Application of Irreversible Thermodynamics to Diffusion in Solids with Internal Surfaces

Two types of additional variables were included in the set of state variables and were used for a thermodynamic description of diffusion in an ordinary thermodynamic system. Vacancies are included in the mass balance. Internal surfaces are massless but are characterized by some energy, which is included in the energy balance of the thermodynamic system. Fluxes of components, vacancies, and surfaces were expressed via two groups of thermodynamic constitutive equations of with cross effects. The first group follows from the Gibbs equation. These are state equations in a differential form. The second group relates generalized thermodynamic fluxes to generalized thermodynamic forces. It was shown for a binary system that only three of six transfer coefficients are independent even if the mass transfer mechanism caused by the stress gradient is taken into account.

Heat and mass transfer modeling during laminar condensation of non-cryogenic downward fluids flow in a small vertical tube

The purpose of this paper is to investigate mass and heat transfer in the process of film condensation of vapor-air mixture for non-cryogenic fluids flow in a small vertical tube. A two-phase mathematical model is developed to model the mixture and liquid film. The governing equations for mixture and liquid-film have been resolved using a numerical method. Furthermore, this phenomenon analyzed is linked to a steady-state. Therefore, the development of numerical codes allows us to investigate the effect of implicated parameters on this phenomenon. Ethanol and methanol as non-cryogenic typical working fluids are realized for a good understanding of the heat and mass transfer mechanism during condensation. In this way, several effects of influencing parameters were examined. The predicted results showed a good agreement with experimental data.