Generalized fluid equations are derived by making an assumption for
the shape of the velocity distribution function (VDF) and then taking
velocity moments of the Boltzmann equation.  How well the assumed VDF
agrees with the actual VDF determines the accuracy of the resulting
moment equations.  Based on direct solutions to the Boltzmann equation
for a fully ionized gas in the collision-dominated limit, we have
assumed a shape for the VDF that is a Maxwellian with a third-order
correction term.  The resulting isotropic fluid equations for plasmas
of arbitrary composition improve the description of collisional
processes, particularly heat conduction and thermal forces, while
retaining the relative simplicity of "conventional" fluid equations,
allowing for easy implementation in numerical models.  Expanding about
a bi-Maxwellian results in gyrotropic transport equations that provide
a good description of both collision-dominated and collisionless flow.
We present results for the solar wind, where the equations have been
implemented and solved numerically in a model extending from the
chromosphere to Earth.