superinsulsting cryo contaikners

In an ordinary glass thermos flask heat transfer from the hot or cold liquid takes place by conduction, convection and radiation. Heat is conducted by the neck of the thermos flak. Heat is lost by convection which is minimized by evacuating the system and radiation is controlled by giving a mirror finish to the outer wall of the inner vessel and inner wall of the outer vessel.In spite of these precautions heat is lost. These techniques are not effective if you have to store liquid nitrogen for prolonged periods. Liquid Nitrogen boils at -193 deg C.If the evaporation rate from the liquid Nitrogen container is 2 to 3 per cent per day conventional manufacturing techniques of glass thermos flask will not meet the evapolration rate as mentioned above. Hence an advanced manufatureing method is empolyed as described below.
A thin low thermal conductivity fiber glass tube is attached to to the inner aluminium shell by an epoxy resin capable of withstanding liquid nitrogen temperature. This fabrication method reduces conduction loss.
Multiple radiation shields reduce radiation loss. Multiple radiation shields consist of alternate layers of 5 micron polished aluminium strips 60 mm wide and low thermal conductivity cellulose paper wound on the inner shell in a pre determined fashion. The thickness of this blanket is determined by experimentation in a calorimeter to give minimum cold loss. A number of holes are punched through this blanket to allow air to escape during evacuation. The inner shell so prepared is connected to the outer shell by low thermal conductivity fiber glass tube.
Heat transfer through convection is reduced by evacuating the space between inner shell and the outer shell to a low vacuum of about 10 to the power minus 4 mm Hg.
A getter is used to take care of the out gassing that may occur during evacuation The entire assembly is heated from outside to aid degassing during evacuation.Evacuation may take one two days to reach the desired vacuum level. After checking the vacuum level heating is stopped and the container is allowed to come to room temperature. The container is checked for evaporation loss and the container is ready for dispatch to customer.