Definition
A double-walled container with a vacuum between the walls, used to store extremely cold liquids such as liquid oxygen or liquid nitrogen at low pressure. The vacuum gap minimizes heat transfer, slowing the rate at which the liquid warms and boils off into gas.
Plain English
A specialized insulated flask that keeps very cold liquids cold for a long time by surrounding the inner container with a vacuum, which blocks heat from getting in.
Context Anchor
Seen in aircraft oxygen-system maintenance, especially when discussing liquid oxygen storage, servicing, or handling equipment.
Derivation
Named after Sir James Dewar, the Scottish chemist who invented the vacuum flask in 1892 while researching the liquefaction of gases. The household 'Thermos' is the same basic invention, commercialized later.
Why Pilots Care
Liquid oxygen is stored and serviced in Dewar bottles. A damaged or contaminated Dewar can lose its vacuum, causing rapid boil-off and dangerous pressure buildup. Technicians must handle them carefully and inspect them per the maintenance manual.
Analogy
Think of a high-end Thermos flask. The principle is identical -- two walls with a vacuum between them -- just built to industrial standards for cryogenic liquids.
Intuition Check
Do not read “bottle” as an ordinary container here. A Dewar bottle is a specially insulated container for extremely cold liquids, not a simple storage bottle.
Example Sentence 1
The technician transferred liquid oxygen from the storage Dewar bottle into the aircraft's converter unit.
Example Sentence 2
A Dewar bottle kept the cryogenic fluid stable while it was transported across the ramp to the maintenance hangar.