The friction characteristics and velocity distribution of pulsatile flows in a rod bundle

The transient fluctuation of flow rate in a nuclear reactor is a common phenomenon in floating reactors and possible accident scenarios, the response for transient flow determined the damage threshold of fuel assemblies. Friction characteristics and velocity distribution of low-frequency pulsatile flows in a rod bundle have been studied. The experiments were conducted under the time-averaged Reynolds number 1000ta<10000, a comparison of pressure drop and velocity between steady flow and pulsatile flow was conducted. The results indicate that: (1) the averaged pressure drop in pulsatile flows is higher than one in the corresponding steady flows; (2) the averaged pressure drop in pulsatile flows is independent on the pulsation period. The velocity distribution of rod bundle in a whole pulsation period was obtained using PIV technique. The discrepancies of the velocity distribution between the steady flow and unsteady flow were analyzed. In pulsatile flows, during the acceleration portion of the period, the velocity in the rod bundle is improved. During the deceleration portion of the period, the lateral velocity in the rod bundle is improved. The results describe pulsatile behaviors in the rod bundle to contribute a better understanding of transient flow characteristics in fuel assemblies. (author)