Cryogenic Liquid Nitrogen Dewars

In recent weeks, an issue has been discovered regarding the Lab 20 discharge device. The rubber plug on the device has been found to not create a complete seal, thus hindering the pressure building process required for proper liquid withdrawal. This problem arose from a change in material from our supplier and only effects Lab 20 discharge devices. Engineering has come up with a fix for this problem which involves switching out the rubber plug and bolt on the discharge device. If your customer is experiencing trouble with their Lab 20 discharge device, you will need to order the modified plug (13465974) and the new bolt assembly (9086779).

Q: Will the temperature inside the dry shipper exceed -135°C at any time during flight when the dry shipper is located in an unpressurized cabin such as the cargo area as opposed to the passenger cabin?

A: There will be an increase in evaporation during ascent and a decrease during descent while the liquid changes its saturation pressure. Assuming that the shipper does not run dry, which is unlikely if properly charged, the temperature should be essentially unaffected by the entire process. If anything the temperature will drop lower than normal during ascent and stay approximately normal during descent.

Q: By adding 6 more racks would the evaporation rate lower.

A: No. If anything the evaporation rate would increase since additional racks add more heat transfer paths to the LN2. This effect would be especially obvious if using aluminum racks since they offer much better thermal conductivity than stainless steel. With stainless steel racks, the effect on evaporation rate would be minimal. The positive side of this is that increased evaporation leads to lower vapor temperatures, meaning that adding aluminum racks gives the user better sample security at the expense of higher liquid usage.

Q: Would a newly built unit have the same temperature profile as one with the retrofit sleeve?

A: A unit with annular aluminum would have s similar temperature profile, but not necessarily the same profiled as the retrofit sleeve. The retrofit sleeve does not put any aluminum below the LN2 surface with normal vapor storage level settings. Thus it just moderates the gradient of the vapor above the liquid. The annular aluminum extends to the bottom of the inner shell, adding some heat to the liquid to increase convection. The consumption impact is minimized because the SS shell slows the conduction of heat from the aluminum to the liquid as compared to what it would be if the aluminum were in the storage chamber with the bottom submerged in liquid.