PressureVolumeTemperature

Pressure-volume-temperature (PVT) relationships describe how the pressure, volume, and temperature of a substance relate to one another for a given amount of material. PVT data are a foundational component of thermophysical property databases and are used to characterize fluids in science and engineering. They apply to gases, liquids, and mixtures and underpin predictions of phase behavior, density, and flow performance in industrial equipment.

In the simplest case, ideal gas behavior obeys P V = n R T, where the compressibility factor Z = P V /(n R T) is approximately 1. Real fluids exhibit deviations from this idealization, especially near phase transitions or at high pressures. To model these deviations, equations of state (EOS) such as van der Waals, Redlich-Kwong, Soave-Redlich-Kwong, and Peng-Robinson are employed. Cubic EOS are particularly common for generating PVT data and phase envelopes for mixtures, enabling calculation of properties across a range of pressures, volumes, and temperatures.

PVT data are obtained experimentally using specialized equipment such as PVT cells, dilatometers, or vibrating-tube densitometers, and can also be derived from molecular simulation or indirect measurements. The resulting information yields properties including density, molar volume, and the compressibility factor, and supports calculations of phase equilibria, enthalpies, and transport properties when combined with appropriate correlations or models.

Applications of PVT analysis span chemical engineering and petroleum engineering, informing reservoir simulations, process design, optimization, and the interpretation of phase behavior for pure components and complex mixtures.