Flow nonuniformities

The effects of flow nonuniformities, in particular, can be severe in gas systems when the ratio of bed-to-particle diameters is small in liquid systems when viscous fingering occurs as a result of large viscosity gradients in the adsorption bed when very small particles (<50 Im) are used, such as in high performance liqmd chromatography systems and in large-diameter beds. A lower bound of the axial... 

Neglecting flow nonuniformities, the contributions of molecular diffusion and turbulent mixing arising from stream sphtting and recombination around the sorbent particles can be considered additive [Langer et al., Int. ]. Heat and Mass Transfer, 21, 751 (1978)] thus, the axial dispersion coefficient is given by ... 

The effects of flow nonuniformities, in particular, can be severe in gas systems when the ratio of bed-to-particle diameters is small in liquid systems when viscous fingering occurs as a result of large... 

Influence of Flow Nonuniformity on the Mass and Heat Transfer Conditions in Cooling Towers)... 

Screens and other flow restrictions may also be used to suppress stream swirl and turbulence (Loehrke and Nagib, J. Fluids Eng., 98, 342-353 [1976]). Contraction of the channel, as in a venturi, provides further reduction in turbulence level and flow nonuniformity. 

An extended discussion of zone spreading and plate height in nonuniform separation systems is beyond the scope of the present chapter. However, later we account for flow nonuniformities due to gas compressibility in gas chromatography. More generally, the treatment developed by the author [8,16] for chromatographic columns can be expanded to describe most other zonal systems. 

A particular case of flow nonuniformity is inherent to all randomly packed tubes (Fig. 8). This is due to the fact that the catalyst pellets make only point contact with the wall, whereas they overlap and cross over one another inside the packing, thereby reducing the free volume and hence the velocity. The conditions for a spherical packing are illustrated schematically in Figure 8. The radially varying empty space distribution and velocity distribution must be taken into account in detailed reactor calculations, as well as in the determination of accurate heat transport parameters [17, 18]. This will be addressed in the next section. 

A disadvantage of the differential reactor is the inaccuracy in the determination of conversion and selectivity due to the small concentration changes. The second difficulty in the treatment of experimental data is caused by possible flow nonuniformities. Since the average residence time is short and the fluid elements moving with different axial velocities do not mix, the simplified Equation 5.30 may not be valid. This is because the reactor operates as a segregated flow reactor rather than a plug flow or ideal mixed reactor, on which Equation 5.30 is based. 

An additional and important advantage of the recycle reactor, compared to the differential packed bed reactor, is that here flow uniformity through the bed is not required, so channeling is not a problem and one layer of catalyst or even separate particles can be used in the reactor. For packed bed reactors, flow nonuniformity would inhibit the application of the plug flow model. 

Electro-osmotic Flow Nonuniformity Influence on Efficiency of Capillary Victor P. Andreev... 

Departures from the assumption of small-amplitude oscillations about a uniform, quiescent state can modify the modes of oscillation. Also, the boundary conditions influence the solutions [for example, if there were an open isobaric boundary, then p = 0 would be appropriate there, and equation (8) would be changed]. Nevertheless, the results that have been given form good first approximations for use in approaches to the analysis of acoustic instabilities. Frequencies and spatial dependences of amplitudes are less strongly influenced by flow nonuniformities that are the magnitudes of the amplitudes of the various modes. Nothing in what has been presented so far provides a basis for calculating the constants bk , and... 

If flow nonuniformities are present on both sides, the performance deterioration factor can be either larger or smaller than that for the case where flow nonuniformity is present only on one side, and there are no general guidelines about the expected trends. 

The pan is considered to be much deeper (into the paper) than the liquid height in the pan, h. Moreover, the pan itself is much longer than it is wide, so llh > 1, where / is the pan length. Under these conditions, any flow nonuniformities at the side walls are small and the flow is essentially two-dimensional. Since h l, the flow is nearly lateral, but, as we shall show, the liquid height... 

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