Velocity and Heat Flow in a Composite Two Fluid System
  We describe the stress energy of a fluid with two unequal stresses and heat flow in terms of two perfect fluid components. The description is in terms of the fluid velocity overlap of the components, and makes no assumptions about the equations of state of the perfect fluids. The description is applied to the metrics of a conformally flat system and a black string. 
J. P. Krisch and E. N. Glass
gr-qc