Countercurrent flow in systems of parallel narrow rectangular channels

The countercurrent flow performance of a system of parallel narrow rectangular channels is examined experimentally and theoretically. The experimental test section is a full scale model of a High Flux Isotope Reactor (HFIR) fuel element assembly which consists of two concentric annuli filled with aluminum plates of 1.27mm thickness separated by 1.27mm flow channels. The plates are curved as they go radially outward to accomplish a constant flow channel width and constant metal to coolant ratio. The width of the flow channels in the outer annulus when straightened is 75mm and the width of the channels in the inner annulus is 84mm. The length of all channels is 0.61m. A review of countercurrent flow data developed from experiments using single narrow channel test sections is presented and a mechanistic model for countercurrent flow in narrow channels is developed that predicts these data reasonably well. The treatment of countercurrent flow in systems of parallel channels is presented and a technique to determine the countercurrent flow performance of a single channel in the parallel channel situation is developed. The experimental results indicate that the performance of an individual channel in the parallel channel system is consistent with data taken in experiments using a single channel, despite the significant differences in channel exit conditions.