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Physics
Classical Physics
Thermodynamics
Calculating Cooling Effect in Gas Cylinder Expansion
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[QUOTE="OG63, post: 6602598, member: 699050"] I'm building a gas supply system that will dump half the contents of a compressed gas cylinder of nitrogen in 10 minutes. I need to ensure the output delivery pressure doesn't fall below a certain limit because of cooling during the gas expansion. If the cooling effect is excessive, I will need to heat the cylinder to compensate for it and prevent excessive pressure drop. But if the cooling effect is relatively small, the thermal mass of the steel cylinder might be sufficient to prevent excessive cooling of the contents in the 10-minute time frame that matters. (I'm hoping for the latter, of course.) Cylinder volume: 49.3 L Initial cylinder pressure: 1250 psi Final cylinder pressure: 625 psi Initial cylinder temperature: 20 C Final cylinder temperature: ? Cylinder weight: 42 kg Cylinder material: steel I've included the cylinder weight and material for anybody who wants to look at the entire system. However, since this is a risk mitigation exercise, I'm willing to make any sort of simplifying assumptions that lead to a "worst-case scenario" answer for the gas alone (i.e., the maximum possible cooling). For what its worth, I tried using an online thermodynamic calculator but got hung up when I couldn't decide what type of process this was. In one sense, it seems like an isochoric process (constant volume) because the cylinder volume doesn't change. But that didn't seem right because the volume of the initial gas charge certainly changed when half of it expanded into the open atmosphere. I also considered solving this as an isothermal process problem, with the idea that I might be able to calculate the amount of energy required to keep the temperature constant. But here again, I'm tripped up by the question of whether I should consider the system to be the initial amount of gas in the cylinder or just the half that's left in the bottle after dumping. I should have paid more attention in Physics class, and so now must humbly request assistance from those who did. [/QUOTE]
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Thermodynamics
Calculating Cooling Effect in Gas Cylinder Expansion
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