Internal pressure of liquids from the calorimetric measurements near the critical point

Abstract

A new relation between the internal pressure and isochoric heat capacity jump of liquids along the coexistence curve near the critical point was found. Our previously reported one- and two-phase isochoric heat capacities and specific volumes at saturation were used to calculate internal pressure of molecular liquids (water, carbon dioxide, alcohols, n-alkanes, DEE, etc.).The internal pressure derived from the calorimetric measurements was compared with the values calculated from the reference (NIST, REFPROP) and crossover equations of state. Locus of the isothermal and isochoric internal pressure maxima and minima was studied using calorimetric data and the reference and crossover equations of state near the critical point. The maximum of the internal pressure of light and heavy water around the temperature of 460K along the liquid saturation curve was found. We also found very simple relation between the internal pressure, ΔPintsat, and isochoric heat capacity, ΔCV, jumps near the critical point.