Net driving force refers to the driving force upstream minus driving force downstream.
As an example: in a gas membrane, the driving force is a fugacity difference across the membrane. In most applications this can be calculated as a partial pressure difference, so if there is 60 psig of a pure gas on the top, and 0 psig on the bottom, I have a 60 psi driving force. If I have 60 psig on the top, and 15 on the bottom I have a 45 psi driving force.
Not all membranes use pressure as the driving force. (from wiki) "The driving force of the material transport is given by concentration, pressure, electrical or chemical gradient across the membrane" However, I am a gas membrane guy, so I think in terms of partial pressure gradient.
Dave Hasse
Air Liquide
dave.hasse@airliquide.com
