Phase Equilibria and Static Properties

Abstract

The state condition of a fluid is described as a function of two intensive properties and the properties of the fluid can be represented also as a function of two independent properties. Figure 2.1.1 [1] shows the PVT surface of water in which the relation of pressure, volume and temperature of water is described. The critical point is shown as an open circle labeled C.P. The critical temperature of water is T C = 647.096 K, the critical pressure is P C = 22.064 MPa and the critical volume is V C= 0.003106 m3/kg. A list of critical and basic constants for selected fluids is given in Appendix A. The saturated liquid line and the saturated vapor line meet at the critical point. The dome-shaped region under the saturated liquid and vapor lines is the two-phase coexistence region of liquid and vapor. The region above the dome-shaped region is a single-phase homogeneous region which may be divided into three regions by the critical isotherm and critical isobar. The region at high pressure and low temperature is the compressed liquid region and the region at high temperature and low pressure is the superheated vapor or gas region. The supercritical fluid (SCF) region covers the states at which temperature is higher than the critical temperature, and pressure is higher than the critical pressure. In the SCF region, the phase separation can no longer be observed by compression of the vapor or expansion of the liquid.