Wicke-Kallenbach apparatus

Two different types of dynamic test have been devised to exploit this possibility. The first and more easily interpretable, used by Gibilaro et al [62] and by Dogu and Smith [63], employs a cell geometrically similar to the Wicke-Kallenbach apparatus, with a flow of carrier gas past each face of the porous septum. A sharp pulse of tracer is injected into the carrier stream on one side, and the response of the gas stream composition on the other side is then monitored as a function of time. Interpretation is based on the first two moments of the measured response curve, and Gibilaro et al refer explicitly to a model of the medium with a blmodal pore... 

FIGURE 5.2. Schematic diagram showing essential features of the Wicke-Kallenbach apparatus for measuring intraparticle diffusivities. 

However,experiments can be carried out in such a way that intraparticle convective transport is not important.This is the case in the dynamic Wicke-Kallenbach apparatus used by different authors (Dogu and Smith [12],Furusawa et al.[l3]) and shown in Figure 2. 

Care has to be taken in designing the equipment to ensure that boundary layer effects are not present at the ends of the porous plug and that the pressure gradient across the plug is zero. Typical experimental investigations in which the Wicke-Kallenbach apparatus was used are described in the literature [34-39]. 

In connection with their work on gas-solid reactions Hills and coworkers [48] and Evans [3] have described novel techniques based on the Wicke-Kallenbach apparatus. The former used hollow spheres instead of the conventional diffusion cell the latter followed the quasi-steady state diffusion in a Wicke-Kallenbach type diffusion cell (but with gas entrance and exit lines closed) by observation of the movement of a mercury plug in a horizontal glass tube connected across the cell. 

FIG. 6.7. Schematic diagram of the Wicke-Kallenbach difTusion apparatus or diffusion bridge. 

The classical method of measuring intraparticle or macropore diffusivities is due to Wicke and Kallenbach. The apparatus is shown schematically in Figure 5.2. Knowing the thickness of the pellet and the concentrations and... 

Experimental determination of the effective diffusivity De is usually carried out in an apparatus, shown in Figure 14.2, known as a Wicke and Kallenbach chamber (1941). The chamber is operated at steady state and nearly constant pressure as is usually the case in reactors. Rewriting the definition of Eq. 14.1 for the flux, one has ... 

The diffusion bridge for porous solids was first developed by Wicke and Kallenbach [32] and later improved by Weisz [33]. A diagram of a typical apparatus is shown in Fig. 6.7. Thermal conductivity cells have usually been used as the concentration detector although any of the detectors (flame ionization, etc.) described earlier in this chapter could also be employed. 

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