A dewar flask is a vacuum-jacketed insulating vessel originally designed by Sir James Dewar in the late nineteenth century to store cryogenic liquids by minimising heat transfer through the vessel wall. The vacuum layer between the inner and outer walls eliminates conductive and convective heat transfer, while a reflective inner surface reduces radiative heat gain. In modern laboratory use, the term dewar flask most commonly refers to open-necked vessels ranging from 1 to 50 litres used for liquid nitrogen dispensing, sample cooling, and short-term biological material handling.
A nitrogen storage tank used in an IVF laboratory differs from a working dewar flask in several important respects. Storage tanks are engineered for continuous unattended long-term operation with very low daily liquid nitrogen evaporation rates, compared with open-necked working dewars which may evaporate liquid nitrogen at significantly higher rates depending on neck diameter and ambient conditions. Storage tanks incorporate narrow-neck designs that minimise surface evaporation, accept internal racking and canister systems for sample organisation, and are typically fitted with liquid nitrogen level monitoring connections.
In an IVF laboratory, working dewar flasks serve as temporary transfer vessels for moving liquid nitrogen between the bulk storage tank and the vitrification workstation, and for short-duration cooling tasks such as plunging vitrification devices or maintaining goblets during loading. The primary sample repository function is performed exclusively by purpose-built nitrogen storage tanks. Cryolab supplies both working dewar flasks and long-term nitrogen storage tanks to fertility clinics across the UK. The full range is at cryolab.co.uk/storage-vessels/.
