Thermodynamics question: venting a tank of liquid oxygen

• msteves
In summary, the conversation is discussing the process of subcooling a dewar of liquid oxygen by releasing the pressure on top of it. The liquid oxygen is initially at -297.33 F and is pressurized to 3 psig before being allowed to reach thermal equilibrium. The question is how much of a temperature drop can be expected when the pressure is released. The total mass of liquid oxygen is 68,000 kg and the final pressure is 0 psig. The speaker is unsure of which equations to use to calculate the temperature change. Another person suggests that there may be another factor at play that the speaker is not aware of.
msteves
I am trying to figure out how you can subcool a dewar of liquid oxygen (vacuum insulated) just by releasing the pressure sitting on top of it. The liquid I am thinking of in this case is liquid oxygen, which boils at -297.33 F at 1 atm. Let's say I fill a dewar with LO2, then pressurize that dewar to 3 psig (using cold gaseous oxygen), and then let it reach thermal equilibrium. Now once I open to vent to let that gas on top of it vent to atmosphere, there should be adiabatic expansion of the liquid of the pressure decreases, which should then decrease the temperature. All I am trying to figure out is about how much of a temperature drop would be reasonable to expect by doing this.

Some conditions:
Total LO2 mass = 68,000 kg
P_initial = 3 psig = 17.7 psia
P_final = 0 psig - 14.7 psia
T_initial = let's say -297 F
T_final = ?

I assume I can use the pressure change to somehow figure out the density difference, but I haven't taken thermodynamics in a while, so I am stuck on which equations/assumptions to use.

Thanks for the help.

The energy in compression and expansion of liquid is minuscule and in any case if you pressurize it it will boil at a higher temperature, so you won't gain anything.

Thanks, that's in line with what I was thinking at first. In my particular example, there must be something else going on that I am unaware of.

1. What is thermodynamics?

Thermodynamics is a branch of physics that deals with the relationships between heat, energy, and work. It studies how energy is transferred and transformed between different forms, such as heat and work.

2. What is liquid oxygen?

Liquid oxygen is a highly concentrated form of oxygen that is kept at extremely low temperatures (-297°F or -183°C) to maintain its liquid state. It is commonly used as a rocket propellant and in medical applications.

3. Why is it important to vent a tank of liquid oxygen?

Venting a tank of liquid oxygen is important because it prevents the buildup of pressure that could cause the tank to rupture or explode. It also ensures that the oxygen is kept at the correct temperature and pressure for its intended use.

4. How is a tank of liquid oxygen vented?

A tank of liquid oxygen can be vented by opening a valve on the tank that allows the oxygen to escape into the atmosphere. This can also be done through a controlled release system that regulates the rate at which the oxygen is vented.

5. What safety precautions should be taken when venting a tank of liquid oxygen?

When venting a tank of liquid oxygen, it is important to follow proper safety protocols to avoid any potential hazards. This includes wearing appropriate protective gear, ensuring proper ventilation in the area, and being aware of the possibility of fire or explosion. It is also important to follow the manufacturer's instructions and guidelines for handling and venting liquid oxygen.

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