non-equilibrium boundary conditions for flow in porous media

Hello everyone!!
I am a bit new to LBM and trying to simulate flow in porous media. I came across non-equilibrium distribution function boundary conditions somewhere.
but could not understand [e][/a] which refers to internal energy and [e][/a] and [e][/b] are in opposite direction…
can you please tell me what it is and how to put I into a LBM code?
thank you so much…