GasLiquid

Gas-liquid refers to systems and processes in which gaseous and liquid phases of a substance or mixture co-exist or convert into one another. This concept is central to thermodynamics, phase behavior, and many chemical-engineering applications. In a gas-liquid system, at a given temperature and pressure the liquid and vapor phases are in equilibrium, so their chemical potentials are equal. The two-phase region is often depicted on a vapor-liquid equilibrium diagram, bounded by bubble-point and dew-point curves.

When heat is added to a liquid at a fixed pressure, vapor pressure increases and the liquid boils at the bubble point. Conversely, cooling a vapor at a fixed pressure leads to condensation at the dew point. For pure substances, the gas and liquid phases become indistinguishable at the critical point, where the liquid-gas density difference vanishes. For mixtures, ideal behavior is rarely sufficient; activity coefficients and equations of state are used to model deviation from ideality, informing vapor-liquid equilibrium data and flash calculations.

Applications of gas-liquid concepts are widespread. They include distillation and flash separation in petrochemicals, gas absorption and stripping, natural gas processing, and carbon capture. In multiphase flow, gas-liquid mixtures exhibit regimes such as bubbly, slug, and churn flow, which affect transport and equipment design. Measurement of VLE data, detection of dew and bubble points, and computational modeling with equations of state are essential for designing efficient and safe processes involving gas-liquid interfaces.