Creating a temperature differential on SF6 to evacuate a cylinder

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SUMMARY

The discussion focuses on transferring SF6 gas from one cylinder to another using a temperature differential method. The user has a 50KG cylinder containing 1-2LB of SF6 at 15PSI and aims to cool a second cylinder to -40C to facilitate the transfer. Initial calculations using the ideal gas law (PV=nRT) were attempted to determine the pressure differential, but the user realized that the compressibility of SF6 and the need for closed valves must be considered for accurate flow rate calculations.

PREREQUISITES
  • Understanding of the ideal gas law (PV=nRT)
  • Knowledge of compressible gas behavior
  • Familiarity with temperature differential methods in gas transfer
  • Basic principles of fluid dynamics
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  • Research the properties and behavior of SF6 gas under varying temperatures and pressures
  • Learn about flow rate calculations for compressible gases
  • Study the effects of valve configurations on gas transfer efficiency
  • Explore advanced gas transfer techniques using temperature differentials
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Engineers, physicists, and technicians involved in gas transfer operations, particularly those working with SF6 or similar gases in industrial applications.

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I have a 50KG cylinder with 1-2LB of SF6 at 15PSI. I want to transfer it into another cylinder by temperature differential.

Keeping it simple. I try to model it with two cylinders that has a valve on each cylinder. Connecting the cylinder with a 1/4" hose. Both valves are closed. The cylinder with the SF6 is at ambient temperature (25C). I cool the other cylinder to -40C (~-50C is solidifying point).. Open both valves.

How would I go about calculating the flow rate?

I try to find the pressure differential using ideal gas law

PV=nRT; P1/T1 = P2/T2, 15 PSI / 298.15K = P2/233.15K; P2 = 11.73PSI.

This is the wrong way since I know it is a compressible gas and the pressure should be much lower. Any help or direction would greatly be appreciated.

Thanks!
 
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Weird unit system :(.

PV=nRT takes compression into account, but you won't get a pressure difference if your valves are open. You just get a density difference, while the total amount of SF6 is constant (and known).

Your calculation would require the same amount of SF6 in both cylinders and closed valves.
 

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