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Re: VII (VM), shear, base-oil viscosity, HTHSV, friction, and wear: State of the art [Re: Gokhan] #5130739 06/10/19 08:07 PM
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Originally Posted by Gokhan
That said, to answer your questions, this is what they said about temporary shear of the VIIs (VMs), which I already quoted in my summary of the paper: "Temporary shear thinning is generally believed to result from conformational changes, such as partial alignment of the VM polymer molecules in solution under shear, that reduce the interactions between solvent/polymer and polymer/polymer molecules and thus the blend viscosity. The low shear rate viscosity is recovered fully after cessation of shear."

According to what they are saying, when the shear rate becomes very high, these interactions become so weak that the VIIs no longer contribute to the viscosity. Of course, they don't go anywhere -- the loss of interaction is due to their alignment under shear.


This link talks about that in Figure 2, and the text about Figure 2 on page 39. And this was back in 2004.

https://www.stle.org/images/pdf/STL...20and%20Friction_tlt%20article_Oct04.pdf

Re: VII (VM), shear, base-oil viscosity, HTHSV, friction, and wear: State of the art [Re: Gokhan] #5133413 06/13/19 05:30 PM
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Gokhan Offline OP
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Here is the theory behind my HTFS formula:

[Linked Image]
[Linked Image]

The average error in HTFS for different VII types is only 6%.

However, I didn't study the error in ASTM D341 and density extrapolation, as the paper had the dynamic-viscosity values directly but not the density values.

Here is the comparison of my formula to the test oils in the paper. The oil (type of the base oil, DI, and VII) is described in the first column. I couldn't compare most DI-containing oils except Oil #11 because they didn't have high-temperature data on them.

Note that the DI (detergent inhibitor) package shears as well, in some case substantially. As a result, in the second Newtonian phase (ultrahigh shear rates, full temporary shear), you're left with the base oil + unsheared part of the DI + VII solvent but the VII polymer has no effect.

PMA VII is unusual in that the viscosity-boost rate increases with the temperature, greatly enhancing the viscosity index (VI). Some ultrahigh-viscosity-index 0W-20 oils may be using a PMA VII. The downside is that it requires a lot more polymer than other VII types, which could increase the deposit formation. Nevertheless, the formula still works for the PMA VII, as far as HTFS is concerned. Note that the calculation of the VI, which is a secondary calculation, is not accurate, especially for VIIs with a strongly temperature-dependent viscosity-boost rate.

[Linked Image]

https://docs.google.com/spreadsheets/d/1gnOrQxsbymULx1s6_uBQi8zNHfJXg7lwwQpwzLSIWQI/edit?usp=sharing


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Re: VII (VM), shear, base-oil viscosity, HTHSV, friction, and wear: State of the art [Re: Gokhan] #5140578 06/22/19 12:49 AM
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Gokhan Offline OP
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This is the summary of how key viscosity quantities relate to the VII content:

L = low-shear (HTLS) viscosity
H = high-shear (HTHS) viscosity
F = full-shear (HTFS) viscosity (base oil and sheared additives)
V = VII content
A = A_Harman index
b = VII viscosity-boost rate ~ 10.5 (typical value but varies)
s = VII temporary-shear rate ~ 2.0 (typical value but varies)
c = b/s ~ 5.25 (typical value but varies)

A = H/L

V = (1/s) * (1 - A) = (1/s) * (1 - H/L)

L/F - 1 = c * (1 - A) = (b/s) * (1 - A) = (b/s) * (1 - H/L) = b * V

L/F - 1 represents how pronounced the non-Newtonian (S-shaped region) is. When it gets higher (the S-shaped region in the curve gets deeper), the fuel economy may improve but the wear may increase.

[Linked Image]

Also:

1 - A = 1 - H/L = s * V

1 - A represents how much the oil shears at 10^6 1/s, which is the shear rate at which the HTHS viscosity is measured. When it gets higher, the high-shear (HTHS) viscosity gets lower with respect to the low-shear (HTLS) viscosity. It is directly related to the VII content and how much the VII temporarily shears at the 10^6 1/s shear rate. Note that part of the additive package temporarily shears as well, appearing as a VII even if the oil is a monograde with no VII but only an additive (detergent inhibitor [DI]) package.

In addition:

H/F = (1 + b * V) * (1 - s * V)

Here is a plot of H/F as a function of V (HTHS/base-oil viscosity @ 150 °C as a function the VII content). Note that the VII content is in arbitrary units, as the commercially solved VII comes in various solvents and also the actual treat rate depends on the VII type. Nevertheless, the range of HTHS/HTFS in the plot (1.00 - 1.80) represents the range for most commercial oils and the shape of the curve should be similar for other b and s values:

[Linked Image]


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