# Poiseuilles Law for simple structures.

## Hydraulic conductivity for a flow in a tube

For a tube, with smooth border, saturated with a given fluid
of viscosity , we
can compute the flux *q* of fluid generated by a difference of pressure
at the extremity of the tube using poiseuille law. For a tube of radius *r*
and length *l*, the flux is given by:

## Hydraulic conductivity for a flow between parallel plates

For a fracture, with smooth border, saturated with a given fluid
of viscosity , we
can compute the flux *q* of fluid generated by a difference of pressure
at the extremity of the fracture using poiseuille law. For a fracture of width
a, aperture l and length L, the flux is given by: