Non-equilibrium evaporation and condensation : modeled with irreversible thermodynamics, kinetic theory, and statistical rate theory

• Main Author: Bond, Maurice.
• Other Authors: Struchtrup, Henning
• Published: 2008
• Subjects: Evaporation; Condensation
• Online Access: http://hdl.handle.net/1828/511

The purpose of this work is to demonstrate the usability of irreversible thermodynamics and kinetic theory in describing slow steady state evaporation and condensation, analyze the statistical rate theory (SRT) approach, and investigate the physical phenomena involved. Recently large interface temperature jumps have been observed during steady state evaporation and condensation experiments; the vapor interface temperature was greater than the liquid interface temperature for condensation and evaporation. To predict the temperature jump, the SRT mass flux was introduced as an alternative to the established approaches of irreversible thermodynamics and kinetic theory of gases. Simple one dimensional planar and spherical models were developed for slow evaporation and condensation based on the experiments. We considered pure liquid water evaporation and condensation to, and from its own vapor. Expressions for the mass and energy fluxes across the interface were found using irreversible thermodynamics, kinetic theory, and SRT. The SRT theory does not have an energy flux expression, as a substitute we use the irreversible thermodynamics energy flux in the SRT model. The equations were then solved to yield the mass and energy fluxes, and the liquid and vapor temperature profiles. We find the interface temperature jump is dependant on the energy flux expression. The irreversible thermodynamics energy flux closely predicts the measured temperature jump and direction. Kinetic theory models do not predict the jump, however with incorporation of a velocity dependant condensation coefficient, kinetic theory can predict the correct temperature jump direction, and vapor interface temperature. All the models predict mass fluxes that agree with the measured data. We suggest the temperature jump direction is established based on the direction of the vapor conductive energy flux, and not the direction of the mass flux (condensation or evaporation). We conclude that irreversible thermodynamics, kinetic theoiy, and SRT can all be used to model steady state evaporation and condensation.