Thermodynamics Table of Contents

At a pressure of 3206.2 psia, represented by line MNO, there is no constant-temperaturevaporization process. Rather, point N is a point of inflection, with the slope being zero. Thispoint is called the critical point, and at the critical point the saturated-liquid and saturated-vaporstates are identical. The temperature, pressure, and specific volume at the critical point are calledthe critical temperature, critical pressure, and critical volume.A constant pressure process greater than the critical pressure is represented by line PQ. Thereis no definite change in phase from liquid to vapor and no definite point at which there is achange from the liquid phase to the vapor phase. For pressures greater than the critical pressure,the substance is usually called a liquid when the temperature is less than the critical temperature(705.47°F) and a vapor or gas when the temperature is greater than the critical temperature. Inthe figure, line NJFB represents the saturated liquid line, and the line NKGC represents thesaturated vapor line.