Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Mass transfer turbulent

Volumetric mass transfer coefficient, kLa The proportionality coefficient reflecting both molecular diffusion, turbulent mass transfer, and specific area for mass transfer. [Pg.907]

The turbulent mass transfer in the flow resulting from the interaction of the two jets is more extensive than in a single jet under the same supply conditions. [Pg.503]

In turbulent flow, the edge effect due to the shape of the support rod is quite significant as shown in Fig. 6. The data obtained with a support rod of equal radius agree with the theoretical prediction of Eq. (52). The point of transition with this geometry occurs at Re = 40000. However, the use of a larger radius support rod arbitrarily introduces an outflowing radial stream at the equator. The radial stream reduces the stability of the boundary layer, and the transition from laminar to turbulent flow occurs earlier at Re = 15000. Thus, the turbulent mass transfer data with the larger radius support rod deviate considerably from the theoretical prediction of Eq. (52) a least square fit of the data results in a 0.092 Re0 67 dependence for... [Pg.185]

Turbulent mass-transfer relations concerning forced convection are of interest for two main reasons (see Table VII, Part D) (a) because of their practical importance, since turbulence promotes increase of transfer rates and (b) they afford an indirect means of gaining insight into the mechanism... [Pg.268]

Numerous turbulent mass-transfer relationships are given in Eqs. (39)-(50), Table VII. Although the most important ones in practical applications are those for channels and tubes, several other configurations also have been investigated because of their hydrodynamic interest. Generally, it is not possible to predict mass-transfer rates quantitatively by recourse to turbulent flow theory. An exception to this is for the region of developing mass transfer, where a Leveque-type correlation between the mass-transfer coefficient and friction coefficient/can be established ... [Pg.269]

By substituting the well-known Blasius relation for the friction factor, Eq. (45) in Table VII results. Van Shaw et al. (V2) tested this relation by limiting-current measurements on short pipe sections, and found that the Re and (L/d) dependences were in accord with theory. The mass-transfer rates obtained averaged 7% lower than predicted, but in a later publication this was traced to incorrect flow rate calibration. Iribame et al. (110) showed that the Leveque relation is also valid for turbulent mass transfer in falling films, as long as the developing mass-transfer condition is fulfilled (generally expressed as L+ < 103) while Re > 103. The fundamental importance of the Leveque equation for the interpretation of microelectrode measurements is discussed at an earlier point. [Pg.269]

An equally important objective of these turbulent mass-transfer measurements was the establishment of the exact dependence of k on the Reynolds number. The well-known empirical Chilton-Colburn equation for turbulent transfer (C3) predicts that... [Pg.270]

Expressions for Fully Developed Turbulent Mass Transfer... [Pg.271]

One really may need an inherently transient LES to capture all these details. The finer the grid for such a LES, the more reliably the local transient conditions may be taken into account in reproducing this turbulent mass transfer process (while ignoring the issue of supplying the heat for the dissolution which may also depend on a proper representation of the turbulent-flow field). An additional important issue is how many particles have to be tracked for a proper representation of the transient spatial distribution of the particles over the vessel. [Pg.197]

In what follows, the preceding evaluation procedure is employed in a somewhat different mode, the main objective now being to obtain expressions for the heat or mass transfer coefficient in complex situations on the basis of information available for some simpler asymptotic cases. The order-of-magnitude procedure replaces the convective diffusion equation by an algebraic equation whose coefficients are determined from exact solutions available in simpler limiting cases [13,14]. Various cases involving free convection, forced convection, mixed convection, diffusion with reaction, convective diffusion with reaction, turbulent mass transfer with chemical reaction, and unsteady heat transfer are examined to demonstrate the usefulness of this simple approach. There are, of course, cases, such as the one treated earlier, in which the constants cannot be obtained because exact solutions are not available even for simpler limiting cases. In such cases, the procedure is still useful to correlate experimental data if the constants are determined on the basis of those data. [Pg.20]

N. Turbulent Mass Transfer with First-Order Chemical Reaction... [Pg.46]

Turbulent mass transfer near a wall can be represented by various physical models. In one such model the turbulent flow is assumed to be composed of a succession of short, steady, laminar motions along a plate. The length scale of the laminar path is denoted by x0 and the velocity of the liquid element just arrived at the wall by u0. Along each path of length x0, the motion is approximated by the quasi-steady laminar flow of a semiinfinite fluid along a plate. This implies that the hydrodynamic and diffusion boundary layers which develop in each of the paths are assumed to be smaller than the thickness of the fluid elements brought to the wall by turbulent fluctuations. Since the diffusion coefficient is small in liquids, the depth of penetration by diffusion in the liquid element is also small. Therefore one can use the first terms in the Taylor expansion of the Blasius expressions for the velocity components. The rate of mass transfer in the laminar microstructure can be obtained by solving the equation... [Pg.49]

