Measurements of turbulent flow in axially finned rod bundles

The hydraulic characteristics in subchannels of axially finned rod bundles installed in the Korea Multipurpose Research Reactor (KMRR) were measured using one-component laser-Doppler velocimetry (LDV). Pressure drops for each component, time mean axial velocity, and axial turbulent intensity were measured. Then the friction factors in rod bundles were estimated from the measured pressure drops. The turbulent crossflow mixing rate between neighboring subchannels was evaluated from the measured data. The results show that (1) the friction factors for axially finned rod bundles are less than those given by Moody's correlation for smooth tubes, and (2) as the flow develops, the turbulent crossflow mixing rate between neighboring subchannels decreases and, in the developed region, the values level out.