Heat transfer of lithium single-phase flow and helium–lithium two-phase flow in a circular channel under transverse magnetic field

Characteristics of pressure drop and heat transfer have been investigated for a lithium single-phase flow and a helium-lithium two-phase flow in a horizontal conducting circular channel in the presence of a uniform transverse magnetic field up to 1.4 T as related to the lithium cooling for magnetic-confinement fusion reactors. By the application of the magnetic field to the lithium single-phase flow, remarkable heat transfer enhancement has been observed at the top wall due to the suppression of the mixed convection occurring in the low Peclet number range, while appreciable heat transfer deterioration appeared in the high Peclet number range. It has been confirmed that the helium-lithium two-phase flow can reduce the high magneto-hydrodynamic (MHD) pressure drop in a lithium single-phase flow, and it can provide much better heat transfer performance than that in a helium single-phase flow. In the presence of the magnetic field, heat transfer coefficient drastically changed at the top wall, while heat transfer deteriorated at the left, right and bottom walls, possibly because the two-phase flow regime changed from the wavy flow to the annular flow. Based on measured wall temperature fluctuations, the heat transfer mechanisms of the lithium single-phase flow and the helium-lithium two-phase flow are discussed.