Design of Circular, Square, Single, and Multi-layer Induction Coils for Electromagnetic Priming Using Inductance Estimat
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THE most commonly applied metal filtration system uses Ceramic Foam Filters (CFFs).[1] To use CFFs for filtration, they must be filled with metal, and the air they initially contain must be removed. This process is referred to as ‘priming’. It is remarkably difficult to overcome the high surface energy of liquid metals such as aluminum and achieve an adequate degree of priming, especially without preheating of the filter. The concept of applying electro magnetic (EM) fields to more effectively achieve priming of commercial CFFs using a greatly reduced metal ‘head’ has been studied by the present authors in earlier publications,[2,3] and it is the subject of an international patent application.[4] The gradient in the induced Lorentz forces generates strong Magneto-Hydro-Dynamic (MHD) mixing, which in turn produces a velocity field (velocity ‘head’) that assists the metal in overcoming the surface tension between the metal and the filter media. As a result, the metal can penetrate the filter (the initial stages of priming). In addition, the MHD can produce a meniscus above the filter, which can add to the natural gravity head and further assist the priming of the filters. The magnetic field and induced Lorentz forces produced by this concept are presented schematically in Figure 1 using a 2D-axisymmetric COMSOL model.
ROBERT FRITZSCH, MARK W. KENNEDY and RAGNHILD E. AUNE are with the Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway. Contact e-mail: robert.fritzsch@ ntnu.no Manuscript submitted March 22 2017. Article published online November 20, 2017. 252—VOLUME 49B, FEBRUARY 2018
The demands on priming systems are substantially different from the requirements in the existing EM pumping systems used for liquid metals. Extremely powerful Lorentz forces are required, but only for short periods of time to overcome the metal surface energy and force the metal into the chilly air filled pores of the filter. The focus of the present study has been on the design methodology for the induction coil itself, and how it can be practically designed to create the flux density and high Lorentz forces required to achieve the priming. The present research approach was driven by the need to produce large flux densities on a very intermittent basis, while at the same time provide space for the required physical and thermal protection required in an industrial filter box setup. This necessitated the use of small liquid cooled hollow conductors operating at unusually high current densities > 25 A/mm2. Traditional measures of the electrical efficiency of a coil were therefore not included in the present design process. The practical design, validation, and construction of square and round single and double coils can be made by the use of the well-known equations from Wheeler,[5,6] together with the analytical mathematics described by Baker[7] and Vaughan and Williamson.[8] The analytical equation for the estimation of the time averaged Lorentz forces produced by short coil
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