An Interfacial Heat Transfer Mechanism Based Integrated Model And Its Application For Thermal Field Analysis In Aluminium Reduction Cells

In industrial production of aluminum, the thermal field in the reduciton cell directly determines energy consumption of the electrolysis process. Building reliable analytic models to precisely calculate it definitely have significances both in theoretical and practical for designing low energy consumption, high current efficiency and stable cells as well as developing new process technologies.Aims to overcome limitations of status about weak theoretical basis and low calculation accuracy, models based on interfacial heat transfer mechanism have been proposed in this thesis by the support of National Natural Science Foundation of China. These models include calculating interfacial heat transfer coefficients between cell soufaces and surroundings, interfacial heat transfer coefficients among molten electrolyte, anodes and ledge, directly modeling coulped thermal-electric field and considering effects of heat during electrochemical process. The main conclusions and achievements are as follows:(1) Combined of heat transfer theory and heat dissipation characters of cell surfaces, a model of interfacial heat transfer coefficient between cell surfaces and surroundings has been built. By following this model, a GUI(Graphical User Interface) program has been developed. Results show that the main effects on the coefficient are surface temperature and flow speed of surrounding fluids, which the former heavily affects the radiative heat transfer coefficient but slightly the convective heat transfer, and the latter only influences the convective heat transfer coefficient that the overall coefficient increases with the increase of surface temperature and flow speed of fluids. The larger capacity of cells is, the smaller the convective heat transfer coefficient. (2) Based on CFD(Computational Fluid Dynamics) theory and the wall function method, a model for calculating the interfacial heat transfer coefficient among molten electrolyte, anodes and ledge has been constructed. The numerical computation in CFX is realized. Analysis of the driving force and coefficient distribution shows that anode bubbles are the dominant force that drives heat transfer from electrolyte to anodes and to ledge. However, the electromagnetic force can-not be neglected. Thus, the two kinds of forces are takn into the account together of the calculation. On the surfaces of ledge, the coefficient distribution is determined essentially by electrolyte flow. There is a small coefficient in the bottom of the anodes due to the block of bubble layer. With slotted anodes, the coefficient increases with the decrease of gas volume beneath the anodes, but decreases at ledge surfaces as the electrolyte flow is weaken.(3) Based on the analysis of energy income and expense, and the thermal-electric balance principle, an integrated model directly coulped the thermal-electric field for aluminum redcution cells was been set up. Effect of heat during electrochemical process and interfacial heat transfer coefficient are considered into this model. Finally, by using the integrated model, the thermal-electric field of a500kA aluminum reduction cell is calculated in ANSYS and its use is analyzed.