Calculations Help: Working Out SF6 Usage in Litres

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Discussion Overview

The discussion revolves around calculating the volume of SF6 gas used in a 67.4 litre vessel filled to a pressure of 6 Bar. Participants explore the relationship between pressure, temperature, and density of SF6, and whether the usage should be expressed in litres or weight.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Homework-related

Main Points Raised

  • One participant seeks assistance in determining the volume of SF6 used in litres for a specific pressure and vessel size.
  • Another participant offers to provide the density of SF6, contingent on knowing the temperature and confirming that the pressure is gauge pressure.
  • A participant confirms the temperature as approximately 20 degrees Celsius and states that the pressure is measured with a gauge.
  • At the specified conditions of 6 barg and 20 degrees Celsius, a participant calculates the density of SF6 to be roughly 46.5 kg/m3 and notes that the gas is superheated.
  • There is uncertainty expressed regarding the conversion of gas volume to litres, with a suggestion that the inquiry might pertain to liquid SF6 and a need to clarify the conditions of any liquid source.

Areas of Agreement / Disagreement

Participants have not reached a consensus on how to calculate the SF6 usage in litres, and there are competing views on whether the question pertains to gas or liquid SF6.

Contextual Notes

Participants note the importance of temperature and pressure definitions, as well as the distinction between gauge and absolute pressure, which may affect the calculations. There is also a mention of saturation temperatures relevant to the state of SF6.

Scara
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Hi Folks,

Not the best at this so hoping somebidy can help me.

I have a 67.4 litre vessel and I'm filling it with SF6 to 6Bar. Can I work out how much SF6 I'm using in litres?

Is this a dumb question? should nI be asking what weight I'm using.

I've been asked to supply usage in litres.
 
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Hi Scara. I can give you the density of SF6 if you can provide the temperature and verify the pressure is gage and not absolute pressure.
 
The sf 6 is at room temperature around 20deg Celsius . Pressure measured on vessel with gage.
 
At 6 barg and 20 C, density is roughly 46.5 kg/m3. The saturation temperature at this pressure is -19 C and at atmospheric pressure the saturation temperature is -68 C.

So at this pressure and temperature, you have a superheated gas. I'm not sure why or how you could put that into liters, but I wonder if there is a liquid source and you're being asked to determine how many liquid liters are needed for this 64.7 L vessel, in which case you need to define the conditions of the liquid source.
 

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