1 Ceramic Foam Results Discussion
1.1 Priming and wetting
ceramic foam is normally operated in a ” filter Bowland is primed using a gravity head of liquid metal with a recommended pre-heating procedure. In other words, the gravity head forces the metal into and through the ceramic foam, displacing much of the entrapped air. The poor wetting characteristics of alumina aluminum “, and the need to remove the trapped air can lead to difficulties at the start of the filtration process ( particularly with high pore density filters )The typical heights of industrial priming heads are, for different grades of commercial filters, plotted in Fig . 2 . As can be seen from the figure, the presence of an electromagnetic field secures a significant reduction in the required metal head during priming.
In Fig 3 ( a ) and ( b ) metallographic pictures of the50 80PPIi ceramic foam after a gravity priming experiment with a 100 mm metal head above the filter element is presented. As can be seen from the figures the experiments failed and the molten metal solidified over the filter elements with a nearly complete lack of penetration of metal into the filters. This was, however, expected based on the industrial priming data presented in Fig . 2.
When applying a magnetic field of-0 16 T, the filters studied were nearly perfectly primed and wetted using the same 100 mm of a metal head, see Fig 3 ( c )and ( d ) representing the results obtained for 3 10 minutes of treatment time. The SEM micrographs obtained show a greatly improved wetting, as well as successful removal of gas with an increased electromagnetic stirring time. The electromagneticriming phenomena are now the subject of a patent application filed by the present authors %
2. Particle redistribution
gravity filtration it is common to observe a dense filter cake above the ceramic foam, as well as bridging and clogging in the upper part of the filter. Profound changes in the distribution of particles, both inside and below the filter media have, however. been observed in the present work due to the influence of the electromagnetic field, see Fig 4. As can be seen from the figure, when using electromagnetic forces the highest particle density obtained was observed in Area2. In addition, the backflow of the melt caused by the curl in the Lorentz forces has resulted in Area 3 also having a higher concentration of particles. Area 4 however, was nearly particle-free that cleanetal re-enters the filter from below.
The present study has proven that by applying an electromagnetic field a substantial improvement of the wetting between alumina and liquid aluminum in 30,50 and 80-PPI ceramic foam can be obtained with a significant reduction of the required metal head. Nearly perfect priming of high pore density filters was demonstrated. A redistribution of particles inside was also observed. Based on this it is clear that the electromagnetically induced bulk flow secures that the filter media do not clog and changes the filtration mode from cake filtration to deep bed and in-bed-ake-filtration for the high pore density filters.
The authors wish to express their gratitude to Egil Torsetnes ( NTNU, Trondheim, Norway ) for their help in designing and constructing the experimental apparatus. My deepest gratitude is also due to Kurt Sandaunet ( SINTEF, Trondheim, Norway ) for the use of the SINTEF laboratory and his contribution to the execution of the experiments. Also, a special Liss Pedersen ( Alcoa, Lista, Norway ) for the filter materials and Kexu Zhang ( M . Student at NTNU, Trondheim, Norway ) for providing Ceramic Foam Results Discussion permeability data.