The model proposed by Felicelli, Heinrich, and Poirier is used to simulate the solidification of a small two-dimensional domain of Pb-10 wt pct Sn alloy in the presence of electromagnetic stirring by different traveling fields, with or without gravity. Results show (a) enrichment of the bulk liquid by mush solute draining; (b) spontaneous formation of vertical channels, acting as ducts, significantly modified by the electromagnetic flow; and possibly (c) a finer periodic structure of subchannels. Only the last feature is sensitive to the mesh size and permeability value. Scaling analysis is used to balance Darcy, buoyancy, and electromagnetic phenomena. Attention is focused on the gradient zone at the solidification front. Electromagnetic forces can change the flow structure in the bulk liquid. In this way, they modify the pressure differences at the solidification front, changing the channel segregation pattern. Although they cannot eliminate the channels, they can control their positions and partly prevent the unsteadiness of buoyancy effects.
A numerical investigation of directional solidification of Al-7wt.%Si alloy stirred by a rotating magnetic field is compared with experimental results. Experimental study of such process has revealed periodical macrosegregation in axial direction of the samples in the shape of a “Christmas tree”. Similar macrosegregation pattern is obtained in simulations for the two values of magnetic field. Numerical simulations have shown also that formation of the periodical structure depends not only on the external conditions but on the permeability of the mushy zone.
Frequency conversion studies conducted upon polycrystalline ferrites and yttrium iron garnets have established that microwave mixing displays a linear dependence upon input powers. Sum and difference signal powers generated in ferrites and garnets were examined as a function of rf power and sample shape. Conversion efficiencies of −14 db for sum signal output and −36 db for difference signal output were achieved for magnesium manganese ferrite at X band.
A multiple signal con,,:ersion P!ocess has been ~bserved in ferrimagnet ic materials at microwave frequencies. The second harmOniC of the mput frequency IS generated in a magnetized ferrite and caused to mix with th. e .fundam ent~l.rrequency in the specimen generating the harmonic. A portion of the upper side band power ar~smg from ~llIxmg o~ the fundamental frequency and its second harmonic is constructively added to the third ha~momc occurring from harmonic generation. The total output power at the third harmonic is consequently mcreased.
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