The mix manifold is supplied with expelled air from the front cargo bay by the recirculation fan to reduce the pack load. How can the stale air be used again???
The air is drawn through a
high efficiency particulate air (HEPA) filter to remove very small particles at the bacteria and microorganism level. The filter is located in the distribution bay (just aft of the fwd cargo bay) upstream from the Recirculation fan and main distribution manifold and downstream from the collector shroud.
The Recirc fan creates a low pressure zone in the collector shroud in the ceiling of the forward cargo compartment which draws air from the air grilles in the pax, flight (and cargo) compartments. The air returns to the collector through the space between the sidewalls and the floor boards - cargo ceiling. The air from equipment cooling returns under the fwd cargo floor (only in flight) and helps heat the compartment.
Hope this helps......My first post here.
Scott