viscosity

[picasa]

SSU is a unit of viscosity. I believe it is unit for kinematic viscosity (centistokes) and not dynamic viscosity (centiPoise). The relationship between centistokes and SSU is something like logarithmic or exponential - I dont know, but that is what I am trying to find! Where can I find an equation relating the two? Does this equation change depending on the fluid and fluid properties (pressure, temperature etc.)

 

[Ashereng]

Common used units for viscosity are

CentiPoises (cp) = CentiStokes (cSt) x Density
SSU(Note1) = Centistokes (cSt) * 4.55
Degree Engler(Note1) * 7.45 = Centistokes (cSt)
Seconds Redwood(Note1) - 4.05 = Centistokes (cSt)

Note1 - centistokes greater than 50

There are two related measures of fluid viscosity - known as dynamic (or absolute) and kinematic viscosity.


I found this via google at:

http://www.engineeringtoolbox.com/dynamic-absolute-kinematic-viscosity-d_412.html

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[21121956]

From the brochure DG-400 by EXXON we can read:
"Many petroleum products are graded according to the ISO Viscosity Classification System, approved by the International Standards Organization (ISO). Each ISO viscosity grade number corresponds to the mid-point of a viscosity range expressed in centistokes (cSt) @ 40ºC. For example, a lubricant with an ISO grade of 32 has a viscosity within the range of 28.8-35.2, the mid-point of which is 32.

Rule-of-Thumb: the comparable ISO grade of a given product whose viscosity in SUS at 100ºF is known can be determined by using the following conversion formula:
SUS @100ºF + 5 = cSt @40ºC. "

 

[25362]

Centistokes (Z), are estimated from SSU (S) as follows:

for S < 100: Z = 0.226[&times;]S - 195[&divide;]S​

for S > 100: Z = 0.220[&times;]S - 135[&divide;]S​

A similar thread in the past dealt with this subject, but I'm too lazy to look for it.

 

[picasa]

25362:

For S values less than around 30 SSU, the value of Z calculated per your formula is -ve! Is that correct?

 

[jmw]

It was my understanding (I could be wrong) that Saybolt was one of the "obsolete" units though it wouldn't be surprising for it still to be in use along with Engler, Redwood and a few others.
Visit

http://www.viscosity.com

where Norcross maintains a nice set of conversions.
Go here for a converter:

http://www.softslide.com/volumes/v3/t3/p1/

More tables here:

http://www.coleparmer.com/techinfo/...cosity.htm&Title=Viscosity+Conversion+Factors

not forgeting:

http://www.engineeringtoolbox.com/dynamic-absolute-kinematic-viscosity-d_412.html

JMW

http://www.ViscoAnalyser.com

 

[unclesyd]

There is an excellent free downloadable conversion program, Unconeer, at this website.

The author is a regular participant of Eng-Tips.

http://www.katmarsoftware.com

 

[picasa]

There has to be some published peer-reviewed sources which describe this conversion. I am looking for those sources. Do not mean to imply that these website are no good, but they can change in the future!

 

[25362]

To picasa, according to the approximate formulas I quoted from old argentine YPF tables, definitely yes. Tabulated values I have for 210^oF are:

Z S Z by formula % deviation

2.0 32.8 1.47 -26.5
2.5 34.6 2.18 -12.8
3.0 36.3 2.83 - 2.3
3.5 37.9 3.42 - 2.3
4.0 39.4 3.89 - 2.8
4.5 41.0 4.5 zero
5.0 42.6 5.05 1.0
10 59.2 10.08 0.8
20 98.2 20.2 1.0
50 233.0 51.8 3.6
70 325.7 73.0 4.3
90 418.7 94.1 4.6
100 465.2 104.7 4.7

Which shows the formulas are a gross approximation, and a graph would better serve for extrapolation at the lower end.
Also, please note that temperatures slightly affect the conversion.

Beside all that, the conversion factor above 70 cS is said to be constant, 4.62 for 100^oF, and 4.652 for 210^oF.

 

[jmw]

Actually, there is an ASTM standard somewhere that will be what you want: WK5950 Standard Practice for Conversion of Kinematic Viscosity to Saybolt Universal Viscosity or to Saybolt Furol Viscosity


JMW

http://www.ViscoAnalyser.com

 

[jmw]

ps to make that real easy:

http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/WORKITEMS/WK5950.htm?L+mystore+lpmb9550

JMW

http://www.ViscoAnalyser.com