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The boiling temperature, referred to as the saturation temperature is well known for an equilibrium process. It is defined, in a similar way to any thermodynamic state, by two independent thermodynamic properties, e.g. pressure and specific vapor. The collection of these points is referred to as the binodal.
Van-Der-Waals (VDW), however, "disagrees". Nucleation, according to his cubic equation of state, will occur at the spinodal, which is the collection of the thermodynamic states that are the limit of thermodynamic stability. The region that is bounded between the binodal and the spinodal is referred to as the metastable region.
We know that nucleation can occur at any point between the binodal and the spinodal. Furthermore, it is known that for a real liquid (not lacking of some impurities) the penetration depth into the metastable region depends on the heating rate. Moreover, the kinetic theory points out that for an infinite penetration rate, the thermodynamic limit of stability (the spinodal) will be reached.
What, if then, is the nucleation temperature as a function of the heating rate?
We propose a new simple universal correlation that predicts the onset of nucleation temperature following a rapid isobaric heating process. The correlation predicts the nucleation temperature, as a function of the heating rate, with knowledge of only the saturation and homogeneous nucleation conditions for various liquid types. The predictions are validated for different fluids: water, methanol, ethanol (polar) and heptane and toluene (non-polar).
