What is this white smoke inside the cabin?

22 December 2020, 13:04

When an aircraft starts its operation, things like white vapor appear in the air conditioning vent points. This event has always been a source of curiosity for passengers.

However, the thing they are curious about is not different from the scenery encountered when opening the cover of a deep freezer.

First of all, let’s explain some terms.

Dew point: Dew point is the temperature to which air must be cooled for water vapor in it to condense into dew or frost.

Condensation: Condensation is the psychial change of matter from gas into liquid.

The aircraft is pressurized with atmospheric air before takeoff. This atmospheric air taken from outside is warm and almost saturated with moisture and is very close to the dew point mentioned above.

After the first pressurization, the cold air blown by the air condition system cools the ventilation point areas. The invisible gas and water vapor in the region of sudden temperature drop turns into visible water droplets.

Since the air condition system blows the air at low pressures, this situation is observed only in the ventilation areas. If this air was blown at high flow rate and high pressure, this would appear in the whole cabin.

In addition, it is another curious issue that this incident is only in the early phasees of the operation and not seen in the ongoing flight phases.

To explain,

In the packs used for air conditioning, dry air is obtained by separating the air moisture. This is to prevent the structural elements against corrosion in the aircraft from effect of moisture.

At first, the moisture saturated air is taken back into the system from the dado panels. Dry air from the packs mixes in the mixer unit afterwards.

Now both the air inside the cabin has cooled and the air circulating inside is drier. In this way, the event no longer happens.

Yo can also look this quiz about air conditioning system.

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