Air Mix manifold 737ng

[godu]

Can some one solve this tech:

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?????

[spannersatKL]

The mix manifold is located behind the fwd cargo bay not 'in' the bay....so no air from the bay is used. In fact the cargo bay is effectively sealed from the cabin in flight. The air in the bay where the mix manifold is located is part of the under floor area. Air enters the pax cabin at the top of the cabin, circulates inside the cabin and exits at foot level in the side walls, to the underfloor area. It can then flow towards the outflow valve and over board and some can flow towards the recirculation system and the mix manifold where it is recirculated.

[Denti]

Interesting, the system description for us drivers reads:

The recirculation fan system reduces the air conditioning system pack load and the engine bleed air demand. Air from the passenger cabin and electrical equipment bay is drawn to the forward cargo bay where it is filtered and recirculated to the mix manifold. The fan is driven by an AC motor. The fan operates with the recirc fan switch in AUTO except with both packs on and one or both in HIGH.

That seems to indicate that the forward cargo hold is heated and ventilated by the used air from the electrical equipment compartment and used cabin air.

[STBYRUD]

I was reading that just yesterday, but that must be bad wording - after all its a fire class C compartment. I suppose the equipment cooling air is first drawn around the forward cargo compartment, mixed with the cabin air in some kind of plenum chamber for recirculation (and ends up in the mix manifold) or is channeled to the outflow valve directly.

[AviationGlossary]

737NG Air Circulation

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