Questions about carbon dioxide gas cylinders
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In my work, I encountered a situation where carbon dioxide cylinders were filled with liquid nitrogen dioxide. During the production process, these cylinders were heated using a water bath at a temperature of 40 degrees. What is the phase state of carbon dioxide inside the cylinders at this temperature: liquid, gas, or a mixture of both? The critical temperature of carbon dioxide is 31 degrees, and the critical pressure is a little over 7 MPa. My understanding is that when the heating temperature reaches 40 degrees, which is above the critical temperature of carbon dioxide, no amount of pressure can turn the carbon dioxide cylinder into a liquid state. The carbon dioxide inside the cylinder should be in gaseous form, and the pressure within the cylinder is very high; if the cylinder’s strength is insufficient, a physical explosion of the cylinder may occur. I would appreciate some advice from the experts, thank you!
It may be in a supercritical state, that is, it is neither a liquid nor a gas, with a density similar to that of a liquid and a viscosity similar to that of a gas.
I also considered supercritical fluids, when the temperature and pressure inside a carbon dioxide cylinder exceed the critical temperature and critical pressure. But it is unclear whether it belongs to supercritical fluids
The water temperature is 40 degrees, while the temperature of the medium inside is much lower than 40 degrees.
It’s absolutely wrong to do so; gas cylinders must not be heated directly. After the carbon dioxide is discharged from the cylinder under reduced pressure, it’s possible to use a coiled tube immersed in hot water; moreover, since the latent heat of vaporization of carbon dioxide is not high, a longer pipe together with fins is generally sufficient for vaporization.
Thank you all, I’ve learned a lot! :)
I don’t think there’s any danger. The methods for liquefying gases are either by applying pressure or by lowering the temperature. In the case of carbon dioxide cylinders, liquefaction is definitely achieved through pressure; the design temperature is at least 50 degrees, so there should be no problems with gasification using this method. Personal understanding
@jl_xu: Gas cylinders cannot be heated directly. Which standard states this? Could you tell me? I couldn’t find it
What exactly did the original poster reinstall? Carbon dioxide? Nitrogen dioxide?