THE EQUATION OF STATE OF WATER TO 250-DEGREES-C AND 200-MPA OBTAINED FROM A HIGH-PRESSURE DILATOMETER

We have evaluated the performance of a commercially available, completely automated high pressure dilatometer (PVT apparatus) by determining the equation of state of water over the ranges 30-degrees-C-250-degrees-C and 0-200 MPa, using a sample of only 1-2 g. Although the apparatus was designed for the measurement of solid and molten polymers, we conclude that the system is quite capable of measuring PVT properties of water (and presumably other simple liquids) with a reasonable accuracy (0.001 to 0.005 cm3/g, depending on the temperature range), typically five to ten times less accurate than dedicated equipment using 40-250 times larger samples and, in general, smaller pressure and temperature ranges. Two polynomial fits (for separate pressure ranges) with twelve coefficients give 0.0004-0.0005 cm3/g absolute average deviations from the experimental data for the whole range. Comparisons with the NBS/NRC steam tables show deviations within 0.001 cm3/g below 200-degrees-C, reaching their maximum of 0.006 cm3/g at 250-degrees-C.