Is Dissipative Granular Gas in Knudsen Regime Excited by Vibration Biphasic ?

TL;DR

This paper compares a recent vibrated granular gas model with micro-gravity experiments, confirming impact distributions but revealing a second nearly stationary phase, and discusses the piston role as impact generator versus thermostat.

Contribution

It demonstrates the model's agreement with impact distributions in micro-gravity and introduces the concept of a second phase of nearly at-rest balls affecting impact counts.

Findings

Impact distribution follows an exponential law both experimentally and theoretically.

Discrepancy in impact counts suggests existence of a nearly stationary second phase.

Model predicts different behaviors in 1g and micro-gravity conditions.

Abstract

Compatibility between a recent model (Poudres & Grains 15, 1-17, (2005)) of vibrated granular dissipative gas and recent experimental results in micro-gravity is investigated. It is found a good agreement for the distribution of impacts, which is found to vary exponentially as P(mv) = exp-(v/vo), both experimentally and theoretically; hence it confirms the distribution f(v) of speeds varying as (1/v) exp(-v/vo). However, some discrepancy is found for the variation of the total number of impacts with the number of balls contained in the cell. This is attributed to the existence of a second phase of balls "nearly at rest". Compatibility between results from granular gas experiments in micro-gravity and experiments on Maxwell's demon in 1-g is also discussed. The main idea, which allows understanding these results is to consider the piston as playing the role of an impact generator or of a "velostat" instead of a thermostat. It is shown also that the model predicts completely different behaviours in 1g and in 0g. Pacs # : 05.45.-a, 45.50.-j, 45.70.-n, 81.70.Bt, 81.70.Ha, 83.10.Pp