ON THE NEED OF WRITING CORRECT BOUNDARY CONDITIONS IN GRANULAR GASES IN MICRO-GRAVITY

摘要

This paper describes recent results on the dynamics and the statistical mechanics of an ensemble of real particles that dissipates due to collision, i.e. ball-wall collision and ball-ball collisions, studied in microgravity. Special care is taken to study the limits of little interaction between the balls because of their small density number (Knudsen regime) and the limit of strong interaction when the mean free path between 2 ball-ball collision is less than the cell size. It turns out that the physics of these dissipative systems is non extensive and generates heterogeneities. In a first part we describe recent experimental results obtained in micro-gravity environment; the question of transporting and managing grains is asked, taking as an example the effect known as Maxwell's demon. Comparison with different limiting eases will be achieved, i.e. with dissipative billiard model and with the statistical mechanics of gas or of liquid. Then the problem of writing correct boundary conditions, which describes the energy source, will be addressed and it will be shown that these conditions are in some cases rather different from what is it assumed in the literature (this will be developed in the talk).