Non-equilibrium Conditions and Rate Processes

Phase non-equilibrium. If a chemical potential gradient exists between two adjacent and homogenous phases, the system is not in local phase equilibrium and a rate-limited mass transfer phenomenon occurs. A momentum balance of specie i results in the following expression for the driving force exerted on i as a function on the friction 

A fully description of the non-equilibrium mass transfer phenomenon embraces simultaneously a Maxwell-Stefan diffusion model and a flow model. The most commonly used approach is the film model, which is addressed in more detail in the explanatory note 2.1. 

According to this definition, Damkohler number gives the ratio of the characteristic process time to the characteristic reaction time (Doherty and Malone, 2001) and captures effectively the major dependence of conversion, production rate and product purities on the feed flowrate, catalyst level and holdup (Chen et al., 2002). For an open 

Film model is undoubtedly the most widespread approach for the rate-based mass and heat transfer through an interface (Wesselingh and Krishna, 2000). It effectively combines species diffusion and fluid flows and is based on the assumption that the resistance to mass and heat transfer is exclusively concentrated in a thin film where steady state diffusion and mass and heat convection take place (figure 2.5). 

the interfacial mass and heat transfer fluxes are composed of a laminar, steady state diffusion term in the stagnant film and a convection term from the complete turbulent bulk phase (Taylor and Krishna, 1993), 

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