Cryogenic liquids are liquefied gases that are kept in their liquid state at very low temperatures. The word “cryogenic” means “producing, or related to, low temperatures,” and all cryogenic liquids are extremely cold. Cryogenic liquids have boiling points below -150°C (- 238°F) (Carbon Dioxide and Nitrous Oxide, which have slightly higher boiling points are sometimes included in this category). All cryogenic liquids are gases at normal temperatures and pressures. These gases must be cooled below room temperature before an increase in pressure can liquefy them. Different cryogens become liquids under different conditions of temperature and pressure, but all have two properties in common: they are extremely cold, and small amounts of liquid can expand into very large volumes of gas.
CRYOGENIC LIQUID PRODUCTS
- Carbon Dioxide
Cryogenic liquids are shipped and used in thermally insulated containers. These cryogenic liquid containers are specifically designed to withstand rapid temperature changes and extreme differences in temperature.
Liquid Dewar Flasks
Liquid Dewar flasks are non-pressurized, vacuum-jacketed vessels, somewhat like a “thermos bottle”. They should have a loose fitting cap or plug that prevents air and moisture from entering, yet allows excess pressure to vent. Flasks containing Helium, Hydrogen and other low-boiling liquids have an outer vessel of liquid Nitrogen for insulation.
Laboratory Liquid Dewar Flasks
Laboratory liquid dewars have wide-mouthed openings and do not have lids or covers. These small containers are primarily used in laboratories for temporary storage.
Liquid cylinders are pressurized containers specifically designed for cryogenic liquids. This type of container has valves for filling and dispensing the cryogenic liquid, and a pressure-control valve with a frangible (bursting) disk as backup protection. There are three major types of liquid cylinders, which are designed for dispensing:
- Liquid or gas
- Only gas
- Only liquid