Heat transfer and temperature fluctuation of lithium flowing under transverse magnetic field

For providing background information on the liquid metal cooling of fusion reactors, the MHD effects on heat transfer of flowing lithium was experimentally studied with an emphasis on temperature fluctuations. The test section was constituted of a 15.8 mm I.D., 1.65 mm thick, 316-SS tubing and a 7.6 mm O.D. heater pin with nine 0.5 mm thermocouples. The experiment covered the range of B = 0 ∼ 1.0 T, U = 0.2 ∼ 4.0 m/s, T = 320 ∼ 390 deg C and q = 0 ∼ 68 W/cm2. The results are summarized as follows: (1) With increasing magnetic flux density B, Nusselt number Nu decreases to a value of flat flow velocity model: 6.38 but rises in B = 0.1 ∼ 0.4 T. (2) The RMS of temperature fluctuation has strong dependence on B and presents a peak near B = 0.25 T. (3) The singular rise of Nu is inferred to result from enhanced turbulence due to steepening of radial gradient of velocity near the wall as a result of MHD effect. (4) The transit velocity estimated from temperature cross-correlation in the parallel sector coincides with the mean velocity when B = 0 but deviates toward a lower value with applying B. (5) Local flow velocity is decelerated in the magnetically-parallel sectors and accelerated in the perpendicular. (author)