Since the term local in the case of turbulent flow refers to a path of length xa, the local turbulent mass transfer coefficient should be defined as the average... [Pg.60]

One may note that two kinds of considerations are involved in the two treatments of turbulent mass transfer near a solid boundary. First, the local turbulent behavior is described by microlaminar motions over short path lengths, and, second, the scales of the laminar microstructure are expressed in terms of the characteristics of the turbulent motion. [Pg.61]

M. Turbulent Mass Transfer near a Liquid-Fluid Interface Based on the Turbulent Diffusivity Concept Turbulent Flow of a Liquid Film on a Vertical Wall... [Pg.81]

Two approaches can be used for the analysis of turbulent mass transfer near a liquid-fluid interface. One has the time-averaged convective diffusion equation as the starting point. For obtaining in that procedure an equation for... [Pg.81]

N. Turbulent Mass Transfer in a Stirred Vessel Rate of Absorption through the Free Surface of the Liquid... [Pg.83]

In this section we emphasize a parallelism between the Danckwerts statistical model and a deterministic representation of the turbulent mass transfer [116], The starting point was the observation that an almost... [Pg.107]

The mass-transfer rate between two fluid phases will depend on the physical properties of the two phases, the concentration difference, the interfacial area, and the degree of turbulence. Mass-transfer equipment is therefore designed to give a large area of contact between the phases and to promote turbulence in each of the two fluids. [Pg.354]

Quarmby, A. and Anand, R.K. (1969). Axisymmetric turbulent mass transfer in circular pipe tube../. Fluid Mech., 38, 433-455. [Pg.167]

In most common separation processes, the main mass transfer is across an interface between a gas and a liquid or between two liquid phases. At fluid-fluid interfaces, turbulence may persist to the interface. A simple theoretical model for turbulent mass transfer to or from a fluid-phase boundary was suggested in 1904 by Nernst, who postulated that the entire resistance to mass transfer in a given turbulent phase lies in a thin, stagnant region of that phase at the interface, called a him, hence the name film theory.2 4,5 Other, more detailed, theories for describing the mass transfer through a fluid-fluid interface exist, such as the penetration theory.1,4... [Pg.156]

This simple flow pattern becomes unstable at higher rotation speeds, and a cellular flow pattern (termed Taylor vortices) is observed. Taylor vortices provide an irregular enhancement to mass transfer. At still higher rotation speeds, the flow becomes fully turbulent. Mass-transfer studies with rotating cylinders are conducted in the turbulent flow regime because the flow provides a uniform enhancement to mass transfer. [Pg.209]

In a packed absorption column, the fluid is in turbulent motion. Mass transfer through the Aims is deflned by ky and k, which are now turbulent mass transfer coefficients. An equation similar to that for molecular diffusion can be used to describe the mass transfer. However, in this case, the concentration difference is expressed in terms of mole fractions at the interface. The molar mass transferred Na can be found from Eq. (18). [Pg.2006]

Note that the sign and magnitude of the flux of acetone is sensitive to the value of the Re number (why ) and to the choice of the turbulent mass transfer model (again, why ). Rationalize your results in terms of the results portrayed in Figure 10.8. [Pg.494]

V. S. Arpaci, (Keynote Lecture), Microscales of turbulence, mass transfer correlations, International Symposium on Turbulence, Heat and Mass Transfer, Lisbon, Portugal, 1994a. [Pg.330]


See other pages where Mass transfer turbulent is mentioned: [Pg.599]    [Pg.272]    [Pg.272]    [Pg.272]    [Pg.58]    [Pg.85]    [Pg.107]    [Pg.108]    [Pg.156]    [Pg.157]    [Pg.284]    [Pg.117]    [Pg.12]    [Pg.248]    [Pg.249]    [Pg.251]    [Pg.253]    [Pg.157]   
See also in sourсe #XX -- [ Pg.22 ]

See also in sourсe #XX -- [ Pg.717 ]




SEARCH



Mass transfer turbulence

© 2024 chempedia.info