Effect of Crucible Wall Roughness on the Laminar/Turbulent Flow Transition of the Ga75In25 alloy Stirred by a Rotating Magnetic Field | Chapter 2 | Effect of Microgravity and Magnetic Steering on the Melt Flow and the Microstructure of Solidified Alloys

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 ( w ) 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 ) = Re*/R2 (K1 f-K2  + K3 f-k4 WR)

Author(s) Details:

András Roósz,
HUN REN- University of Miskolc, Materials Science Research Group, Hungary and Institute of Physical Metallurgy, Metal Forming, and Nanotechnology, University of Miskolc, Hungary.

Arnold Rónaföldi,
HUN REN- University of Miskolc, Materials Science Research Group, Hungary and Institute of Physical Metallurgy, Metal Forming, and Nanotechnology, University of Miskolc, Hungary.

Mária Svéda,
HUN REN- University of Miskolc, Materials Science Research Group, Hungary.

Zsolt Veres,
HUN REN- University of Miskolc, Materials Science Research Group, Hungary and Institute of Physical Metallurgy, Metal Forming, and Nanotechnology, University of Miskolc, Hungary.

Please see the link here: https://stm.bookpi.org/EMMSMFMSA/article/view/13077

Determination of Laminar/Turbulent Flow Transition Using Pressure Compensation Method for Ga75In25 Alloy Stirred by RMF | Chapter 1 | Effect of Microgravity and Magnetic Steering on the Melt Flow and the Microstructure of Solidified Alloys

Melt flow has a very significant influence on the microstructure formed during solidification. Due to the formation of vortices, turbulent flow significantly affects the formation of macro-segregation than laminar flow, for example, in continuous steel casting, where magnetic stirring is an industrial practice. Several software programs have recently been developed to simulate solidification processes, where melt flow induced by magnetic stirring is also considered. However, in practical cases, it is almost impossible to prove by experiments what the type of melt flow was; at most, it can be deduced somewhat from the microstructure.

 

The effect of melt-flow on the microstructure has been investigated by performing several unidirectional solidification experiments where the melt has been flown in a rotating magnetic field. It is well-known that the angular frequency of the melt cylinder always differs from the angular frequency of the magnetic field. However, it proved to be very difficult to determine during the experiments. In our present study, the magnetic Taylor number and the Reynolds number were determined as a function of the radius of the melt cylinder, the magnetic induction, and the angular frequency of the magnetic field using the real angular frequency defined by the so-called pressure -compensation method developed earlier in the case of Ga75In25 alloy. The simulations developed for performing similar experiments can be checked, and the different experiments can be compared correctly using the obtained measurement results. By knowing the critical Reynolds number belonging to the laminar/turbulent flow transition, the value of critical magnetic induction belonging to the transition has been determined as a function of the radius of the melt cylinder. With the described experimental method, it has been possible to determine at what magnetic induction the flow would be turbulent. The results can be used to validate the software, and then validated software has a good chance of characterizing the flow of practical technologies.

Author(s) Details:

Arnold Rónaföldi,
HUN REN- University of Miskolc, Materials Science Research Group, Hungary and Institute of Physical Metallurgy, Metal Forming, and Nanotechnology, University of Miskolc, Hungary.

Zsolt Veres,
HUN REN- University of Miskolc, Materials Science Research Group, Hungary and Institute of Physical Metallurgy, Metal Forming, and Nanotechnology, University of Miskolc, Hungary.

András Roósz,
HUN REN- University of Miskolc, Materials Science Research Group, Hungary and Institute of Physical Metallurgy, Metal Forming, and Nanotechnology, University of Miskolc, Hungary.

Please see the link here: https://stm.bookpi.org/EMMSMFMSA/article/view/13076