The Boeing Triple 7

Peter Duniho wrote:

The only way I can see for a jet to have "a reputation for being
very dry" is for the jet to be equipped with a DEhumidifier. Which, of
course, they aren't.

Both heating and air conditioning systems are dehumidifiers.

George Patterson
"Naked" means you ain't got no clothes on; "nekkid" means you ain't got
no clothes on - and are up to somethin'.

"George Patterson" wrote in message
news:kbmle.263$zb.134@trndny04...
Both heating and air conditioning systems are dehumidifiers.

How so?

When cooling air below ambient, an air conditioner does dehumidify. But the
net temperature change in an airliner is positive, and it's heated before
it's cooled. No loss of moisture there. Heating air does lower the
*relative* humidity, but that doesn't mean that moisture has actually been
removed (which is what dehumidifying is). No loss of moisture there either.

At what point is it that you believe moisture is actually *removed* from the
cabin air in an airliner?

Pete

"Peter Duniho" wrote

At what point is it that you believe moisture is actually *removed*
from the cabin air in an airliner?

Qouting from my B-707 and B-727 Flight Manuals:

WATER SEPARATOR
A water separator is installed in the Air Cycle Machine turbine
output duct to remove water by centrifugal action from the cold
air.
ANTI-ICING CONTROL VALVE
An anti-icing control valve is installed to automatically route
warm air from the Primary Heat Exchanger into the water separator
to prevent icing when airflow temperature drops below 40 degrees.


When the water separator valve does ice-up, it starts snowing
from the air conditioning vents in the cabin.

Bob Moore
17 years in the Boeing 707
PanAm (retired)

"Bob Moore" wrote in message
. 122...
Qouting from my B-707 and B-727 Flight Manuals: [...]

Perhaps I should clarify that my question pertains to cruise flight at
altitude, since that's the issue here. I would be surprised if the systems
you're describing are needed at FL390.

Peter Duniho wrote:

At what point is it that you believe moisture is actually *removed* from the
cabin air in an airliner?

If you're near the ground, in the A/C units. Higher up, it's removed in the
atmosphere. Cold air won't hold much moisture, and it precipitates out. The
heater doesn't add any.

George Patterson
Why do men's hearts beat faster, knees get weak, throats become dry,
and they think irrationally when a woman wears leather clothing?
Because she smells like a new truck.

"George Patterson" wrote in message
news:yV5me.13466$Ib.2690@trndny03...
If you're near the ground, in the A/C units. Higher up, it's removed in
the atmosphere.

Well, that's my point. Climb and descent aren't long enough to affect
whether one jet is "drier" than another or not. Whatever effect exists, it
would have to happen during cruise. I see no way for such an effect to
exist.

Pete

George Patterson wrote:

Peter Duniho wrote:


The only way I can see for a jet to have "a reputation for being very
dry" is for the jet to be equipped with a DEhumidifier. Which, of
course, they aren't.


Both heating and air conditioning systems are dehumidifiers.

Yes, but one affects only RH, while the other actually removes water
from the air.


Matt