The macroscopic temperature and pressure jumps that occur at a condensate surface during a nonequilibrium phase change are calculated using a variational principle on the linearized Boltzmann equation. When evaluated for the BGK collisional model, the macroscopic jumps have values within 1% of a recent numerical calculation. Furthermore, the microscopic density and temperature jumps are estimated using an ansatz for the distribution function of molecules impinging on the surface. The jumps obtained in this way are correct to within 5% of the numerical values when evaluated for the BGK model. Also a simple procedure is described by which the jumps occuring at a surface for which the mass accommodation (condensation) coefficient σ≠1 may be calculated from those for which σ=1. In addition the connection of this kinetic theory with the thermodynamics of irreversible processes is made and the elements of the appropriate Onsager matrix are expressed in terms of the macroscopic jumps for arbitrary values of σ.

Kinetic theory of condensation and evaporation. II

During their transport to processing plants, produced hydrocarbon streams are always accompanied by water appearing as a separate phase in contact with the hydrocarbons. Dramatic temperature and pressure changes during processing can lead to condensation of water and possibly hazardous formation of ice and hydrates. Historically, methanol has been the dominating chemical agent added to prevent the formation of solid water phases. In this work, the technique of molecular dynamics simulation has been utilized to investigate and illustrate the impact of methanol as a surfactant in a water–methane system. We have found that adding 5% of methanol boosted the diffusion of methane through the interface by more than 40% compared to the reference system. The amount of methane accumulated in the aqueous phase was also significantly higher. This effect will likely also result in a significant increase in homogeneous and heterogeneous hydrate formation in these regions in the case of the methanol-stimulated system, and thus necessitate the application of classical nucleation theory. In particular, our analysis emphasised the fact that several different hydrates may form in this scenario. In case of the homogeneous hydrate formation, there will theoretically exist an infinite number of hydrate phases corresponding to concentrations spanning the range between methane's solubility and its hydrate stability limit.

Methanol as a hydrate inhibitor and hydrate activator

The relation between the non-equilibrium thermodynamics and kinetic theory of rarefied gases is discussed. The phenomenological equations of generalized non-equilibrium thermodynamics are formulated using the fundamental relations of kinetic theory. Using the approach developed, the non-equilibrium thermodynamics of a multicomponent gas mixture are formulated for the moment method and Burnett approximation and the boundary conditions including the slip and jump effects are derived for slightly rarefied gases. An application to transport processes in discontinuous systems and gas flows over solid bodies is also made.

http://iopscience.iop.org/article/10.1070/PU1998v041n04ABEH000383/pdf

Non-equilibrium thermodynamics and kinetic theory of rarefied gases

Non-equilibrium thermodynamics and kinetic theory of gas mixtures in the presence of interfaces

It is shown that the inverted temperature profile between an evaporating and a condensing surface, which is a controversial result of kinetic theory, cannot be excluded by nonequilibrium thermodynamics.

The temperature paradox in the kinetic theory of evaporation

Abstract The entropy production - (3.8.) - in the boundary between two phases of a one-component system contains two scalar force-flux pairs. The \"forces\" are the jumps of the temperature and of (essentially) the chemical potential at the interface; the \"fluxes\" are the heat and mass fluxes nor-mal to the interface. So, four phenomenological coefficients appear in the pertaining local linear constitutive laws - (4.14 and 15) - for the boundary conditions. They can in principle be de-termined by a stationary heat conduction and phase transition experiment. Only measurements of temperature jumps - (5.14 and 15) - are involved. These jumps vanish if the four coefficients vanish

https://www.degruyter.com/dg/viewarticle.fullcontentlink:pdfeventlink/$002fj$002fzna.1972.27.issue-7$002fzna-1972-0701$002fzna-1972-0701.pdf?format=INT&t:ac=j$002fzna.1972.27.issue-7$002fzna-1972-0701$002fzna-1972-0701.xml

L Waldmann

Papers

Non-Equilibrium Thermodynamics of Phase-Transitions