Flow uniformity in rock beds

Abstract Although theories on rock bed behaviour assume uniform flow across the bed, measurements on real beds show that the flow is actually non-uniform. By experiments on a full-scale rock-bed, this paper established the cause and magnitude of non-uniform flow. The cause is pressure-variations in the plenums. The magnitude, as measured by the coefficient of variation r of the velocity profile, is typically on order r = 0.2; as measured by the peak-to-peak variation in velocity, it is as high as 125 per cent. The paper also theoretically estimates the effect of non-uniform flow on the total system performance. The effect is small provided r ⩽ 0.3, but it is substantial if r ⋍ 1.0 .