viscosity calculation 1

[saliba11]

using ASTM D 341, If I had two values of viscosities at two different temperatures I could fit those values in the above equation and found the fuel constants A and B and then interpolate to find the value of viscosity at a different temperature.

Presently, I know the viscosity of a Heavy Fuel Oil which is 1200 cSt at 50 deg C. I wanted to know how to calculate the viscosity at 60 deg C.

could anyone provide me a method about this subject

 

[GregLamberson]

saliba11

This link might help:

http://en.wikipedia.org/wiki/Temperature_dependence_of_liquid_viscosity

Generally the viscosity is measured at a cou0ple of (2 or more) temps and interpolating for any other temps needed. When you can't measure for some reason, we ususally use a temp/viscosity chart from ASTM.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[25362]

From old graphs for these type of residual oils I'd say that 550 cSt at 60^oC [±] 50 cSt would be in the ballpark. Of course, it all depends on the composition, e.g., aromaticiy (low VI) and paraffinicity (high VI) of the fuel.

Best would be to have a viscosity at, say, 100^oC and interpolate using a standard viscosity/temperature chart.

 

[BigInch]

Could try this. It ain't easy though. Other unknowns to contend with.

http://www.mcs.utulsa.edu/~class_di...s_law/node15.html#SECTION00152000000000000000

http://virtualpipeline.spaces.msn.com

 

[25362]

BigInch, I assume that link refers to "simple" (single) liquid compounds, but is it applicable to mixtures of unknown composition such as a heavy (almost bitumenic) fuel ?

 

[BigInch]

That I don't know. As always, crudes can be tricky. Heavier crudes even more so, since there may be some nonNewtonian complications.

In any case the crudes I have known still roughly followed a straight line plot of Log viscosity vs absolute temp.

My WAG would be a little higher than yours, maybe 650 to 750 at 60ºC, hitting 550 at around 70ºC, but my guess may be weighted towards the heavier than average heavies.

http://virtualpipeline.spaces.msn.com

 

[25362]

IMHO such a viscosity would indicate a higher paraffinicity than normally expected in this kind of fuels.

There are other formulas mostly empirical for oils. One used for narrow temperature ranges is that attributed to Reynolds:

[η] = be^-aT​

where [η] is the dynamic viscosity, a,b are empirical constants, e the base of the natural logarithms, and T is the absolute temperature.

Then there is the one by Slotte:

[η] = a/(b+T)^c​

with the same meanings plus c as an additional empirical constant. This formula is reasonable, and used in mumerical analysis.

There are also the Walther formula for kinematic viscosities, used as basis of the ASTM visc-temp chart, and that by Vogel considered the most accurate and useful in engineering calcs.:

[η] = ae^b/(T-c)​

The above info. was taken from Engineering Tribology by Stachowiak and Batchelor of the Tribology Series #24, Elsevier.

 

[jmw]

I'd guess it at around 580cst, (+/-)1.0%.

If you download the spreadsheet from

http://www.viscoanalyser.com/page8.html

you will see it is populated with a range of fuel properties (from CIMAC) and shows the A and B values. It also shows the viscosities at a range of other temperatures.

By entering the 1200cst at 50 as one set of data I increment the viscosity at 100degC till I get a reasonable set of A and B values.
In this case 70cst seems to give the most reasonable incremental change in A and B. 71cst is too much (582cst) and 69cst seems too low (577cst).
Of course, this is not accurate (nor was my approach as rigorous as it would normally be because I feel lazy today): it assumes that fuels show proportional properties to each other and that the reference curves are representative.
You couldn't do this with lubricants but these are reasonable assumptions with fuels and where the target temperature is reasonable compared to the datum temperature.

Going from 50C to 60C is probably OK, going any further afield or trying to go to deep into lower temperatures would not be so clever because the curves diverge.

The problem of finding the viscosity at one temperature when you only know the viscosity at one other temperature is a perennial one. The most serious approach would appear to be the Shell V50 equation but I am not sure that it really works or that is always properly used.
However, most fuel blend calculators assume that this is exactly the case in the industry; that most people will only have the viscosity at one temperature. (it helps that they only adjust the distillate viscosity which is a flat curve) but they also go so far as to calculate the injection temperature (temperature at which the viscosity is the target value e.g. 12cst) based on a single temperature point. But this doesn't have to be too accurate and any way, this is calculating back into convergence.

