knudsen in water flow in nanochannel

hi dears , i am simulatin water flow in nanochannel with lammp .
i want to get the knudsen number in my channel , kn=(lambda / h) , h is the height of the channel that i have that ,
lambda is the average distance that a molecule moves freely alonely till touch another molecule ,
but how i can get the amount of average lambda in channel ? is there a command in lammps for get the lambda?
thanks dears .

The mean free path in a liquid is on the order of the molecular size,
lambda ~ sigma. The Knudsen number is therefore always smaller than 1.
Liquid/solid slip at the nanoscale is fundamentally different from
Knudsen slip in a gas flow. There are several reviews in the
literature discussing liquid/solid slip and its molecular mechanisms.

Best,
Laurent

2013/8/6 Ilia Iliana <[email protected]...>: