Plate Theory and Extensions - The Compressibility of the Mobile Phase > Page 21
Now, the mass of mobile phase passing any point in the column must be conserved (i.e., the mass of fluid passing any point in the column per unit time is constant), consequently, the product of pressure and flow rate will be constant at all points along the length of the column. Thus, under isothermal conditions,
PiQi = PoQo
where (Qi) is the volume flow of mobile phase into the column at
and (Qo) is the flow of mobile phase from the column at (Po).
Now, at a position (x) along the column,
Qx = afux
where (af) is the cross-sectional area of the column available for
gas flow and is assumed constant for a well-packed column.