Impact of rotating magnetic field on liquid metal flow through cylindrical channel to increase heat exchange

A mechanism for enhancing the cooling of a liquid metal flowing through a cylindrical channel is discovered. The mechanism is based on intensifying heat exchange with a surrounding medium, the temperature of which is significantly lower than the temperature of the liquid metal at the channel inlet. Action of the mechanism leads to a greater decrease in the metal temperature at the channel outlet than without its action. The intensification is performed by generating swirl flow in a region of the channel localized along its axis. The swirl is generated by an electromagnetic force created by the completely contactless action of a rotating magnetic field on the channel with the liquid metal. The features of this magnetohydrodynamic process and heat transfer are studied using mathematical modeling and experiment. The processes in two versions of channels with a through flow of liquid metal are considered. In the first variant, the channel is a cylindrical pipe of fixed diameter. In the second variant, the diameter of the cylindrical channel varied, since conical expansion and contraction were located at the inlet and outlet. For the second variant of the channel both numerical and experimental studies were performed on a gallium eutectic. In the experiment, flow characteristics were measured using an ultrasonic Doppler velocimeter probes, and temperature data was obtained by a set of thermocouples. The experimental results were used for validation the mathematical model and to qualitative confirm the heat transfer enhancement effect. For both channel variants, the dependencies of the cooling effect on the electromagnetic force are obtained. The mechanism we discovered is based on the generation of a powerful azimuthal flow, which creates a secondary poloidal vortices. The vortices intensify radial heat transfer from the hot axial region. Effective cooling is achieved by the movement of hot liquid metal predominantly near the channel wall, rather than near the axis. It is shown that flow swirl can increase heat transfer efficiency by 20 percent. In this case, the energy of the poloidal component of the flow increases by more than 2 times.