12 replies to this topic

[alameehs]

good day

 

I need you assistance to calculate oil viscosity at 100 C. i have the viscosity of it at 90 C which is 13.5 cST. the specific gravity of mixture is 1.003. Is there a correlation to calculate viscosity if temperature available

 

thanks

[PingPong]

Relation between viscosity and temperature depends on the nature of the oil.

 

An oil with a s.g. of 1.003 and a viscosity of only 13.5 cSt at 90 ^oC does not look like a common petroleum oil.

 

What kind of oil is this?

[alameehs]

Hi Sir

 

Its pyrolysis fuel oil. its coming from hydrocarbon paraffin cracking.

 

thanks  

[alameehs]

gentlemen

 

I found two viscosity points at two deferant temperature which is as follows

1.13.9 cP at temperature of 90 C

2. 8.83 cP at temperature of 138 C

what I need the viscosity at 100 C

[PingPong]

For hydrocarbons you can use the ASTM D341 equations or graphs.

 

JMW has made a spreadsheet available for the calculation:

https://www.cheresou...ity-calculator/

 

Note however that the ASTM D341 method works with cSt, not cP.

 

So if you have viscosities in cP as in post #4 then you first convert them to cSt using the SG at the indicated temperatures..

The calculated viscosity at 100 ^oC is then also in cSt so if you need it to be in cP you have to convert it to cP using the SG at 100 ^oC.

[gegio1960]

alhamees,

you should have (or estimate) density (or cst) at the 2nd temperture....then you can draw a line 

you can easily find the relevant equations/excel files

good luck

Attached Files

•  VicosityChart.pdf   801.02KB   30 downloads

[PingPong]

The graph that gegio posted is from ASTM D341.

 

Using the graph is easy: just plot the available viscosity points (in cSt) and draw a straight line through them.

The formulas, like in JMW's spreadsheet are more accurate.

 

In this particular case one could also look at the numbers and say:

hmmm, the viscosity at 100 ^oC must about 13

[sgkim]

Alhamees, 

 

Not knowing densities at different temperature, the dynamic viscosity can be estimated from the Arrhenius-type model equation: (http://www.academicj...312_Stanciu.pdf)

 

ln μ1 = A + B ln T1...(1)

ln μ2 = A + B ln T2...(2)

----------------------------------

ln(μ1/μ2) = B ln(T1/T2) ==>  B = ln (μ1/μ2) / ln(T1/T2)  ....(3)

A =ln μ1 - B ln T1 = ln μ1 - {ln (μ1/μ2) / ln(T1/T2)} ln T1  or   A = ln μ2 - B ln T2 = ln μ2 - {ln (μ1/μ2) / ln(T1/T2)} ln T2 ....(4)

 

Therefore,

ln μ3 = A + B ln T3...(5)

= ln μ1 - {ln (μ1/μ2) / ln(T1/T2)} ln T1 + {ln (μ1/μ2) / ln(T1/T2)} ln T3   or  = ln μ2 - {ln (μ1/μ2) / ln(T1/T2)} ln T2 + {ln (μ1/μ2) / ln(T1/T2)} ln T3

=ln μ1 -{ln (μ1/μ2) / ln(T1/T2)} ln (T1/T3)   or  = ln μ2 -{ln (μ1/μ2) / ln(T1/T2)} ln (T2/T3) ......(5)

 

Then 

μ3  = exp { ln μ1 -{ln (μ1/μ2) / ln(T1/T2)} ln (T1/T3) }   or  = exp { ln μ2 -{ln (μ1/μ2) / ln(T1/T2)} ln (T2/T3) }

=μ1 * (T3/T1)^{ ln (μ1/μ2) / ln(T1/T2)}  or  = μ2 * (T3/T2)^{ ln (μ1/μ2) / ln(T1/T2)} .................(6)

 

Use dynamic viscosities[Pa*s] for μ1,  μ2,  μ3 and absolute temperatures[K] for T1, T2, and T3.  If you have a log-log sheet, simply locate the previous known data (ln T1, ln μ1) and (ln T2, ln μ2) and connect the two points then find (ln T3, ln μ3) on the straight line (ln μ = A + B ln T).   

 

~ Stefano Kim

Edited by sgkim, 23 March 2017 - 01:52 AM.

[Profe]

Hi Alameehs

 

For your question, use the API Procedure 11A4.1 to calculate the viscosity knowing only one viscosity.

The procedure uses the viscosity in cSt at 100°F.

 

For your case, I use some tricks for get the viscosity at 100°F, and then with this value I calculate the viscosity at temperature needed of 212 °F (100°C)

 

Attached the excel file for that. Review the worksheet and try to repeat the procedure that I follow and the PDF file for  API procedure 11A4.1

Source: API - Petroleum Refining Technical Data Book pag 11-33 to 11-34.

 

Good luck

 

Fausto.

Attached Files

•  Viscosity procedure API 11A4.1.pdf   27.07KB   30 downloads
•  viscosity.xlsx   330.37KB   20 downloads

Edited by Profe, 23 March 2017 - 07:56 AM.

[alameehs]

Thank you very much all of for your help and valuable information that you provide me

[Napo]

Alameehs,

 

I attached related information, from the book Heat Transfer Design Methods by John McKetta.

 

Napo.

Attached Files

•  Oil Viscosity.pdf   4.21MB   28 downloads

[breizh]

Hi ,

The dynamic viscosity ( Po or CPO) should follow this type of model :  ln (mu) = A+B/T  with mu the dynamic viscosity and T temp in Kelvins .

 

The coefficients A.B should be identified if you have data to support at 2 different temperature.

 

In the case you only have the cinematic viscosity you need to get access to the density at the same temperature :

nu (St or Cst) = mu /density .

 

Hope this helps,

Breizh

Edited by breizh, 25 March 2017 - 02:36 AM.

[alameehs]

Thank you very much all of you for your assistance