Effect of Crucible Wall Roughness on the Laminar/Turbulent Flow Transition of the Ga75In25 alloy Stirred by a Rotating Magnetic Field

Abstract

This chapter highlights the effect using extremely different wall roughness values. As the experiments were performed at room temperature, the Ga75In25 alloy was used from the usually used low melting temperature metals and alloys. The critical magnetic induction (Bcr) values of a melt flow produced by a rotating magnetic field (RMF), remaining laminar or turbulent, are essential in different solidification processes. In an earlier paper [1], we showed that Bcr depends on the crucible radius (R) and frequency of the magnetic field (f). The pressure of the melt changes if the melt is rotated without a free surface, that is, in a closed tank. However, the pressure could be measured directly along the radius. Using ten different wall materials, we determined the angular frequency ( \(\omega\)) and Reynolds number (Re) as a function of the magnetic induction (B) and f using two different measuring methods (pressure compensation method, PCM; height measuring method, HMM). Many different crucible materials were used in the solidification experiments to study the effect of magnetic stirring on the solidified microstructure. The experiments were performed at room temperature; therefore, the Ga75wt%In25wt% alloy was chosen for the experiments. Based on the measured and calculated results, a simple relationship was determined between Bcr and Re*, f, R, and W.R., where the constants K₁, K₂, K₃, and K₄ depended on the physical properties of the melt and wall material: 

BCR( Re* , f , R , WR ) = \(\frac{Re^*}{R^2}\) (K₁ f^-K2  + K₃ f^-k4 WR)