Jamming and Flow in 2D Hoppers

We consider jamming that occurs for the flow of dry granular materials from a hopper as the outlet size, D, is reduced relative to the particle size, d. We propose and test a model based on the simple idea that the probability of jamming on a short time, dt, is a constant, τ. This leads to the prediction that the probability of surviving until time t without jamming is an exponentially decaying function, Ps(t) = exp(−t/τ). The important physical question is what determines τ? Experiments to date have confirmed the exponential character of the survival probability. Work in progress characterizes τ(D, d), fluctuations and their possible relation to the jamming process.