One of the most useful things to know about liquid nitrogen is that it doesn’t want to be liquid. The concept is simple, nitrogen in its natural state is vapor and it is only through the application of technology do we render it into liquid. Therefore, the liquid nitrogen that comes in portable tanks is in a constant fight to return to its natural state.
Why is this important to understand?
As a cryotherapy business owner, liquid nitrogen is your number one variable expense, and at times can be a headache to manage. The tanks you use reduce the phase change from liquid to vapor by using a vacuum that keeps liquid nitrogen in its liquid state at a temperature of -321℉. However, tanks are not always able to keep it at this temperature, which is why you need pressure relief valves on tanks. The vessel has a finite amount of volume space for liquid and vapor, so as the liquid turns to vapor it increases the pressure in the vessel. Your tank will then release vapor to maintain the pressure in the vessel and reduce the volume of liquid in the tank. A typical 230L dewar can lose anywhere from 2-6% based on the volume size of the vessel, which is why bulk tanks are usually a more cost effective option for cryogenic users.
When using liquid nitrogen to operate cryotherapy chambers and saunas, the goal is to get liquid from your vessel to your chamber/sauna at the pressure required without losing liquid nitrogen, because nitrogen is money – and no one likes losing money. To achieve this, all the piping, hoses, and mechanical parts in the machine have to reach -321℉ before liquid reaches the system used to vaporize the liquid. This is why the first cooldown of the day takes the longest. This is also why it’s best to do subsequent sessions rather than spacing out sessions throughout the day. The longer the cool down takes, the more liquid nitrogen you use. This is why you see frost on a non-vacuum jacketed hose all the way from the vessel to the machine inlet.
With the above in mind, here are a few recommendations on how to conserve nitrogen, and subsequently stretch your dollar:
1. Use a Vacuum Jacketed Hose
Connect the nitrogen tank to your chamber or sauna using a vacuum jacketed hose to prevent frost and loss of nitrogen. This will reduce the amount of liquid that turns to vapor on the way to your chamber as jacketed housing is not as affected by outside temperatures.
2. Run Sessions as Close Together as Possible
The liquid in your hose will not remain that way if there is too much down time in between sessions. It will vaporize as the hose begins to warm up, especially in non-vacuum jacketed housing.
3. Refill Smaller Tanks Before They Empty
Keep your smaller tanks for cryo-facial and localized machines from becoming completely empty. An empty smaller vessel is not going to keep the temperature of nitrogen where it should be. Therefore you must use your liquid nitrogen to cool the smaller vessel before it starts to simply vaporize the liquid.
4. Use Your Nitrogen to Fill Larger Machines First
If you receive a typical 230L dewar, you should use the new tank to get as many cryotherapy sessions out of it as possible before using it to refill a smaller tank. As the liquid nitrogen decreases, the pressure inside the tank also decreases, meaning you may not have enough pressure to get the remaining nitrogen into a cryo chamber, but you will have enough pressure to get it into a smaller tank.
5. Remember That Liquid is Always a Disappearing Asset
Even with all the mitigation used in the vessels and the hosing, the liquid in your tank is always slowly disappearing. It does not sit in a tank like water. On average you will lose between 2-6% a day. By utilizing the above steps you will lower that percentage.