Abstract
The rates of heat transfer occurring during the counter-current contacting of dispersed liquid metals and gases in towers packed with ring and spherical packings are examined. Using mercury and air as the heat exchange fluids, heat transfer studies at room temperature are described and the heat transfer mechanisms examined. Heat transfer data are also presented for the contacting of molten lead with preheated nitrogen in a pilot plant scale apparatus. Utilizing the mercury irrigated tower as a room temperature analogue of the high temperature apparatus, the mechanisms operating at high temperature (400° to 600°C) are examined. Two basic heat transfer mechanisms operate below about 400°C: the direct mechanism, which refers to convective heat transfer across the gas/liquid metal interface, and the indirect mechanism, a complex process involving conduction and convection in a sequence such as liquid metal-solid packing-gas phase. Above about 400°C, another mechanism, radiation heat transfer between the liquid metal and its environment, is thought to become significant, but experimental errors masked its detection in the present study.
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Abbreviations
- a :
-
heat transfer area per unit bed volume, ft2/ft3
- a i :
-
liquid-gas interfacial area per unit bed volume, ft2/ft3
- a p :
-
surface area of dry packing per unit bed volume, ft2/ft3
- c :
-
specific heat at constant pressure, Btu/lb. °F
- C, Ć :
-
constant in empirical equation
- D P :
-
characteristic length of packing particle, ft (for Raschig rings and spheres,D P= average measured diameter)
- D ab :
-
binary diffusivity for system A-B, ft2/hr
- G :
-
gas mass velocity or superficial velocity, lb./hr ft2
- H E :
-
effective holdup ratio, ft3 liquid/ft3 of bed
- H g :
-
height of gas film transfer unit, mass transfer, ft
- (H t direct :
-
height of transfer unit, direct heat transfer, ft
- (H t overall :
-
height of transfer unit, overall heat transfer, ft
- h g :
-
gas film heat transfer coefficient at gas/liquid interface, Btu/hr ft2 °F
- h s :
-
gas film heat transfer coefficient at gas/solid interface, Btu/hr ft2 °F
- h r :
-
heat transfer coefficient for radiation, Btu/hr ft2 °F
- k s, kg :
-
thermal conductivity of packing, gas, Btu/hr ft °F
- L :
-
volumetric liquid rate, ft3/hr ft2
- n, m :
-
constants in empirical equation
- N t :
-
number of transfer units
- q :
-
rate of heat flow per unit cross-sectional area of bed, Btu/hr ft2
- Q :
-
rate of heat flow, Btu/hr ft3
- Q dir :
-
rate of heat transferred by the direct heat transfer mechanism between gas phase and liquid metal, Btu/hr ft3
- Qindir:
-
rate of heat transferred by the indirect heat transfer mechanism by conduction and convection, Btu/hr ft3 Qrad rate of heat transferred by radiation, Btu/hr ft3
- Qtot:
-
total rate of heat transfer, Btu/hr ft3
- t g1 :
-
gas temperature, inlet stream
- t g2 :
-
gas temperature, outlet stream
- t l1 :
-
liquid temperature, outlet stream
- t l2 :
-
liquid temperature, inlet stream
- T, t :
-
temperature, °F, °C, or °R
- T m :
-
average temperature of liquid metal in bed,°F
- ΔTlm :
-
logarithmic mean temperature, difference, °F
- (ΔT) gp :
-
mean temperature difference between gas phase and packing, °F
- (ΔT)r :
-
mean driving force for radiation, °F
- U :
-
mean overall heat transfer coefficient, Btu/hr ft2 °F
- V g :
-
true gas velocity based on irrigated porosity, ft/sec
- Z :
-
packed height, ft
- Pr:
-
Prandtl number =c ν/k
- Re:
-
Reynolds number =D pVg p/μ
- Sc:
-
Schmidt number =μ/pD ab
- α :
-
constant in empirical equation
- ε:
-
emissivity
- μ:
-
viscosity, lb./hr ft
- p :
-
density, lb./ft3 Subscripts
- g :
-
gas phase
- I :
-
liquid phase
- r :
-
radiation
- s, p :
-
solid
- x :
-
refers to axial distance, length
- 1:
-
position 1
- 2:
-
position 2
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Formerly Graduate Student, School of Metallurgy, University of New South Wales, Kensington, Australia.
Formerly Associate Professor, School of Metallurgy, University of New South Wales
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Mackey, P.J., Warner, N.A. Heat transfer between dispersed liquid metals and gases in packed beds. Metall Trans 3, 1807–1816 (1972). https://doi.org/10.1007/BF02642564
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DOI: https://doi.org/10.1007/BF02642564