Hydrodynamic interactions experimental tests

FCC catalyst testing prior to use in commercial reactors is essential for assuring acceptable performance. Purely correlative relations for ranking catalysts based on laboratory tests, however, can be erroneous because of the complex interaction of the hydrodynamics in the test equipment with the cracking kinetics. This paper shows how the catalyst activity, coke-conversion selectivity and other product selectivities can be translated from transient laboratory tests to steady state risers. Mathematical models are described which allow this translation from FFB and MAT tests. The model predictions are in good agreement with experimental data on identical catalysts run in the FFB, MAT and a laboratory riser. 

The estimation of f from Stokes law when the bead is similar in size to a solvent molecule represents a dubious application of a classical equation derived for a continuous medium to a molecular phenomenon. The value used for f above could be considerably in error. Hence the real test of whether or not it is justifiable to neglect the second term in Eq. (19) is to be sought in experiment. It should be remarked also that the Kirkwood-Riseman theory, including their theory of viscosity to be discussed below, has been developed on the assumption that the hydrodynamics of the molecule, like its thermodynamic interactions, are equivalent to those of a cloud distribution of independent beads. A better approximation to the actual molecule would consist of a cylinder of roughly uniform cross section bent irregularly into a random, tortuous configuration. The accuracy with which the cloud model represents the behavior of the real polymer chain can be decided at present only from analysis of experimental data. 

Over the past two decades several devices have been developed to measure and characterize the adhesive interaction of cells with biomaterials, particles, and other cells. These devices share the common experimental strategy that nonadherent spherical cells are allowed to establish adhesive contacts to the test material under quiescent conditions and then are subjected to a weU-defined distractive force. From the examination of large numbers of cells over a range of distractive forces, a probability distribution for cell adhesion as a function of distractive force can be constructed (Figure 34.3). From this distribution, an adhesion characteristic (e.g., T50, the shear stress necessary to detach 50% of the cells [47,86-88] maybe determined. The primary differences between the various devices for measuring cell adhesion is the type of distractive force that is applied (e.g., membrane tension, buoyancy, and hydrodynamic shear stress) and the direction of the force relative to the plane of cell/surface contacts. 

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