What Is Vessel Inventory And Why Is It So Important?

When working with cryo technology, risks are always present. This is because to achieve a status of cryopreservation, temperatures need to be extreme. Indeed, they go so low below zero that tampering with liquid nitrogen is just as dangerous as handling liquid metal.

Most people remember that epic scene in Terminator 2 when T1000 is frozen to the core by liquid nitrogen. If that happens to a human, the results can be terrible. Hence, a proper inventory minimizes the chances of accidents and protects cryogenic equipment as well.

Liquid Nitrogen Freezers

Liquid Nitrogen Freezers are the perfect way to store cryogenic samples inside a properly-labeled cryo box with a grid. Beyond the organizing options, the cryo box offers an external inventory system that needs implementation. This is because you can’t dive into a liquid nitrogen freezer to find the sample you’re looking for. Moreover, the interaction time between your body and the extra-low temperatures needs minimizing at all times.

Efficiency Matters & Time Counts

A wide variety of liquid nitrogen freezers are available in the market. They need to have liquid nitrogen on the bottom and a gas phase naturally generated on the top. As efficiency and time play a key role in maintaining the needed temperature (-190°C to -120°C) going in and out of the freezer needs to be an expedited circumstance. In this vein, a proper inventory will allow the technician to find the needed sample in a smaller time frame.

Some considerations to bear in mind:

• Access – Usually, the access to a liquid nitrogen freezer is very narrow to avoid warmer outside temperatures from changing the internal one, and thus, breaking the cryogenic cycle.
• Liquid Depth – On less-efficient liquid nitrogen freezers with wider openings, the liquid phase needs to have a larger depth to accommodate more liquid that will maintain a gas phase for longer at adequate temperatures.
• The Material Of The Inventory Matters – Since everything needs to remain at extreme temperatures, the material from which the cryo box (or another organizer) needs close examination. In this sense, each material generates a specific reaction.

Material Strength & Thermal Conductivity

Different materials have distinct thermal conductivity. For example, a very common material is stainless steel. Its use is very common due to two main characteristics: it features minimal thermal conductivity which limits heat transfer in a vessel.  As a result, when introduced or removed from a nitrogen tank, the effect is minimal.

In comparison, a different material like aluminum generates a bigger disparity inside the vessel when it is in or out of it. To put it in numbers, an aluminum rack can reduce the warmest temperatures in a liquid nitrogen freezer by as much as 30°C. Also, aluminum is a weaker material than stainless steel which makes it not as durable or reliable.

Temperature Gradient

All liquid nitrogen storage units feature a temperature gradient that usually starts as low as -196°C and goes up as you move from the liquid bottom to the gas phase. In this sense, a cryo box, for example, usually resists up to -191°C. Thus, we should store it within the gas phase without touching the liquid nitrogen to avoid ruining its structure and functionality.

Why Is The Vessel Inventory So Important?

Without proper vessel inventory, all efforts to keep samples in cryogenic temperatures would be lost. There is currently no apparatus that can make cryogenic storage a simple, non-dangerous endeavor. Thus, if vessel inventory is well done, chances are professionals will always find the samples without breaking the cryogenic ecosystem.