Momentum and mass transfer by eddy diffusioin in a wetted‐wall channel

Dhanak, A. M.

doi:10.1002/aic.690040213

Cited by 8 publications

(3 citation statements)

References 7 publications

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“…The theory of Mothes and Loffler (1988), which divides the cyclone into three distinct regions (a fourth region is possible if reentrainment is occurring) coupled with the concept of a finite diffusivity provides the best fit with the experimental data. The fitted particle turbulent diffusivities Dp are in the range obtained experimentally by Leonard et al (1982), Self et al (1987) and Erlich and Melcher (1987) for turbulent flows, and generally much larger than predicted from available theories or empirical formulae (Taylor, 1954;Dhanak, 1958;Becker et al, 1966). Order of magnitude agreement for the fitted diffusivity is obtained with the experimental grade collection in a standard type sampling cyclone collecting a fine alumina dust (Salcedo, 1981).…”

Section: Discussionsupporting

confidence: 72%

“…The diffusivities are roughly one order of magnitude larger for the Mothes and Loffler model, and for cyclones B and C they are in the range obtained experimentally for turbulent flows (Leonard et al, 1982;Self et al, 1987;Erlich and Melcher, 1987). However, if the effective diffusivity is estimated from Equation (12) or from empirical relations developed for turbulent flows (see for example Dhanak, 1958;Becker et al, 1966), then much smaller values for Dp (between lop5 and m2/s) are obtained. The discrepancy between the fitted turbulent diffusivities as compared to those obtained from empirical relations developed for turbulent flows may also be due to non-uniformity particle distribution at the cyclone inlets or to axially non-uniform radial gas velocity at the vortex finder.…”

Section: Resultsmentioning

confidence: 99%

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Collection efficiencies and particle size distributions from sampling cyclones — comparison of recent theories with experimental data

Salcedo

1993

Can J Chem Eng

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The grade collection efficiencies and particle size distributions from Stairmand-type cyclones are compared with predictions from four theories, viz. the models of Leith and Licht (1972), Dietz (1981) Mothes and Loffler (1988) and Li and Wang (1989). It is shown that the theory of Mothes and Loffler, which recogizes different flow regions within a cyclone, coupled with a realistic estimate of the particles turbulent diffusivity, is capable of providing good estimates of both the grade-efficiency curves and particle size distributions of the cyclone catch and/or outlet dusts.The lack of adequate theories or empirical formulae to estimate the effective turbulent diffusivity under cyclone flow seems the major factor hindering the use of the Mothes and Loffler theory for predictive purposes. High loadings and agglomeration of fines, if present, are responsible for strong departures from theoretical predictions. Les efficacitks de collection des qualitks et les distributions de taille des particules obtenues de cyclones d'dchantillonnage de type Stairmand sont comparkes aux pridictions de quatre modbles thkoriques, soit les modbles de Leith et Licht (1972), de Dietz (1981), de Mothes et Loffler (1988) et de Li et Wang (1989). On montre que la thdorie de Mothes et Loffler, qui considhe diffkrentes rigions d'kcoulement B I'intkrieur d'un cyclone, est capable, lorsqu'elle est couplke a une estimation rkaliste de la diffusivitk turbulente des particules, de fournir de bonnes estimations des courbes d'efficacitk des qualit& et des distributions de taille des particules des poussibres au collecteur ou B la sortie du cyclone. L'absence de thkories ou de formules empiriques addquates pour estimer la diffusivitk turbulente rdelle dans des conditions d'kcoulement de cyclone semble le facteur principal qui empkche l'utilisation de la thkorie de Mothes et Loffler a des fins de prkdiction. Les charges Clevkes de fines et leur agglomkration, lorsqu'il y en a, sont responsables des importants kcarts par rapport aux prdictions thkoriques.yclone samplers are inexpensive and easy to build dust C samplers (Stairmand, 1951). They can be used for the collection of large quantities of dust and can be operated on-line with high-temperature, high-pressure applications (Mothes and Loffler, 1988;Li and Wang, 1989). Measurements of the particle size distributions of both the cyclone inlet and cyclone catch together with the over-all gravimetric efficiency provide a means of obtaining the grade-efficiency curve and the particle size distribution of the cyclone exit dust. Sampling cyclones may also be employed to obtain the dust catch or exit distributions and the over-all gravimetric efficiency from a known inlet distribution and gradeefficiency curve. It would under all circumstances be of great advantage to be able to predict accurately both the over-all gravimetric efficiency and the grade-efficiencies from considerations of cyclone geometry, flow conditions and information on particle size distributions (inlet, catch or outlet).The theory of...

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Section: Discussionsupporting

confidence: 72%

Section: Resultsmentioning

confidence: 99%

Collection efficiencies and particle size distributions from sampling cyclones — comparison of recent theories with experimental data

Salcedo

1993

Can J Chem Eng

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“…Dhanak (9) DorWeiler' (10) illustrated the interaction between molecular ~nd ed.dy dif:tusi vi ties by extending the mass transfer data for packed beds to low floW rates including the "transition" and "laminar" regions.…”

Section: ··mentioning

confidence: 99%