Peclet number mass transfer

Peclet number (mass transfer) Pe Re Sc = VL D Dimensionless independent mass transfer coefficient (ratio of bulk mass transfer to diffusive mass transfer) Mass transfer... 

Naturally, there are two more Peclet numbers defined for the transverse direction dispersions. In these ranges of Reynolds number, the Peclet number for transverse mass transfer is 11, but the Peclet number for transverse heat transfer is not well agreed upon (121, 122). None of these dispersions numbers is known in the metal screen bed. A special problem is created in the monolith where transverse dispersion of mass must be zero, and the parallel dispersion of mass can be estimated by the Taylor axial dispersion theory (123). The dispersion of heat would depend principally on the properties of the monolith substrate. Often, these Peclet numbers for individual pellets are replaced by the Bodenstein numbers for the entire bed... 

An attempt has been made by Johnson and co-workers to relate such theoretical results with experimental data for the absorption of a single carbon dioxide bubble into aqueous solutions of monoethanolamine, determined under forced convection conditions over a Reynolds number range from 30 to 220. The numerical results were found to be much higher than the measured values for noncirculating bubbles. The numerical solutions indicate that the mass-transfer rate should be independent of Peclet number, whereas the experimentally measured rates increase gradually with increasing Peclet number. The discrepancy is attributed to the experimental technique, where-... 

GP 9] [R 16[ The extent of external transport limits was made in an approximate manner as for the internal transport limits (see above), as literature data on heat and mass transfer coefficients at low Peclet numbers are lacking [78]. Using a Pick s law analysis, negligible concentration differences from the bulk to the catalyst sur-... 

Study the effect of varying mass transfer and heat transfer diffusivities (D and X, respectively) and hence Peclet numbers (Pi and P2) on the resulting dimensionless concentration and temperature reactor profiles. 

H. Martin 1978, (Low Peclet number particle-to-fluid heat and mass transfer in packed beds), Chem. Eng. Sci. 33, 913-919. 

On an intermediate scale, smaller than the workpiece, but larger than the features, is a regime in the range of tens to hundreds of micrometers that is influenced by convection. This is the same size range in which convectively controlled fine structure is observed in pattern formation studies. In this regime, Debecker et al. [139] treated mass-transfer limited deposition on a set of lines in the presence of flow. They defined a Peclet number based on the line width L, the flow velocity U0 and the distance B between electrodes. 

Chemical reaction coefficient, 25 281,283, 290 combinations of, 25 293t effect on critical value of mass transfer Peclet number, 25 284t Chemical reaction engineering (CRE), 22 330... 

Mass transfer Peclet number (PeMT), 25 270, 279, 280, 281, 283, 285, 311, 316. See also Peclet numbers (Pe) critical value of, 25 283-285 effect on dimensionless reactant molar densities, 25 289t, 294-295 particle-based, 25 291 Mass-transfer rate, in liquid-bquid extraction, 10 751... 

Particle-based mass transfer Peclet number, 25 294. See also Peclet numbers (Pe)... 

Pebax, commercial block copolymer, 7 648t Pebble mills, 25 64 Pebble quicklime, 15 28 Peclet numbers (Pe), 2 63 10 763 22 746 25 686t, 687t 25 279. See also Mass transfer Peclet number (PeMT) axial dispersion in bubble tray absorbers, 2 89... 

The convective diffusion theory was developed by V.G. Levich to solve specific problems in electrochemistry encountered with the rotating disc electrode. Later, he applied the classical concept of the boundary layer to a variety of practical tasks and challenges, such as particle-liquid hydrodynamics and liquid-gas interfacial problems. The conceptual transfer of the hydrodynamic boundary layer is applicable to the hydrodynamics of dissolving particles if the Peclet number (Pe) is greater than unity (Pe > 1) (9). The dimensionless Peclet number describes the relationship between convection and diffusion-driven mass transfer ... 

D represents the diffusion coefficient. For example, low Peclet numbers indicate that convection contributes less to the total mass transfer and the latter is mainly driven by diffusion. In... 

All of these solutions fail for Pe = 0(1), so Davis and his colleagues (Zhang and Davis, 1987 Taflin and Davis, 1987) performed evaporative mass transfer experiments over the Peclet number range 0.01 < Pe < 4. using electrodynamically levitated droplets of hexadecane in flowing Nj and He and dodecanol in Nj. 

In equation 17, Pes (Pes = VqL/D) is the Peclet number for mass transfer, as defined in Table II, and scales the importance of convective solute transport by the velocity in the bulk (scaled by V0) to diffusion. The dimensionless solute balance at the melt-crystal interface is the generalization of equation 3 for a steadily solidifying interface dD v... 

The Peclet numbers are useful for estimating the relative contributions of convection and diffusion to mass and heat transfer. If Pe is large (>10), convection dominates, and a plug-flow model may be appropriate for simple reactor computations. When Pe is small (<<1), diffusion dominates, and the system behaves like a well-stirred reactor. Thus, Pe may be used to estimate whether downstream impurities can diffuse into the deposition zone. 

The conditions presented above have been formulated for the case that the values of the Peclet numbers for heat and mass dispersion in a bed are indentical. However, recent experimental research on axial heat dispersion in packed beds has indicated that the values of the Peclet number for heat transfer may be different from those for mass transfer (48). Fortunately, the aforementioned conditions are still valid, however, the critical values of B and Pe as well as the bounds Dan,in and Da x are dependent on the ratio q = PeH/PeM. From the theoretical results may be inferred that for highly exothermic reactions multiple steady states may... 

Peclet number for heat and mass transfer, respectively... 

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