Small liquid nitrogen freezers are used in research laboratories, biobanks, and other scientific settings for cryogenic storage of biological specimens. These freezers are designed to maintain a temperature of -196°C (-320.8°F) using liquid nitrogen (LN2) as a coolant. One important factor to consider when using a small liquid nitrogen freezer is the evaporation rates of LN2. Evaporation rates determines how often the freezer needs to be refilled with LN2. Evaporation rates are typically measured in two ways: static evaporation rates (or Static Hold Times) and evaporation rates under normal working conditions. You will typically find both attributes listed on the specifications sheet of the product, but they are often misunderstood. Explained below are the differences between static evaporation rates and evaporation rates under normal working conditions.
Static Evaporation Rates (Static Hold Times)
Static Evaporation Rates, or Static Hold Times, refer to the amount of time a tank can remain in a “static setting”. A “static setting” simply means the tanks were left undisturbed and without any lid openings for a set period of time. This is typically measured in days or weeks. However, it’s important to note that small liquid nitrogen freezers are rarely used in a static setting. Therefore, these rates are only intended to be used as general estimates.
The actual evaporation rate can vary depending on a variety of factors. These factors include temperature, atmospheric pressure, container history, manufacturing tolerances, and individual patterns of use. For instance, if a liquid withdrawal device is installed there is an increase in the static evaporation rates. The evaporation rate will increase by an estimated factor of 2.33 in this situation. To show an example of how this is calculated, lets say you have a tank with a static evaporation rate of 0.18 liters per day. If a liquid withdrawal device is installed, it would be 0.18 x 2.33 which would equal 0.42 liters per day (estimated only). Keep in mind that these are only estimates due to each facility’s unique environmental and usage factors.
Evaporation Rates Under Normal Working Conditions
Evaporation Rates, or Normal Working Duration, refer to the estimated container performance when opened 2-3 times a day under normal operating conditions. This number is typically about 60-70% of the static evaporation rate but will vary depending on actual usage. Actual working time may vary due to current atmospheric conditions, container history, manufacturing tolerances, and individual patterns of use.
To ensure optimal conditions for the longevity of the LN2 freezer, it’s important to replace the lid and racks/canisters/samples as soon as possible. Leaving the lid off the unit for an extended period of time or introducing warm racks into the tank can cause the LN2 to evaporate at a faster rate, reducing the working duration of the freezer. It’s also important to note that the introduction of warm racks or samples into the LN2 freezer can cause the LN2 to evaporate at a faster rate. The temperature of LN2 is -196°C (-320.8°F), so introducing room temperature racks or samples into an LN2 freezer can burn off a lot of LN2 trying to cool them down to these extreme temperatures.
In conclusion, small liquid nitrogen freezers are essential tools for long-term storage of biological specimens in scientific settings. Understanding the meaning of evaporation rates of LN2 and taking steps to optimize conditions can help maximize the working duration of the freezer and ensure the safe storage of valuable biological samples. Follow the links for more information on LN2 Cryogenic storage, Liquid Nitrogen Dewars | LN2 Dewars | Cryogenic Storage Dewars | MVE (labrepco.com), LN2 Freezers, Cryogenic Shippers or contact us today to speak with a LabRepCo area rep.