

Abstract

The pressure-volume (density)-temperature (P-r-T) surface of a fluid presents the basic thermodynamic properties for investigating the behaviour of fluids. The isothermal compressibility, k T , and isentropic (adiabatic) compressibility, k S , of a fluid are defined as:(13:1)where r refers to the specific molar volume, P to pressure, T to temperature and S to entropy. The pioneering studies on the P-r-T relationships for various compounds were conducted by Bridgman, 1,2 Gibson and Kincaid 3,4 and many colleagues in the early 20th century. Today, the experimental P-r-T data of a large number of liquids and/or mixtures have been stored or published in a variety of styles. Examples include the databases of Volume Properties: Liquids, Solutions and Vapours Edited by Emmerich Wilhelm and Trevor M. Letcher

Gibbs Energy and Helmholtz Energy

“…the molar heat capacity at constant pressure is defined by eqn (1.139) and with eqn (1.163) we obtain .190) in high-pressure research, [136][137][138][139][140][199][200][201][202][203][204][205][206] eqn (1.189) and (1.190) are particularly interesting. For instance, the pressure dependence of C P of a constantcomposition fluid may be determined either from PVT data alone or by high-pressure calorimetry or by transitiometry, 136,137 or by measuring the speed of ultrasound at sufficiently low frequency as a function of P and T, 138,199,201,202,[204][205][206][207][208][209][210][211] and the consistency of the experimental results can be ascertained in various ways. Starting from…”

“…to an excellent approximation, i.e. neglecting dissipative processes due to shear viscosity η s , thermal conductivity λ, bulk viscosity η v , etc., v 0 may be treated as an intensive thermodynamic equilibrium property 32,138,[207][208][209][210][211][212][213][214][215] related to β S via eqn (1.207). alternatively, by using the relations provided by eqn (1.131) and (1.132), we have…”