A non-equilibrium phenomenological theory of the mass and heat transfer in physical and chemical interactions: Part I — application to NH 3/H 2O and other working systems

Abstract

The paper presents an original non-equilibrium phenomenological theory of mass and heat transfer. The theory is particularized to a few case studies including physical binary gas–liquid interactions in non-ideal mixtures (e.g., working system NH 3/H 2O), pure components (NH 3, H 2O), as well as an independent chemical interaction (ammonia synthesis). All applications emphasize an important feature of the mass and heat coupled currents, that is the ideal point approaching (i.p.a.) effect, not mentioned so far in the specialized literature. The i.p.a. effect consists of a continuous increase of the mass and heat currents of an interaction evolving towards an ideal point, by several percentages (pure component case) to several hundreds of times (working pairs case), as compared to the states which are far from the same ideal point. On the contrary, the forces of systems with non-coupled mass and heat currents tend to zero when evolve to equilibrium. The paper raises the problem of the ammonia bubble absorption, not satisfactorily explained by the ‘two films’ theory. The existence of the i.p.a. effect satisfactorily explains it from a qualitative point of view. This explanation throws a new light on the absorption phenomenon encountered by the working pairs used in the thermal absorption technology: (i) absorption process is not a surface phenomenon, as it is usually considered and (ii) the actual estimation of the interface mass transfer by analogy with heat transfer is improper. The non-equilibrium approach, outlined in this paper, is not contradictory to the classic equilibrium phenomenological theory. On the contrary, it may be an equivalent alternative or it may be combined with the classic approach in order to assess mass and heat transfer processes. Its main investigation tool, the natural thermodynamical force, has specific important features in the neighbourhood of an ideal point.