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Find Pressure Increase for Mineral Oil due to change in Temp

thread135-474646

Find Pressure Increase for Mineral Oil due to change in Temp

Find Pressure Increase for Mineral Oil due to change in Temp

(OP)
Hi,

I'm working with a closed system full of mineral oil and the temp is increased from 25 C to 138 C. How do i calculate the increase in pressure due to the rise in temp? A physical experiment gave us a reading of 6,100 psi (42.06 Mpa) at 280 F (138 C) in a closed chamber with a pressure transducer but i cannot get the same number when trying to calculate this.

The parameters are,
- Coefficient of thermal expansion of mineral oil = 0.00064 1/C
- Initial Temp = 25 C
- Final Temp = 138 C
- Oil Volume = 4.430 Liters
- Bulk Modulus of Mineral Oil = 1.8 Gpa
- No change in volume

RE: Find Pressure Increase for Mineral Oil due to change in Temp

The normal boiling point of mineral oil is about 310o C, so the vapor pressure of mineral oil at 138o C is negligible when compared to the total pressure of 6,100 psi.

It's all about liquid expansion. What was the pressure at 25o C?

Good Luck,
Latexman

RE: Find Pressure Increase for Mineral Oil due to change in Temp

(OP)
The test started at 25 C. Mineral oil at 25 C was placed in a test chamber that was completely sealed off and a pressure transducer was connected to get a pressure read out as the temperature was ramped up to 138 C.

RE: Find Pressure Increase for Mineral Oil due to change in Temp

You cannot get any answer with the data provided. What is the chamber material? What is the wall thickness? What is it's modulus?

Why do any calculation, when all that is needed to prevent any significant pressure increase is a few dozen milliliters of nitrogen (or vacuum) somewhere in the chamber or instrumentation tubing?

Did you know the pressure rating of the chamber before your experiment and take the precautions needed for if, or when, it exploded?

RE: Find Pressure Increase for Mineral Oil due to change in Temp

Well you don't appear to have allowed for expansion of the vessel / chamber either under temperature expansion or pressure expansion.

To say the volume does not change is correct in a macro sense, but incorrect when you're operating at such small changes in volume.

So theoretical pressure based on absolutely no expansion of the vessel gets you about 130 Mpa. You have 42 (answer to life the universe and everything). Not too far adrift.

https://www.theguardian.com/books/2011/feb/03/doug...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Find Pressure Increase for Mineral Oil due to change in Temp

Quote (nhm4196)

The test started at 25 C. Mineral oil at 25 C was placed in a test chamber that was completely sealed off and a pressure transducer was connected to get a pressure read out as the temperature was ramped up to 138 C.

That's a non-answer.

Good Luck,
Latexman

RE: Find Pressure Increase for Mineral Oil due to change in Temp

Have you had a chance of comparing your results to a Mollier diagram of the mineral oil? about the calibration of the pressure transducer was that done?

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