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Volume correction due to temperature rise?
3

Volume correction due to temperature rise?

Volume correction due to temperature rise?

(OP)
Hi Guys,

I'll explain in detail... What I am doing is providing oil to an engine and then I want to measure the oil consumption. Prior to the test I will determine the volume1 and temperature1 (density1). After the test, I will determine the volume2 and temperature2 (density2). The problem is that the temperature at the beginning of the test is not the same as the temperature at the end of the test.

Can I use a simple relationship such as?

Actual Volume after test at initial temperature1 = Volume2 * (Density2/Density1)?

Basically I am converting my volume measured after the test to provide the volume at the initial density prior to the test so I can measure the actual consumption. I can't wait until the oil temperature to decrease, as this would cause too many delays.

Would this work?

Reference: http://www.osti.gov/bridge/purl.cover.jsp;jsessionid=2C1C53377CFEECAC11F489E7EC283E17?purl=/10179180-qGMb2h/

Thanks

Gabriel
 

RE: Volume correction due to temperature rise?

Look up Charles Law, and also be sure to check if pressure is constant, then you may remove it from the equation.

Also, if it's possible, you can always use the weight which is independent of temperature. But you have to be able to weigh it all.

Charlie
www.facsco.com

RE: Volume correction due to temperature rise?

Sure it would work.  At least, as well as the data you have (every measurement is, after all, another error source) and the validity of the temperature/density correlation you use to your particular oil, and the particular thermal expansion characteristics of your engine.  

Hint - you could calibrate the whole thing as a unit, with a fixed, known initial volume of oil, and vary the temperature...

 

RE: Volume correction due to temperature rise?

Doesn't Charles Law describe the behaviour of gases?

I've been playing with the equation that the OP proposed, and since Volume * density =mass, then dividing that mass at T2 by the density at T1 seems to give you a volume at T1.  I like it.

The change in density will be really small for the heat gain in an engine, but if that is the kind of precision your application requires, I'd say that your approach has a lot of merit.

David

RE: Volume correction due to temperature rise?

I was looking for those values earlier in the year for a hydraulic project I was working on.  You can usually find the bulk modulus (inverse of compressibility) reasonably easily for hydraulic oils at 60°F and atmospheric pressure.  Finding values for a rate of change with temperature proved impossible for my project.  Maybe there are other sources, but I couldn't find them.

David

RE: Volume correction due to temperature rise?

(OP)
Wow you guys are great ...

FACS - Yes charle's law is for gases and pressure is constant as my reservoir has a breather (therfore atmospheric pressure).

btrueblood - I like your hint and that is very logical, but would cost us more money to do as we would have to buy a heater. It would be the perfect method though!

zdas04 - I agree that the change will be very small. It's oil and the density (or specific weight) will vary between 58 and 60 lb/ft^3.

BigInch - I will check it out ... The coefficient of thermal expansion of my oil seems to be 0.00045 (avg. between -40 and +300 degF). Now I am unsure what to do with this number, but I will look it up.

Thanks a lot guys!!   

RE: Volume correction due to temperature rise?

(OP)
BigInch - I will stick to my original method, because we are actually losing volume as well because the engine is consumming oil, so the thermal expansion method will not work as wanted.

RE: Volume correction due to temperature rise?

providing the composition doesn't change (only temperature) the proposed rule should be true, i.e. at each temperature the oil has a certain density which you can measure, if the composition changes (with the same initial and final products) then it is still true at measured points, if composition is constant you could try to correlate densities or volumes with temperatures (with a linear or second order polinomial correlation) and in that case perhaps avoid measuring densities...

RE: Volume correction due to temperature rise?

A crazy idea from an old Sructural -

Run the engine up to operating temperature.  Drain the oil.  Load up your set volume.

Run engine back to opearting and then drain. Compare weigths/volumes

Will this work??

RE: Volume correction due to temperature rise?

Can you wait until the temper drops to the original starting temperature, and then measure the volume?
 

Charlie
www.facsco.com

RE: Volume correction due to temperature rise?

Pre-heat the oil before filling...

RE: Volume correction due to temperature rise?

(OP)
FACS - The simple answer is time is money, and it's a production facility that can't afford to wait around for 30 minutes or more...

1gibson - That's another possibility, but more costly for us.

With this, I'll stick to the original equation, and that will work well!!  

RE: Volume correction due to temperature rise?

I know Charles Law is for gasses, but if oil has a linear thermal expansion, wouldn't the formula be straight forward?

Just a thought.

I'm sure I saw a paper that taught this Law to students using oil. I could be wrong.

Charlie
www.facsco.com

RE: Volume correction due to temperature rise?

???  If you know the volume at Temp2, convert that back to the T1 reference and subtract.  That gives the volume used at the ref Temp1.  

α= linear coefficient of thermal expansion 1/F[&deg]

Change in volume = original vol x 3α /F[&deg] * (T2-T1)F[&deg]

 

"I am sure it can be done. I've seen it on the internet."  BigInch's favorite client.

"Being GREEN isn't easy." Kermitfrog http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.com

RE: Volume correction due to temperature rise?

(OP)
BigInch - ???  If you know the volume at Temp2, convert that back to the T1 reference and subtract.  That gives the volume used at the ref Temp1.

That's exactly what I will be doing, very simple!! smile

RE: Volume correction due to temperature rise?

galeblanc,

As already stated above by others, your approach will work pretty good.

Maybe this handy spreadsheet could help with tabulated values of lubricants density vs temperature

www.xlrotor.com/Lubricant_properties_calculator.XLS
 

RE: Volume correction due to temperature rise?

Why not weigh it?  Then you know how much mass you've lost regardless of what volume it wants to occupy.

RE: Volume correction due to temperature rise?

Gale,

There is an issue in timing for measuring the oil loss.  I.e. it takes a finite time, possibly many minutes, for the oil to drain back from galleries/heads into the sump before a volume measurement would stabilize.  The same issue presents for filling the engine, i.e. how fully drained was it before being filled, were dead spots that don't drain back (e.g. oil filter) already prefilled with oil.  Perhaps that is an issue that on a production line would be overcome by establishing a baseline measurement for a known "good" engine, provided the procedure is well controlled, and the drain-back time is not allowed to vary enough to scatter the measurement.

Weighing the engine would seem to be a good alternative.  There might be issues if some components off-gas or "burn in" and lose significant weight in the process.

Would oil loss not show up in exhaust diagnostics?

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