Oxygen inhomogeneity

It has been shown that various small scale models consisting of idealized reactor types can be used to simulate large scale fermentation processes, with respect to dissolved oxygen inhomogeneities. The reaction kinetic expressions, material balances on substrates, and products have to be formulated and solved in the context of the combined model network. The choice of the model configuration depends on (1) the system that has to be simulated, (2) knowledge of the hydrodynamics of the system, and (3) the equipment available and financial resources. 

Pits occur as small areas of localized corrosion and vary in size, frequency of occurrence, and depth. Rapid penetration of the metal may occur, leading to metal perforation. Pits are often initiated because of inhomogeneity of the metal surface, deposits on the surface, or breaks in a passive film. The intensity of attack is related to the ratio of cathode area to anode ai ea (pit site), as well as the effect of the environment. Halide ions such as chlorides often stimulate pitting corrosion. Once a pit starts, a concentration-cell is developed since the base of the pit is less accessible to oxygen. 

Daw et al. [632] made a microscopic and crystallographic study of talc dehydroxylation. Nucleation, to yield enstatite, occurs inhomogeneously within the particles, perhaps at dislocations. Later, this product is topo-tactically orientated with respect to the reactant lattice, though with extensive faulting on the (010) plane owing to misfit, in addition to the attempt to preserve the oxygen lattice. In an isothermal study (1100— 1160 K) of the same reaction, Ward [633] found first-order obedience and the value of E determined (422 kJ mole-1) is close to that estimated for... 

The power law (2.1) can also be deduced from assumptions concerning the energy inhomogeneity on the surface of adsorbent [27, 54, 55]. Namely, assuming the availability of exponential distribution with respect to the heat of adsorption, in other words, assuming the validity of the Freindlich isotherm for adsorption of oxygen on oxides, Clifford... 

Another typical example of inhomogeneity in rheometry is the oxidation of a polymer in a rotational rheometer in which a disk-shaped sample is held between metal fixtures. The oxygen enters the sample through the free surface (at the outer diameter) and diffuses radially inwards. The result is a radial gradient in properties which changes with time. If the reaction with oxygen results in... 

The results from Fig. 14.1 show the developing turbulent flame zone. The nonsymmetries of the reaction rate field are due to inhomogeneity of the polydis-persed mixture, i.e., nonsymmetrical distribution of model particles and their velocities. The reaction front is under formation oxygen and partially the volatiles in the center are burnt out, but the reaction front is not sphere-shaped yet. The nonuniformity of the model particles distribution was induced initially due to the stochastic modeling of the particulate phase. 

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