Thermophysical Properties at Critical and Supercritical Pressures

Abstract

Critical point (also called a critical state) is a point in which the distinction between the liquid and gas (or vapour) phases disappears, i.e., both phases have the same temperature, pressure and volume or density. The critical point is characterized by the phase-state parameters T cr , P cr and V cr (or ρ cr), which have unique values for each pure substance. Near-critical point is actually a narrow region around the critical point, where all thermophysical properties of a pure fluid exhibit rapid variations. Pseudocritical line is a line, which consists of pseudocritical points. Pseudocritical point (characterized with P pc and T pc) is a point at a pressure above the critical pressure and at a temperature (T pc > T cr) corresponding to the maximum value of the specific heat at this particular pressure. Supercritical fluid is a fluid at pressures and temperatures that are higher than the critical pressure and critical temperature. However, in the present chapter, a term supercritical fluid includes both terms-a supercritical fluid and compressed fluid. Supercritical "steam" is actually supercritical water, because at supercritical pressures fluid is considered as a single-phase substance. However, this term is widely (and incorrectly) used in the literature in relation to supercritical "steam" generators and turbines. Superheated steam is a steam at pressures below the critical pressure, but at temperatures above the critical temperature.

Why Deep-Water Eruptions Are So Different From Subaerial Eruptions

“…At 1 and 2 km water depth, the hydrostatic pressures are ∼10 and 20 MPa, and the gas pressure in bubbles would have to be >15 MPa and >25 MPa, respectively, in order to initiate an explosive eruption. However, 25 MPa is well above the critical pressure of water, and consequently the exsolved magmatic water in the magma would be supercritical, or pseudo-critical fluid with an extremely low expansivity factor (<<<0.1; Pioro and Mokry, 2011).…”

Application of Supercritical Pressure in Power Engineering

“…The general trends of various properties near the critical and pseudocritical points [8,19,20] can be illustrated on a basis of those of water and carbon dioxide (Figures 11.6e11.10). Properties of supercritical helium and R-134a are shown in Ref.…”

Diameter Effect on the Wall Temperature Behaviors During Supercritical Water Heat Transfer Deterioration in Circular Tubes and Annular Channels

“…The supercritical water reactor (SCWR) is one of the six generation IV nuclear systems. One advantage of SCWR is to increase the nuclear power plants thermal efficiency, which is now about 36-38%, to about 45-50% (Pioro and Mokry, 2011). Because no phase change occurs for supercritical water, SCWR can reduce the capital and operational costs through eliminating steam related facilities (Cheng et al, 2003;Pioro and Duffey, 2005).…”

“…Because no phase change occurs for supercritical water, SCWR can reduce the capital and operational costs through eliminating steam related facilities (Cheng et al, 2003;Pioro and Duffey, 2005). Pioro and Mokry (2011) provided the pressure-temperature diagram of water (Figure 1). The critical temperature and critical pressure of water are 373.95 and 22.06 MPa, respectively.…”

“…Figure 2 shows the thermophysical properties of water at 25.3 MPa. Because of the strong variation of the thermophysical properties in the area near the pseudocritical point, the characteristics of supercritical water heat transfer are quite different from FIGURE 1 | Pressure-temperature diagram of water, reprinted from Pioro and Mokry (2011) with permission of IntechOpen. subcritical water (Shitsman, 1963;Cheng et al, 2003Cheng et al, , 2007Hu and Gu, 2018;Xiao et al, 2018).…”