  It is well known that collisionless systems are dissipation free from the
perspective of particle collision and thus conserve entropy. On the other hand,
processes such as magnetic reconnection and turbulence appear to convert
large-scale magnetic energy into heat. In this paper, we investigate the
energization and heating of collisionless plasma. The dissipation process is
discussed in terms of fluid entropy in both isotropic and gyrotropic forms.
Evolution equations for the entropy are derived and they reveal mechanisms that
lead to changes in fluid entropy. These equations are verified by a
collisionless particle-in-cell simulation of multiple reconnecting current
sheets. In addition to previous findings regarding the pressure tensor, we
emphasize the role of heat flux in the dissipation process.
