Research Of Liquid Metal Flow Driven By Permanent Magnetic Field

Magnetic fields and electromagnetic forces have long been used to control the flow, heat and mass transfer of liquid metal since the characteristics of non-contact and cleanness. Nowadays, the current-carrying coils magnetic fields were widely applied to the industry, especially metallurgical industry, but they also had the defects of heaviness and huge power consumption. Although the application of the permanent magnetic fields may restricted by the Curie temperature of the permanent magnets, they also had the features of large magnetic flux density, flexible design, simple structure and energy saving. Thus, they can be apply to some special occasions such as complex working conditions, narrow working spaces, lower working temperature, etc. Therefore, in this dissertation, we exploited various permanent magnetic fields to agitate the GalnSn alloy, and the resulting flows were also investigated deeply.The numerical simulations and experimental measurements were performed to study the distribution of magnetic flux density in helical permanent magnetic field (HPMF) and Halbach helical magnetic field (HHMF). The comparison results showed that the distribution of magnetic flux density of HPMF via accumulating a series of permanent magnets is close to the ideal HPMF. The distribution of magnetic flux density on each helical curve of HHMF concentrated in two localizing regions and its decay is faster than HPMF.The velocity distributions of liquid GaInSn enclosed in HPMF and HHMF were measured quantitatively using ultrasonic Doppler velocimetry (UDV). The meridian secondary and global axial flows were observed in two types of helical magnetic fields. The dimension ratio of DIH and the stagger angle of the neighbor unit-structures play an important role in the transitions between these two flow patterns. For HPMF and HHMF, the transition zone was 1.25<D/H< 1.375 and 1.375<D/H<1.5, respectively.The secondary and global axial flow patterns both reveal the transient process, whose direction of liquid metal flow was distinctly opposite to steady phase, when the HPMF moved from rest, and the transient time was less than 1 s. When the HPMF was modulated, the flow direction of global axial flow could periodically inverse with the stirrer while the secondary flow could not. The modulation frequency fm played an important role. A well optimal modulation frequency, under which the averaged axial velocity reached maximum and the magnetic field can stir the liquid metal efficiently, existed both in the flow patterns of secondary and global axial flow (fm=0.1 Hz and 0.625 Hz, respectively).In this dissertation, we also proposed an innovative fluid-driven electromagnetic stirring technique which can be used anywhere in interior of the liquid metal and the prototypical experiment was performed. The flow rate of the driving fluid can be significantly varied, enabling the control of the electromagnetic force and resulting velocity field. The velocity field of the GaInSn alloy measured by UDV indicates that the fluid-driven electromagnetic stirring method can generate a velocity on the order of cm/s across the entire vessel. Thus, this technique is an effective method for stirring liquid metal.