Non-equilibrium Thermodynamics for Evaporation and Condensation
Non-equilibrium thermodynamics gives dynamic boundary conditions for transport of heat and mass into and through surfaces far from reversible conditions. Conversions between thermal, mechanical and chemical energy are described through force–flux relations. Among the transfer coefficients, the coupling coefficient is large at interfaces, unlike in the homogeneous phase. The magnitude and sign of the coupling coefficient are determined by the enthalpy of the phase transformation. This has a bearing on the modelling of phase transitions, as simple laws of transport become insufficient, even wrong. The coefficients for evaporation and condensation are given and compared to results from kinetic theory. Transfer coefficients from experiments, molecular dynamics simulations and from the use of the van der Waals square gradient theory, are reviewed. The need for more work along these lines is pointed out. A short discussion is also given about contact lines.