Internal diffusion overview

J0.2.2 Step 2 Overview Internal Diffusion 660 /0,2. Adsorption Isotherms 661... 

Most of these long-term emissions are due to internal diffusion within the building material itself. In such cases, with solid and dried materials, SER, is not affected to any great extent by the air velocity over the material surface. An overview of parameters affecting SER of VOCs from building products is given by Wolkoff (1995) and experimentally evaluated (Wolkoff, 1996b). 

The influence of interfaeial potentials (diffusion or liquid junction potentials) established at the boundary between two different electrolyte solutions (based on e.g. aqueous and nonaqueous solvents) has been investigated frequently, for a thorough overview see Jakuszewski and Woszezak [68Jak2]. Concerning the usage of absolute and international Volt see preceding chapter. 

In order to take into account the effect of both mechanisms, more complicated models have been proposed [1,2,11,43-45]. Overviews have been given by Uhlhorn et al. [21] and more recently by Veldsink [46]. The models differ in the way the different mechanisms cire combined and which coupling terms are taken into account. The most important coupling effects are the occurrence of drag effects in mixtures and of momentum transfer between different species. Drag effects on molecular species a and b occur in isobaric binary mixtures a-b due to differences in molecular velocities between species a and b, which induce internal pressure differences causing a net flow of the mixture which has to be superimposed on the diffusive fluxes of a and b. 

Overview In many industrial reactions, the overall rate of reaction is limited by the rate of mass transfer of reactants between the bulk fluid and the catalytic surface. By mas,s transfer, we mean any proces.s in which diffusion plays a role. In the rate laws and catalytic reaction steps described in Chapter 10 (diffusion, adsorption, surface reaction, desorption, and diffusion), we neglected the diffusion steps by saying we were operating under conditions where these steps are fast when compared to the other steps and thus could be neglected. We now examine the assumption that diffusion can be neglected. In this chapter we consider the external resistance to diffusion, and in the next chapter we consider internal resistance to diffusion. 

Foster, S.S.D. and Candela, L. (2008) Diffuse groundwater quality impacts from agricultural land-use management and policy implications of scientific realities, In Quevauviller, P. (ed.) Groundwater Science and Policy an International Overview, RSC Publishing, Cambridge, UK, pp. 454-470. 

In support of the discussion below, we shall be forced to use ceitain geometric considerations. Figure 2.18 offers an overview of the internal make-up of an electrolyzer. Each electrode is taken to comprise a diffusive zone and a reaction... 

---