Density of air for calculating the mass flow rate from Darcy's law
 

Hi,

I use Darcy's law to calculate first the volumetric flow rate of air through a porous material. From this I want to calculate the mass flow rate namely the product of the volumetric flow rate and the density. However the density is function of the pressure. Is it right the use the mean pressure of the input and output pressure in order to calculate the density of air?