  We do a generic study of the behavior of a hard disk system under the action
of a thermal gradient in presence of an uniform gravity field. We observe the
conduction-convection transition and measure the main system observables and
fields as the thermal current, global pressure, velocity field, temperature
field,... We can highlight two of the main results of this overall work: (1)
for large enough thermal gradients and a given gravity, we show that the
hydrodynamic fields (density, temperature and velocity) have a natural scaling
form with the gradient. And (2) we show that local equilibrium holds if the
mechanical pressure and the thermodynamic one are not equal, that is, the
Stoke's assumption does not hold in this case. Moreover we observe that the
best fit to the data is obtained when the bulk viscosity depends on the
mechanical pressure.
