Velocity distributions for a hard-disk fluid in a small circular cavity: effect of the conservation of the total angular momentum

The one-particle distribution for the modulus of the velocity of a hard-disk fluid inside a small circular cavity is studied. Due to the geometry of the cavity, the total angular momentum L is conserved if the (elastic) particle–wall collisions are specular, leading to a new, special microcanonical ensemble. The study of the finite-size effects due to the conservation of L is performed by means of molecular dynamics simulations. The one-particle distributions for the radial and the tangential components of the velocity are also analyzed.