Trapped field potential of commercial Y-Ba-Cu-O bulk superconductors designed for applications

Bulk high-temperature superconductors (HTSs) that act as a trap field magnet establish a novel type of magnetic field source, which is significantly different from that of a permanent magnet or solenoid; therefore, they can be potentially used in magnetic-force-based applications. However, the primary issues related to the commercial use of the bulk HTS technology are established on the enhancement of trapped magnetic fields, as well as their reliability and reproducibility at temperatures achievable with off-the-shelf cryocoolers. This study presents experimental investigations on the strong trapped magnetic fields observed in commercial Y-Ba-Cu-O bulk HTSs produced as a double-sample stack, a cylindrical bulk, and a ring-shaped bulk. Consequently, a reliable and reproducible magnetic field of 9.5 T at 50 K was trapped in commercial Y-Ba-Cu-O assembled as a double-sample stack. In this case, shrink-fit encapsulation with either aluminum or stainless steel tube ensured equally effective reinforcement. Higher magnetization, although accompanied with partial flux jumps, yielded a trapped field of 16.85 T at 30 K, which is comparable to the reported record trapped fields. Finally, a maximum trapped field of 9.78 T - the strongest trapped field reported to date - was attained in the 6 mm hollow space of the ring-shaped bulk HTS

Electromagnetic stirring of glass melts using Lorentz forces - Experimental results

The question as to whether it is possible to stir glass melts using electromagnetic (Lorentz) forces has been controversially discussed in the past. Α series of accurate experiments is reported in which the buoyancy driven motion of a directly electrically heated glass melt in a cylindrical crucible has been modified by applying an external alternating magnetic field. Using temperature measurements directly in the melt it is demonstrated for the first time that the Lorentz force created in the melt leads to a homogenization of the temperature and density distributions because of an enhancement of the flow. Moreover, evidence is provided for an improvement of the glass homogeneity. The feasibility analysis provides rational possibilities for the application of magnetic fields for electromagnetic flow control in glassmaking processes

Modelling of EM glass convection

Purpose – To develop the mathematical model, which allows predicting the temperature and flow distribution of an opaque glass melt with the temperature-dependent properties in case it is generated by electromagnetic and thermal convection. Analysis has been done for geometry of the model crucible with the immersed rod electrodes. Numerical analysis is used as a tool for finding out the parameters of the system, which allow getting desiderated homogeneity of temperature field by EM action. Design/methodology/approach – ANSYS CFX software is implemented for coupling of EM, thermal and HD processes in the modelled system. Usability of non-inductive approximation is shown using a full harmonic analysis in ANSYS. Findings – External magnetic field can impact the temperature distribution in the whole volume of the melt significantly, it relocates the hottest zones and changes the maximal temperature in the melt. Qualitative agreement between the numerical and experimental results has been obtained. Dependence of the potential difference between the electrodes on the velocity and temperature range has been examined. Impact of different thermal boundary conditions has been analysed. Research limitations/implications – Effects analysed in the publication occur in each conducting media subjected to the impact of simultaneous electrical and magnetical field. The main limitation is non-transparency of the melt. Practical implications – The purpose is to develop a mathematical tool for parameter optimisation of real glass melting furnace. Originality/value – In the present model temperature dependent properties of the melt have been taken into account, which has been neglected in previous models

Lorentz force velocimetry using a bulk HTS magnet system: proof-of-concept

This paper presents a proof-of-concept of the idea of using bulk high-temperature superconducting (HTS) materials as quasi-permanent magnets that would form, in the future, an integral part of an advanced Lorentz force velocimetry (LFV) system. The experiments, calculations and numerical simulations are performed in accordance with the fundamental theory of LFV, whereby a moving metal rod passes through a static magnetic field, in our case generated by the bulk HTSs. The bulk HTS magnet system (MS) consists of two Y-Ba-Cu-O samples in the form of bulk cylindrical discs, which are encapsulated in an aluminium holder and wrapped with styrofoam. The aluminium holder is designed to locate the bulk HTS magnets on either side of the metal rod. After field cooling magnetisation with an applied field of 1.5 T at 77 K, the bulk HTS MS provides a quasi-permanent magnetic field over 240 s, enabling Lorentz force measurements to be carried out with a constant velocity of the metal rod. Two sets of Lorentz force measurements with copper and aluminium rods with velocities ranging from approximately 54-81 mm s-1 were performed. The obtained results, which are validated using a numerical model developed in COMSOL Multiphysics, demonstrate the linear relationship between the Lorentz force and velocity of the moving conductor. Finally, the potential of generating very high magnetic fields using bulk HTS that would enable LFV in even weakly-conducting and slow-flowing fluids, e.g., glass melts, is discussed