None the less, with care effective and accurate (1.0% of reading)process viscosity measurement solutions assume the proportionality rule for fuels and that enables a single viscometer to measure the viscosity at the process temperature and then calculate the viscosity at the reference temperature.... using a set of reference curves to work out the proportions.
Actually, since most operators don't bother to change the curves from the default set (the set in the spreadsheet) the results are usually pretty good.

Errors using this approach are less where the target temperature is pretty close to the temperature at which you have the actual viscosity.
In practical terms this means process temperature usually from 40-60C and reference temp 50C.

JMW

http://www.ViscoAnalyser.com

 

[BigInch]

25362,

Could be, as my internal reference frame is probably shifted to the right.

The URL I gave seems to be of the same form as the Vogel equation.

http://virtualpipeline.spaces.msn.com

 

[jmw]

I think the Viscosity Gravity constant (ASTM D2501-91(2005)), a function of the density and the kinematic viscosity at two temperatures, is an indicator of paraffin or kerosene composition, but I could be wrong.

The trouble with any of these equations is that they have more than one constant.
With the expression for density we can simplify and use the same constants for all gasolines, another set for all kerosenes, another set for crudes and another set for fuel oils.
This means that although the calculation is iterative, we can at least find the density at one temperature from a single measurement of the density at another temperature. Of course, we can also solve for the precise values for K0 and K1 but the default values give acceptable accuracy.

I think the Shell V50 was an attempt to reproduce this approach with viscosity.

But, with viscosity, the "constants" change significantly even for small quality changes in the product.
This means you always need to solve for the values of the constants each time you make a measurement.
In the ASTM D341 equation you have two constants and so you need two solutions to get a good answer. All else is approximation, sometimes good and sometimes bad, depending on how you do it and under what conditions.

For fuel oils we can exploit the "proportionality" to derive viscosity at one temperature from the viscosity at a single temperature, using reference curves, with good effect under limited conditions. Outside those conditions we are back to using the viscosity at two different temperatures to find the true A and B values and then solving for the viscosity at the temperature of interest.

In the expression quoted by Biginch, we still have to find the values for the constants and that means we need more than a viscosity at a single temperature, or so I believe.

PS 25362,
by aromaticity are you meaning the same thing that is meant by the CCAI (Calculated Carbon Aromaticity Index) and its equivalent CII (Calculated Ignition Index) which are also on the spreadsheet and calculated according to BS MA 100 from the viscosity and density? or the ASTM D2501 expression above?

JMW

http://www.ViscoAnalyser.com

 

[25362]

To jmw, I used the word more in the sense of the VGC. My estimate was based on certain old data on a chart I found on heavy fuels. I assumed it could be an M9 class on the BS MA100:1982.

Estimations made from this old chart can not be regarded as precise because the V/T relationship depends on the crude oil source, and the refining processes used. Therefore, any estimate may be wide off, especially when dealing with high-viscosity fuels.

Since a limited number of heavy residuals may have a non-Newtonian behaviour at 50^oC a better temperature level for reference would be at least 80^oC.

Saliba11 would have to find another viscosity at a higher temperature for satisfactory burning and transfer of this fuel.

 

[Malimedo]

I'd like to help, but I'm not into chemical engineering, only in PVT and Petroleum Eng.
However, maybe It will be interesting to try Vasquez Beggs and similar correlations:

http://fekete.com/software/welltest/media/webhelp/c-te-fluidprops.htm

http://www.ipt.ntnu.no/~asheim/ovinger/Fluid properties.doc

As I understand, this should be more trivial situation, as you don't have dissolved gas, so your playing with abovementioned correlations should stop with calculating viscosity of dead oil (miOD, ie. viscosity at atmospheric pressure and some temperature).
As you can see, sometimes, only oil gravity and temperature are needed for calculation.

 

[BigInch]

Those are some handy documents. Thanks for pointing them out Malimedo.

http://virtualpipeline.spaces.msn.com