Liquid Nitrogen freezers used for maintaining cells in the gas phase of the nitrogen, must be designed to ensure that heat input from the access opening does not compromise the temperature at the top of the gradient.
In addition to the required insulating properties of the units, narrow access openings minimize warming during storage and retrieval activities.
The depth of liquid nitrogen in the freezer, in combination with the configuration of the unit, directly affects the working temperature in the gas phase. Less efficient units with larger openings require a greater depth of liquid to maintain adequate temperatures.
Inventory systems must be designed to ensure that all material remains at the desired storage temperature at all times. The material used to construct the inventory system can affect the operating temperature of the storage freezer. The two most common are aluminium and stainless steel. Each material has its advantages and disadvantages and the most important design criteria are material strength and thermal conductivity.
Stainless Steel provides an excellent design material for the construction of inventory racks but its low thermal conductivity limits heat transfer in a vessel. As a result stainless steel has a minimal effect on the natural gradient in a liquid nitrogen storage tank.
Aluminium has a high thermal coefficient when compared to stainless steel. Aluminium racks can often reduce the warmest temperature in a cryogenic freezer by 30ºC. Although they are not as durable as stainless steel, since they are a weaker material.
All liquid nitrogen storage tanks have a temperature gradient. They are coldest at the bottom (-196ºC). As temperatures are measured at increasing levels in the freezer, the temperature will increase. The rate of increase ie the gradient and the warmest temperature at the top of the tank varies with each unit.
We also have a full range of cryogenic boxes and labelling systems to store samples as low -196ºC
If you would like further information or a quote fill out the form below with the freezer/dewar make and model, internal dimensions and number of samples and we will do the rest for you.