Temperature Fluctuation of Sodium in Annular Flow Channel Heated by Single-Pin with Blockage

Abstract

Root mean square (RMS) value and power spectral density (PSD) of temperature fluctuation were measured with use of forced-circulating sodium in an annular channel (6.5 mm I.D., 20 mm O.D.) with a concentric disk to simulate blockage (about 80%) of sodium flow. The experimental range of the heat flux was 40–150 W/cm² and the bulk flow velocity 0.14–0.41 m/sec (Re = 7.7 × 10³-2.3 × 10⁴) under a temperature of 500–800°C. The RMS value measured at the exit of heating section (150 mm downstream from the blockage) is larger by a factor of 2~3 than that in the wake (10~20 mm downstream from the blockage), marking a few deg. C for a heat flux of 105 W/cm² and a flow velocity of 0.27 m/sec. The RMS value is proportional to the wall-to-bulk-fluid temperature difference in heat transfer, presenting the similar dependence on the heat flux and flow velocity. The fluctuations of temperature are greately attenuated in the upper unheated section where the radial temperature gradient is absent, and consequently it is suggested that the fluctuations of temperature should be caused by the local turbulence of flow, such as a vortex street due to blockage in the present experiment, under the presence of large gradient of temperature near the heating surface.