TABLE OF CONTENTS The emergence of powerful desktop computers has made the design engineer's life significantly easier. No longer do engineers have to rely on the approximate hand calculation methods, such as those provided earlier for hydrate formation estimates. In addition, a wider spectrum of additional calculations is available to them. This is true for hydrate calculations, where several software packages are available.
The bases of these computer programs are the rigorous thermodynamic models found in the literature. Three of the more popular ones are briefly reviewed here. This is followed by a brief discussion of the use of some of the available software packages.
As mentioned previously, one of the problems in the study of gas hydrates is the observation that they were nonstoichiometric. First, scientists had to come to terms with this as an observation. Any model for hydrate formation had to handle this somewhat unusual property. Next, the fact that there is more than one type of hydrate had to be addressed. Rigorous models would have to distinguish between the various types of hydrates.
The criteria for phase equilibrium, which were established more than 100 years ago by Gibbs, are that (1) the temperature and pressure of the phases are equal; (2) the chemical potentials of each of the components in each of the phases are equal; and (3) the global Gibbs free energy is a minimum. These criteria apply to phase equilibrium involving hydrates and form the basis for the models for performing hydrate equilibrium calculations.
