# Gas flow through porous/non-porous gas membranes

Hey,

I am new to Palabos and I am having difficulty with converting physical units into LB units. I have read the tutorial listed on the website but i am still confused in regards to converting the units. To my understanding it is better to working backwards from LB units to physical units. I can get LB units into dimensionless form but i can’t seem to convert dimensionless units to physical units.

Besides this i am not sure what Re i should be using for gas flow through my porous membrane. I read in few places that Re should be << 1 for porous media but when i put anything <<1 into the code my simulation stops working. so i am not sure what i am doing wrong.

My physical system is as follows:

length = 2cm //length of the membrane holder
width = 4cm //width of the membrane holder
flow rate = 100 cc/min //rate at which CO2 flows through the system
membrane thickness = 20E-6 m //sites in the center of membrane holder
kinematic viscosity of CO2 (@ 20c) = .091E-6 m2/s = .0546 cm2/min

my physical system looks something like this:
| : : |
| : : |
inlet >>> | : : |>>>outlet
| : : |
| : : |
membrane

My LB parameters are as following:
Umax = 1E-2
Re = 10
N = 100
Lx = 3
Ly = 1

I am looking at the CO2 permeability of through the membrane. If anyone can help me out it would be great.