Summary
The bath temperature and the stability of the protective layer of frozen cryolite (side ledge) at the lining in aluminum cells is influenced by the magnitude of the heat transfer coefficient between bath and side ledge (hb). A low-temperature model cell with gas-induced flow was used to study the influence on hb by gas flow rate (GF), anode immersion depth (AI), and anode/side-ledge distance (ALD). The results were fitted to the relationship hb ∝ (GF·AI/ALD)0.42. A method of calculating hb when the gas-induced flow is superimposed on a horizontal flow is suggested. The model gives reasonable values of the heat transfer coefficients in industrial cells, i.e., hb= 250–600 W/m2/°K.
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Abbreviations
- AI:
-
Anode immersion depth (m)
- ALD:
-
Anode-side ledge distance (m)
- Cp :
-
Heat capacity (J/m3/°K)
- d:
-
Distance between thermocouples (m)
- g:
-
Acceleration due to gravity (9.81 m/s)
- GF:
-
Gas flow rate per unit length of anode periphery (m2/s)
- hb :
-
Heat transfer coefficient bath/side ledge (W/m2/°K)
- kb :
-
Thermal conductivity, liquid (W/m/°K)
- kd :
-
Thermal conductivity, solid biphenyl (W/m/°K)
- L:
-
Characteristic length (m)
- Lo :
-
Length of bath/side ledge interface in vertical direction (m)
- qb :
-
Heat flow from bath to side ledge (W/m2)
- qf :
-
Heat flow through frozen diphenyl layer (W/m2)
- tb :
-
Bath temperature (°C)
- t1 :
-
Liquidus temperature (°C)
- v:
-
Bath flow rate (m/s)
- Vh :
-
Horizontal component of v (m/s)
- vv :
-
Vertical component of v (m/s)
- S:
-
Coefficient of thermal volume expansion (°K−1)
- v:
-
Kinematic viscosity (m2/s)
- o:
-
Density (kg/m3)
- σ/o:
-
Kinematic surface tension (m3/s)
- Gr:
-
Grashof number g·β (tb−t1) L3/v 2
- Nu:
-
Nusselt number hb·L/kb
- Pr:
-
Prandtl number v·Cp/kb
- Re:
-
Reynolds number v·L/v
References
J. Thonstad and S. Rolseth, “Equilibrium between Bath and Side Ledge in Aluminum Cells. Basic Principles,” in Light Metals 1983, edited by E. M. Adkins, The Metallurgical Society of AIME, Warrendale, Pennsylvania, 1982, p. 415.
R. B. Bird, W. E. Stewart, and E. N. Lightfoot, Transport Phenomena, John Wiley & Sons Inc., New York, 1960, p. 333.
E. Dernedde and E. L. Cambridge, “Gas Induced Circulation in an Aluminum Reduction Cell,” Light Metals, 1975, The Metallurgical Society of AIME, New York, 1975. p. 111.
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Editor’s Note: This article appears in Light Metals 1983, edited by E.M. Adkins, The Metallurgical Society of AIME. Copyright 1982.
Mr. Solheim received his degree in metallurgical engineering from the Engineering College in Trondheim in 1977. Since graduation he has been engaged in laboratory research in the field of aluminum electrolysis, particularly the use of physical models.
Dr. Thonstad graduated from NTH with a degree in metallurgical engineering and he later received his dr.ing. and dr. techn. degrees at the same institution. He has specialized in fused salt electrolysis. Prior to his present position he was a research fellow with the Foundation for Scientific and Industrial research at NTH and conducted research at laboratories abroad. He is a member of The Metallurgical Society of AIME.
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Solheim, A., Thonstad, J. Model Experiments of Heat Transfer Coefficients Between Bath and Side Ledge in Aluminum Cells. JOM 36, 51–55 (1984). https://doi.org/10.1007/BF03338408
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DOI: https://doi.org/10.1007/BF03338408