Experimental Determination of Convective Heat Transfer Coefficients during Molten Aluminum Purification Using Open Cell Alumina (AL2O3) Ceramics
Heat transfer during molten metal purification in open cell ceramic foams is characterized by extreme temperature gradients and transients. It starts with outflow of high temperature gases driven by the molten metal front, which is followed by the molten metal passing through the open cell ceramic structure. Finally, the temperatures of ceramic filters level out at the molten metal temperature. The purpose of this study is to experimentally determine average convective heat transfer coefficients (h) during forced convection of molten aluminium through pure alumina foams. Open cell ceramics are embedded in a sand mould for conducting the experiments. Molten aluminium is forced to pass through a series of foam modules, one atop the other with
each of them being equipped with thermocouples at inlet and . The flow velocity is determined indirectly by measuring the temperature response time of each thermocouple, and it is varied between 0.06 m sand 0.09 m/s. The alumina foams tested in this study exhibit 10 and 30 pores per inch (PPI). A comparative study of different types of thermocouples applied in different combinations is done. A one dimensional thermodynamic model assuming adiabatic wall conditions has been applied. The experimental data are presented in diagrams using fluid phase average Nusselt number, Nu, pore size Reynolds numbers, Re(por) and dimensionless fluid temperatures ?(f) measured at different positions within the foam stack.