Pressure in a half-full vessel filled with olive oil@330F 1

[webpine]

Hello,

we are planning to do some test to see the high temperature performance of a device. To do it, we need to fill an small aluminum tube (ID 2.5", 25" long) with olive oil to about half of its volume, and then put the tube in oven to heat it up to 330 degree fahrenheit. The tube is sealed with oring.

We know the expansion of this oil will about 10%. Olive oil has boiling temp 570F, smoke point 470F. The question is

1. How high the pressure will build up in the tube at 330F?

2. We certainly do not want any smoke (or fire!) since it will ruin the oven (expensive one!). Any issue you see with the plan?

Thanks!

 

[boo1]

The pressure change will be caused by the change in volume caused by the temperature differential in the vessel and oil, and the increase gas temperature.

Consider aproximation using a summarion of the 3
Thermal growth change in the cylinder reduces volume
Oil displacement ~10%
Ideal gas law PV=nRT

 

[AllHandlesTaken]

Boo1 - if I am reading your statement correctly "Thermal growth change in the cylinder reduces volume" - that is not correct. The cylinder diameters (both ID & OD) INCREASE - so the volume will increase.

The easiest (if the information is available) answer is - the pressure inside the cylinder will be equal to the vapor pressure of your olive oil @ 330F

 

[StevenHPerry]

At 330°F, your 25" long tube will be 0.09 inches longer than at room temp. It doesn't sound like this testing is done to that degree of precision though.

I'm not immediately understanding AllHandlesTaken claim that the pressure will be the vapor pressure of olive oil at 330F. If olive oil has a boiling point of 570F, the vapor pressure at 330 must be less than 1 atm. Since the other half of the cylinder's volume, I assume, contained air at 1atm when the cylinder was sealed, the pressure would have to increase above 1atm, not decrease.

I would ignore both the thermal expansion of the cylinder and the olive oil's density change and just do ideal gas law on the air. That will get you close enough.

As for #2, I would have a large drop pan isolating any leaks from the heat source.

 

[AllHandlesTaken]

StevenHPerry, yes I was a little too quick with my reponse - I was thinking of pressurized CO2/propane containers, and now I am confused because, as you pointed out 330F is not even above the boiling point of olive oil at 1 atm .............. my brain is all fuddled now ........ coffee time

 

[desertfox]

Hi webpine

According to my calculations just concentrating on the air thats left in the vessel and forgetting that the tube expands for the minute then the pressure of the air at 330F
would be 1.5 times atmospheric ie from the law:-

P1/T1 =P2/T2

desertfox

 

[desertfox]

Hi again

Sorry should have mentioned once you have this pressure you need to check hoop stress in your cylinder as you haven't stated the wall thickness.

desertfox

 

[BigInch]

The total pressure inside the cylinder will equal the partial pressure of the olive oil plus the partial pressure of any remaining air. The partial pressure of the olive oil, will be the vapor pressure of olive oil at 330 F, assuming the air space is saturated with olive oil.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[racookpe1978]

But, why pressurize with olive oil at all? If the final "test" is going to be so low, why not just use an air test up to 45 psig (3x atmosphere?) - if you're worried about leaks.

 

[BigInch]

Don't you think its probably some kind of olive oil experiment, rather than a pressure test of the cylinder.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[moltenmetal]

I could have sworn I posted a reply to this! Where'd it go?

If the oil has never been heated before, it may contain some water. The boiling and smoke pont measurements are short of what you really need, which is the vapor pressure of the fresh oil at 330 F. How much water and how much air are in there will determine the pressure in a cylinder which is heated to final temperature while remaining closed.

 

[BigInch]

Don't know, but I think we already finished this one off.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/