Decreasing value of interfacial tension

[EricGoetz92]

So a practice question reads:

"What would a decreasing value of interfacial tension indicate?"

My answer was contaminants and in the the Paul Gill book it states that "It has been established that an IFT of less than 15 dyn/cm almost invariably shows sludging."

So are "contaminants" and "sludging" different, is the Gill book wrong, or is the test question incorrect/written poorly? What is the correct answer?

[storm89]

So a practice question reads:

"What would a decreasing value of interfacial tension indicate?"

My answer was contaminants and in the the Paul Gill book it states that "It has been established that an IFT of less than 15 dyn/cm almost invariably shows sludging."

So are "contaminants" and "sludging" different, is the Gill book wrong, or is the test question incorrect/written poorly? What is the correct answer?

What were the other answer options presented?

[EricGoetz92]

What were the other answer options presented?

I wish I had taken a screenshot of them, but I didn't. I think water/moisture might have also been an option. At the time, it seemed pretty cut and dry that it would be contaminants so I didn't screenshot it. What else do you think it could be? I am mainly a P&C guy, so oil samples aren't my strong suit, but even now when I look up more stuff about it, the main focus seems to be sludge build up (I'm pretty sure "sludge" wasn't explicitly an option). Are sludge and contaminants different? If deterioration was an option, would that be a better choice?

[storm89]

I wish I had taken a screenshot of them, but I didn't. I think water/moisture might have also been an option. At the time, it seemed pretty cut and dry that it would be contaminants so I didn't screenshot it. What else do you think it could be? I am mainly a P&C guy, so oil samples aren't my strong suit, but even now when I look up more stuff about it, the main focus seems to be sludge build up (I'm pretty sure "sludge" wasn't explicitly an option). Are sludge and contaminants different? If deterioration was an option, would that be a better choice?


I think sludging and contamination refers to separate issues. Without knowing the other choices it's hard to say what the best answer is but I found this link which says "changes in an oil’s surface tension to be the earliest sign of contamination, sludge potential and oxidation."

https://www.machinerylubrication.com/Read/376/surface-tension-test

Contamination, sludging, and oxidation could all be correct I think.

[sparky2005]

Thank you, that article was very helpful

[brandonbreon]

The question/answers were:

What would a decreasing value of interfacial tension indicate?

a. Contaminants
b. Oxidation by-products
c. Neither
d. Both

[Kalbi_Rob]

The question/answers were:

What would a decreasing value of interfacial tension indicate?

a. Contaminants
b. Oxidation by-products
c. Neither
d. Both

I would say both as this would introduce contaminants and increase the possibility of sludge(a Oxidation by-product). Below is a quote from a white paper on Transformer Interfacial tension:
https://www.satcs.co.za/Interfacial_Tension-IARGray2007.pdf

Significance:
The magnitude of the IFT is inversely related to the concentration of the hydrophilic degradation products from the deterioration of the oil. Since the hydrophilic materials are usually highly polar and thus not very soluble in the non-polar oil, the presence of these species can result in sludge formation. These materials that remain dissolved in the oil can affect the desired electrical properties of the oil. They will reduce the dielectric strength and increase the dissipation factor of the oil. Sludge build-up can also affect the heat transfer characteristics of the oil by slowing or perhaps even blocking circulation of the oil. There is usually an inverse relationship between the neutralization number of an oil and its IFT. As an oil sample undergoes oxidative degradation, its neutralization number will increase while its IFT value will decrease. It should also be recognized that a decrease in the IFT does not imply that the acidity must also be high, since there are other non-acidic contaminants that could be present in the oil that are hydrophilic and will lower the IFT but not raise the acidity. An example of such a situation might be that of a free breathing transformer near salt water where a salt-water mist might be able to enter the unit. Such an event will not affect the acidity but would markedly affect the IFT and dielectric strength of the oil. The IEEE has suggested guidelines for IFT values depending on the type of oil and the unit it is being used in (IEEE C57.106-1991)