Wärmeübertragung in Gaswirbelschichten

Wicke, E.; Fetting, F.

doi:10.1002/cite.330260602

Cited by 63 publications

(15 citation statements)

References 9 publications

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“…From the data published in literature [ 5 ] , the significance of the dimensionless excess gas velocity is evident also for B powders. Fluidization of sand particles (dp = 315 pm) in air or hydrogen gave at maximum observed heat transfer 18.1 x…”

Section: Heat Transfer With B Powdersmentioning

confidence: 89%

Heat transfer in gas fluidized beds. Part 2: Dependence of heat transfer on gas velocity

Molerus

Mattmann

1992

Chem Eng & Technol

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Part 1 of this report investigated the effects of system properties on heat transfer between heating or cooling surfaces and bubbling fluidized beds. This investigation produced six correlations, which define the respective maximum heat transfer. The present contribution shows that the heat transfer depends on superficial gas velocity, with the relationship expressed in terms of a dimensionless excess gas velocity which defines the ratio of effective thermal conductivity by particle mixing to that of the fluidizing agent. Simple procedures for a reliable prediction of heat transfer in bubbling fluidized beds are presented.

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Section: Heat Transfer With B Powdersmentioning

confidence: 89%

Heat transfer in gas fluidized beds. Part 2: Dependence of heat transfer on gas velocity

Molerus

Mattmann

1992

Chem Eng & Technol

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“…The maximum values, with respect to the gas velocity, of heat transfer coefficients between a surface and the fluidized bed vary, in general, inversely as the particle size (74, 25,26).…”

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confidence: 99%

Effect of Interparticle Adhesive Forces on Fluidization of Fine Particles

Baerns¹

1966

Ind. Eng. Chem. Fund.

103

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comparable with the lov~ rates of shear used in the present work, the viscosity observed by them has been calculated to be 150 cs.This calculation is, however, only approximate, as bed density had to be assumed and the air rate was not directly ascertainable. Results obtained with the rotational viscometer used by them are roughly comparable with those here described obtained with the oscillating viscometer.There is some evidence of Newtonian behavior of the bed under the low shear stress involved in these measurements. The torsional viscometer correlation ( 2 ) is a unique function of several system variables, such as immersed body diameter and period of oscillation. When one of the system variables was altered, such as bob diameter or period, a different portion of the viscometer correlation curve became relevant. Calculations based on this different portion invariably led to substan tially the same viscosity value, whereas the mean rate of shear had been perceptibly altered, thus giving indirect evidence that the observed viscosity seems to be independent of the rate of shear.Further evidence is that, as nearly as could be ascertained in these experiments, the logarithmic rate of decay of amplitude was independent of the amplitude, as it is for a Neittonian fluid. The data of Schugerl et al. (79) for their rotational viscometei and for slow rates of immersed body rotation, also indicated an independence between viscosity and rate of shear.The theoretical predictions of Trawinski (27) are not confirmed by the results here described, in that bed viscosity did not decrease lvith particle size. Trawinski (22) also predicted a minimum viscosity a t such proportion of fines as isould coat a large particle with a "lubricating" layer of small ones. KO such minimum was observed in the present nork. literature Cited (1) Aird, R. M., B. E. (Hons) (Chem) thesis, Canterbury Universitv CollePe. The feasibility of gaseous fluidization of particles in the size range of less than 50 microns was investigated, The ratio of the incipient fluidization velocity, calculated by a conventional relationship without accounting for interparticle forces, to the incipient fluidization velocity, determined by pressure drop and heat transfer measurements, was used as an index, FI, describing the fluidizability of a particulate material. The results indicate that FI is closely related to the interparticie adhesive force. The limitations of the feasibility of fluidization depend on the ratio of the weight of a particle to the sum of its weight and adhesive force; no fluidization could be obtained when this ratio was less than 1 O-3. FLUIDIZATIOS of fine particles is becoming of interest in vari-ous chemical processes such as the fluorination of uranium compounds-e.g., Us08, U02F2, UF,-the preparation of uranium monocarbide, and the coating of reactor fuel particles. Fine particles are in general difficult to fluidize. This difficulty is related to interparticle forces (76, 77) which are greater than those transmitted to the particles by the ...

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Section: Extremely Low Heat Transfer Coefficient: Styropormentioning

confidence: 91%