Department of Physics and Astronomy, University of Pennsylvania, 3231 Walnut Street, Philadelphia, Pennsylvania 19104-6396, USA.
Nat Commun. 2017 Jun 1;8:15551. doi: 10.1038/ncomms15551.
Grains exiting an underwater silo exhibit an unexpected surge in discharge rate as they empty. This contrasts with the constant flow rate of dry granular hoppers and the decreasing flow rate of pure liquids. Here we find that this surge depends on hopper diameter and happens also in air. The surge can be turned off by fixing the rate of fluid flow through the granular packing. With no flow control, dye injected on top of the packing gets drawn into the grains. We conclude that the surge is caused by a self-generated pumping of fluid through the packing. The effect is modelled via a driving pressure set by the exit speed of the grains. This highlights a surprising and unrecognized role that interstitial fluid plays in setting the discharge rate, and perhaps in controlling clog formation, for granular hoppers whether in air or under water.
谷物从水下筒仓中排出时，其排出速度会突然增加，这与干颗粒料斗的恒定流速和纯液体的流速降低形成鲜明对比。在这里，我们发现这种激增取决于料斗的直径，并且在空气中也会发生。通过固定通过颗粒填充的流体流量，可以关闭激增。如果没有流量控制，注入包装顶部的染料会被吸入谷物中。我们得出的结论是，激增是由通过包装自产生的泵送流体引起的。通过由谷物出口速度设定的驱动压力来对该效果进行建模。这突出表明，在设置排放速率方面，间隙流体起着令人惊讶且尚未被认识到的作用，也许在控制颗粒料斗（无论是在空气中还是在水下）中的堵塞形成方面也起着作用。
