Jamming or crowding is a common phenomenon in daily life. Think of people passing through a lane. The flow rate is greater if people move faster. However, if the number of the people swarming in keeps increasing, at some point the flow will freeze. In another scenario, when the rate of the flow remains unchanged, it still could be crowded if the lane suddenly become narrower. A recent study by CAS researchers has shed light on the physical properties of the phenomenon.
It is believed by physicists that the diverse phenomena of traffic flow, pedestrian flow, and floating ice are related to the nonlinear behaviors of granular materials, which can exhibit both solidlike and fluidlike behaviors. In a study of dilute-to-dense transition of granular flow of particles in a two-dimensional channel, researchers Hou Meiying and Lu Kunquan, et al from the CAS Institute of Physics found that there exists a maximum inflow rate, above which the outflow changes from dilute to dense and the outflow rate drops abruptly. In their paper published on Nov. 14 issue of Physics Review Letters
, the CAS researchers reported that the transition occurs when the area fraction of particles near the exit exceeds a critical value, which is close to 0.65.
Properties of granular flow are quite different from that of fluid motions in general terms. The discovery of this global scaling property, say the scientists, may provide ideas of better designs for the transport of granules in industrial processing, and better understanding of similar flow systems, such as that of traffic.