Thermo-Mechanical Exergy of a Substance Below Environmental Pressure

In this work, we demonstrate why classical thermo-mechanical exergy functions are incorrect below the environmental reference pressure, since they result in too small or even negative values. We present new derivations for thermo-mechanical exergy for fluids at any temperature or pressure above or below the environmental reference temperature and pressure. We then present new pressure–enthalpy–exergy diagrams of real chemicals to visually demonstrate the results.