×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Plotting Viscosity Data and making the ASTM D341 Graph (Logarithms)

Plotting Viscosity Data and making the ASTM D341 Graph (Logarithms)

Plotting Viscosity Data and making the ASTM D341 Graph (Logarithms)

(OP)
Hello all,
There's been a few discussions on the Walther equation for plotting the viscosity/temperature relationship of lubricants. I'm trying to basically make my own plot...but I am having trouble understanding the vertical scale to use to get the linear relationship. I think I've puzzled out how to make a log scale. But, the log log needed for this equation isn't working out.
The ASTM d341 chart uses this scale. And while I could download the graph...that's not going to tell me how the vertical scale was created. I sure appreciate the help.
(the "why" is a much longer story)
Thanks,
Andy

RE: Plotting Viscosity Data and making the ASTM D341 Graph (Logarithms)

show us the equation for which you want a log-log graph paper.

RE: Plotting Viscosity Data and making the ASTM D341 Graph (Logarithms)

actually if you look more carefully you will notice that the horizontal scale is a log scale (in K, but usually values are shown in degrees C) and the vertical scale is a loglog scale. only then you can get a straight line based on the Walther equation.

with standard spreadsheet software you will not be able to make a chart like that, because you will not be able to get the vertical scaling needed.

RE: Plotting Viscosity Data and making the ASTM D341 Graph (Logarithms)

(OP)
Walther formula[edit]
The Walther formula[1] is typically written in the form

log_{10}[\log_{10}(\nu+\lambda)] = A - B\,\log_{10}(T)

where λ is a shift constant, and A, B are empirical parameters.


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


RE: Plotting Viscosity Data and making the ASTM D341 Graph (Logarithms)

Walther's formula:
(ν+a) = bd1/Tc

where:
a, b, c, d are constants
ν is the kinematic viscosity (m2/s)
T is the absolute temperature (K)

It has been found that if ν is in cS, then a ≅ 0.6. By taking d=10 and log twice one gets:
log10log10cS+0.6) = log10(log10b+1/Tc)

Although an incorrect derivation of the above equation, the ASTM viscosity-temperature chart ewhere the ordinate is log10log10cS +0.6) and the abscissa is log10T, is quite successful when used on oils (mineral and synthetic) under "normal" conditions.

RE: Plotting Viscosity Data and making the ASTM D341 Graph (Logarithms)

I'm using the post above to refresh my memory.
You could build a table:
T, v, X, Y, X1, Y1.
T is the independent variable Ttemperature (in the correct units)
v = b*10^*(1/T) - 0.6
Y = log(log(v + 0.6)
X is log(logb + 1/T) (plug in whatever b is… I'm working from what is posted above).
Y1 = (log(v + 0.6)
X1 is (logb + 1/T) (plug in whatever b is… I'm working from what is posted above).

Then if you a simple excel linear plot Y vs X or log log excel plot based on Y1 vs X1 I think you would have a straight line on your graph (slope 1 on the linear plot). The only problem is the axes are not v and T. You could take out all auto-generated gridlines and tickmarks and build your own vertical gridlines using extra series with constant values of T and your own horizontal gridlines with constant values of v.

Labeling those gridlines would be the challenge. Two approaches:
1 - You could add labels manually (for example in powerpoint) and get a nice pretty chart.
2 - If you wanted excel to do it you might keep it a small number of gridlines to keep it manageable and label the gridlines using the normal series label feature. Then to read the scale you wouldn't look at each gridline and then at the legend to figure out the values associated with the gridlines. Easier for you to build but not as pretty when you're done.

=====================================
(2B)+(2B)' ?

RE: Plotting Viscosity Data and making the ASTM D341 Graph (Logarithms)

Quote:

(plug in whatever b is… I'm working from what is posted above).
hmmm, maybe not. I'm remembering now given two sets of (T,v) you can solve the constants and plot a curve in the T,v plane (which is not a straight line) and read off any value you want. With computers that seems like the easy way. You don't need the ASTM graph paper anymore unless you don't have access to computer.

=====================================
(2B)+(2B)' ?

RE: Plotting Viscosity Data and making the ASTM D341 Graph (Logarithms)

(OP)
Thanks for sharing your spreadsheet. I am beginning to think the brute force approach is going to be needed...where I plot all of this out in AutoCAD. Wish me luck!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources