AN AUTOMATED HIGH-PRESSURE PVT APPARATUS FOR CONTINUOUS RECORDING OF DENSITY AND ISOTHERMAL COMPRESSIBILITY OF FLUIDS

A unique instrumentation which permits real-time automated recording o f volume or density as a function of pressure is described. The system consists of a variable volume view cell with an internal movable pist on, a piston position sensor, a motorized pressure generator, and comp uterized control and data acquisition units. The position of the pisto n and hence the internal volume of the cell is monitored in real time with the aid of a linear-variable differential transformer while the p ressure of the cell is changed in a slow, programed fashion using the automated pressure generator. The system is fully automated and can be used to generate density and compressibility information for pure flu ids and fluid mixtures over a wide range of temperatures (up to 473 K) and pressures (up to 70 MPa). The continuous recording of density mak es it possible to detect subtle changes in the state of the fluid(s) a nd offers a convenient approach for precise determination of the phase transition conditions. The capabilities of the system are demonstrate d for two pure fluids, carbon dioxide and n-pentane, at near- and supe rcritical conditions. (C) 1996 American Institute of Physics.