Forced convection heat transfer and temperature fluctuations of lithium under transverse magnetic fields

The MHD effects on a heat transfer of liquid lithium flowing in an annular channel were studied, using a newly constructed comparatively large-scale lithium loop. The data on the heat transfer characteristics were arranged in Nu-St diagrams where St=Ha2/Re. The diagrams indicate that Nu decreases as St increases as a whole trend. However, singular peaks of Nu were observed at about St=13, corresponding to the singular increments of temperature fluctuations, whereas the peaks occurred at St=1.5 in the previous experiment with a smaller channel. In considering a predominant MHD effect due to conductive wall duct, the current load factor KP for external circuit was taken into account. And Miyazaki number Mi=KPSt, which means the effective electromagnetic interaction, was adopted in substitution for St and the heater pin diameter was taken as the characteristic length in place of the conventional hydraulic equivalent diameter. Thus, an appreciably good agreement was obtained concerning the peaks at Mi=0.13 in the previous and at Mi=0.14 in the present experiments. Generation of vortex series in the singular phenomena was suggested from both the periodicity of temperature fluctuations in their PSD analysis and the proportionality between peak frequency and mean flow velocity, resulting in a 32 mm interval length of series. (author)