HEAT TRANSFER ENHANCEMENT IN LIQUID METALS BY STATIC AND ROTATING MAGNETIC FIELDS

Application of a static magnetic field can significantly increase the Nusselt number of liquid metal (LM) forced flows. This heat transfer enhancement is attributed to the establishment, by the magnetic field, of a strongly anisotropic turbulent flow. The creation and maintenance of the enhanced anisotropic turbulence requires injection of turbulent energy (having vorticity components in the field direction). Enhancement of heat transfer in an unmoving fluid can be achieved by applying a rotating magnetic field, as will be demonstrated in the example of high heat flux removal from the LM targets for production of radioisotopes for medical applications. This problem is one of the major obstacles in the development of such targets for the Soreq Applied Research Accelerator Facility in the Soreq Nuclear Research Center. A typical target contains liquid metal exposed to high heat fluxes from the high kinetic energy of the beam of accelerated protons. Insufficient heat dispersion results in high temperature gradients on the irradeated surface which may cause severe damage to the target. The radio-isotope production targets are designed for high specific activity of a small amount of the produced material, which does not make it possible to use an external circulation system for LM mixing inside the target. A two-part solution was suggested to enhance the heat removal from the target and to decrease the temperature gradients: (1) forced convection of liquid metal by rotating magnetic field, and (2) cooling the container's body by an array of impinging water jets. Significant reduction of the peak temperature and temperature gradients within the LM was achieved.