which equation does widman calculator use?

[lipadj46]

I see the widman viscosity calculator used around here for proving what oil is thinner at a specific temperature etc. I know widman was active at one point on this site. At any point did he say what equation he uses in his calculator? From reading a couple textbooks I see that the vogel equation is the most accurate but requires 3 known viscosity measurements and I know the widman requires 2 data points. Maybe it is just table driven? Anyone recall or have enough time on their hands to search?

 

[jstutz]

ASTM D341. 3 is the equation that i believe they use. There is a .ppt here that explains the equation. www.viscoanalyser.com/ASTM.ppt

I have worked thru the math and created an excel spreadsheet that matches very well to widman it is here https://docs.google.com/leaf?id=0B6pXF6f...2ZDVk&hl=en

If you have any questions about the math or the spreadsheet, just shoot me an email [email protected], or PM me.

 

[lipadj46]

That is the walther formula, cool thanks. That is less accurate than the vogel formula though I'm not sure by how much or at what extremes they start to diverge.

 

[Gary Allan]

flatlander here

Can you even use the HTHS visc as your 3rd POR? Otherwise, outside of your own lab and a Brookfield ..where can you grab the number?

 

[jstutz]

Originally Posted By: lipadj46
That is the walther formula, cool thanks. That is less accurate than the vogel formula though I'm not sure by how much or at what extremes they start to diverge.


I am not very familiar with the vogel equation but i think you may need three viscosity inputs which makes it unusable for the most part for the avg guys like us being we are only given two variables. I also remember reading about the vogel being more accurate but honestly i cant remember why. I seem to remember it being an issue of the cold temps.

 

[jstutz]

Gary, maybe your on to something here. HTHS is simply the viscosity at 150C right? If thats the case then it would certainly work in the vogel equation. When i get some free time, ill plug in the numbers and compare them to the walther equation. I need to look at the vogel equation ,η = aeb/(T-c), a little more in depth because i believe that variables ab and c are calculated from the kinematic viscosity measurements. Like i said i have not looked into this equation much but i do know that the walther equation is for Newtonian fluids which motor oil is usually not. I have gottn very busy at work lately so i dont have as much time to play with this stuff as much as i used to. Maybe some other math guys could compare the two equations and do a write up for the front BITOG page!

 

[XS650]

Originally Posted By: Gary Allan
flatlander here

Can you even use the HTHS visc as your 3rd POR? Otherwise, outside of your own lab and a Brookfield ..where can you grab the number?


You could but you would be wrong.

HTHS is established with a completely different type of viscometer at a different shear rate. The results are not directly comparible with the viscometer results used at 40C and 100C.

It would be interesting to have the conventional oil viscosity test run at 40C, 100C and 150C and have the high shear test also done at all three temperatures.

 

[jstutz]

Originally Posted By: XS650
Originally Posted By: Gary Allan
flatlander here

Can you even use the HTHS visc as your 3rd POR? Otherwise, outside of your own lab and a Brookfield ..where can you grab the number?


You could but you would be wrong.

HTHS is established with a completely different type of viscometer at a different shear rate. The results are not directly comparible with the viscometer results used at 40C and 100C.

It would be interesting to have the conventional oil viscosity test run at 40C, 100C and 150C and have the high shear test also done at all three temperatures.



Well, here is our answer. If the test is different and do not correlate then they are useless in the equation. Looks like were back with what we have in the widman calc or my spreadsheet.

 

[lipadj46]

Originally Posted By: jstutz
Originally Posted By: XS650
Originally Posted By: Gary Allan
flatlander here

Can you even use the HTHS visc as your 3rd POR? Otherwise, outside of your own lab and a Brookfield ..where can you grab the number?


You could but you would be wrong.

HTHS is established with a completely different type of viscometer at a different shear rate. The results are not directly comparible with the viscometer results used at 40C and 100C.

It would be interesting to have the conventional oil viscosity test run at 40C, 100C and 150C and have the high shear test also done at all three temperatures.



Well, here is our answer. If the test is different and do not correlate then they are useless in the equation. Looks like were back with what we have in the widman calc or my spreadsheet.


I have access to viscometers, I'll just make my own curve

 

[jstutz]

keep me posted

 

[Gary Allan]

Originally Posted By: XS650
Originally Posted By: Gary Allan
flatlander here

Can you even use the HTHS visc as your 3rd POR? Otherwise, outside of your own lab and a Brookfield ..where can you grab the number?


You could but you would be wrong.

HTHS is established with a completely different type of viscometer at a different shear rate. The results are not directly comparible with the viscometer results used at 40C and 100C.

It would be interesting to have the conventional oil viscosity test run at 40C, 100C and 150C and have the high shear test also done at all three temperatures.


I was hoping this would flag you down

Thanks for taking the time. Now start throwing some Alcoa and kidney words around with a commentary from that guy on Jeopardy

(Reynolds .. Stribeck...etc)

 

[CATERHAM]

The problem with the kinematic 40C and 100C vis spec's is that they they don't correlate well with the operational viscosities in an engine.
https://bobistheoilguy.com/forums/posts/2004057/

Instead why not use the HTHS vis at 150C in cP and the MRV vis also in cP typically at -40 degrees. Both viscosity measures involve pressure and shear?

 

[jstutz]

Originally Posted By: CATERHAM
The problem with the kinematic 40C and 100C vis spec's is that they they don't correlate well with the operational viscosities in an engine.
https://bobistheoilguy.com/forums/posts/2004057/

Instead why not use the HTHS vis at 150C in cP and the MRV vis also in cP typically at -40 degrees. Both viscosity measures involve pressure and shear?


Not sure. It seems that the correlation to operational viscosities would be a separate issue. Most just want to see the viscosity over temp curves. It think it would be more helpful to plot the curves simply like widman and then understand what to take from it. Maybe ill try to work those numbers in and see how they compare. I dont have much time to play with stuff like this so it will probably be a while. If we did use HTHS and MRV i wonder how they would correlate. It appears that they would be more accurate at higher temps and lower temps. The margin of error would then probably become the middle ground where most will actually use it. Most lower US guys will never see anything near -40 deg. Personally i would rather see accurate 0F numbers. I havnt read thru the post you posted so ill read thru it later, thanks for linking up to it. I have to get busy so ill check back later and maybe lipad will workout all the numbers and post the charts up .

 

[jstutz]

Originally Posted By: CATERHAM
The problem with the kinematic 40C and 100C vis spec's is that they they don't correlate well with the operational viscosities in an engine.
https://bobistheoilguy.com/forums/posts/2004057/

Instead why not use the HTHS vis at 150C in cP and the MRV vis also in cP typically at -40 degrees. Both viscosity measures involve pressure and shear?


Wow, i just glanced at that post you linked up. Its gonna take me a bit to read thru it. Thanks for linking that. This is the kind of stuff i wish we saw more of here at bitog.

 

[CATERHAM]

HTHS vis correlates well with operating temps well below 150C, in fact I'd say down to 80C or even 70C.
I suspect the very useful MRV at -40 degrees viscosity measure should also correlate well with operational viscosities at warmer although still cold temps. Consiquently estimating an oils viscosity between those two set points covers every oil temp you would really want to know.
One problem with using the 40C and 100C vis set points (aside from the fact that they are kinematic measures) is that they are too close together and the viscosity calulators that use them try to extrapolate to lower temps which doesn't work well.

Interpolating is inherently more accurate to extrapolating so I think using the HTHS and MRV spec's should be something worth looking into.