Natural convection with dissipative heating

We derive a system of equations which models the motion of linear viscous fluids that undergo isochoric motions in isothermal processes but not necessarily isochoric ones in non-isothermal processes. The main point is that in contrast to the usual Oberbeck-Boussinesq approximation we do not neglect dissipative heating. We study Rayleigh-Bénard convection for our system and investigate existence, uniqueness and regularity of solutions and conditions for the stability of the motionless state.