Abstract
Measurements are made on the heat-transfer coefficients between particles and fluid in the aggregative fluidized bed. In order to evaluate the heat-transfer coefficients, a proposed model takes into account of the variation of the particles-temperature and the fluid-temperature distributions throughout the bed is developped on the basis of an experimental investigation of the fluidizing behavior. The heat-transfer coefficients obtained by conforming the outlet-air temperature profile to be predicted with the one measured are found to be varied significantly depending on the static bed height, as well as particle diameter and fluid velocity.
Zusammenfassung
Wärmeübertragungskoeffizienten zwischen Teilchen und Fluid im Fließbett wurden gemessen. Das benutzte Rechenmodell berücksichtigte die Änderung der Teilchentemperatur und der Fluidtemperaturverteilung im Bett, wie sie aus den Versuchen ermittelt wurden. Die Wärmeübergangskoeffizienten, die durch Anpassung der Austrittstemperaturverteilung an die gemessenen Werte erhalten wurden, ändern sich stark mit der statischen Betthöhe, ebenso mit dem Teilchendurchmesser und der Fluidgeschwindigkeit.
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Abbreviations
- a:
-
surface area of particles per unit volume of bed
- Cp:
-
specific heat
- d:
-
diameter
- g:
-
gravitational acceleration
- hp :
-
heat-transfer coefficient between particles and fluid
- I0 :
-
modified Bessel function of the first kind of zero order
- L:
-
bed height at fluidization
- Lmf :
-
bed height at minimum fluidization
- Ls :
-
static bed height
- n:
-
natural integer
- Nup :
-
Nusselt number, hpdp /λf.
- ΔP:
-
pressure difference between static pressure in bed and atmospheric pressure
- Rep :
-
Reynolds number, Ufdp /νf.
- t:
-
time
- T:
-
temperature
- Tfi :
-
inlet-fluid temperature
- Tfo :
-
outlet-fluid temperature
- Tfoin :
-
initial outlet-fluid temperature
- Tpin :
-
initial particle temperature
- Tps :
-
particle-surface temperature
- Ub :
-
rise velocity of a bubble
- uf :
-
interstitial fluid velocity
- Uf :
-
superficial fluid velocity
- Umf :
-
superficial fluid velocity at minimum fluidization
- up :
-
downward particle velocity
- x:
-
coordinate along bed distance from distributor
- α:
-
thermal diffusivity
- α′,β′,γ′:
-
dimensionless variables, (1+ψ)e−ψ and (-hpat/ρpCppɛf)
- ψ:
-
dimensionless variable, hpy a(x/uf)/ρfCpfɛf
- ϕ:
-
dimensionless variable, hpa(t-x/uf)/ρpCpp(1-ɛf)
- ξ:
-
dimensionless variable, ψ · ϕ
- η:
-
dimensionless variable, (-hpat)/ρpCpp(1+hpaL/ρfCPpUf)
- ζ:
-
ratio of the volume of wake dragged upward behind a rising bubble to the volume of a bubble
- δ:
-
volume fraction of bed consisting of bubbles
- ɛf :
-
average voidage of the overall bed
- ɛmf :
-
voidage at minimum fluidization
- ɛfx :
-
voidage at a distance x in bed
- ɛfa,ɛfb :
-
local voidage in A zone and B zone, respectively
- λ:
-
thermal conductivity
- ν:
-
kinematic viscosity
- ρ :
-
density
- f, p:
-
refer to fluid and particle, respectively
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Seki, N., Fukusako, S. & Torikoshi, K. Characteristics of heat transfer between particles and fluid in aggregative fluidized bed. Wärme- und Stoffübertragung 14, 173–182 (1980). https://doi.org/10.1007/BF01637699
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DOI: https://doi.org/10.1007/BF01637699