Newtonian Pressure Drop vs Non-Newtonian Prssure Drop 2

[Alfarek]

Hi,

I did some experiments on Newtonian and non-Newtonian fluids measuring the pressure drop through a horizontal pipeline. The Newtonian two-phase flow was water+air and the non-Newtonian was (water+xanthan gum)+air.
I prepared 2 samples (2 concentrations) of the xanthan gum solution 1g/1L (995 kg/m3) and 2g/1L (990 kg/m3). I am wondering if it is logical that the Newtonian pressure drop was bigger than the non-Newtonian one?! Also the 2g/1L sample should've been with a higher density comparing to the 1g/1L!

Thanks

 

[BigInch]

It could be logical, but maybe not. It depends on the shear stress related to the velocity of the fluid in each experiment. Were they the same? Were they different? Why? If the effective shear stress could have been more in one experiment than the other, you could get any of a number of results. Two phase flow of liquids and gases is very difficult to correlate in itself without adding what could be extreme nonNewtonian complications.

 

[Alfarek]

Thanks a lot for a quick response.

Yes the velocities were the same for both. The purpose of the work was to compare the pressure drops at the same rates. The xanthan gum solution gets less viscous as the shear stress increases so, when we increase the flow rates, the shear stress increases and it will result in a small pressure drop. While just the opposite happens with the newtonian fluids at the same rates. what do u think?

Thanks

 

[BigInch]

Yes, with non-newtonian flows the increased shear rate (velocity, flow rate) can result in decreased pressure drop. Or holding the same pressure drop on the pipe inlet to outlet can cause a substantial increase in flow rate over time.

The key is the fluid's shear stress to shear rate curve.

 

[Alfarek]

Thanks. That's really helpful.

 

[Latexman]

Have you used Search (between Forum and FAQs) to look for pertinent posts?

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[chicopee]

Perhaps one to two years ago I posted titles and dates of articles written in the Chemical engineering periodical about non Newtonian liquids. I still have the articles and if interested I'll list the dates so that you can procure copies of these articles. Let me know.

 

[Alfarek]

Latexman, I'm still searching for related topics.
chicopee, yes please I'm really interested.

Thanks guys.

 

[Latexman]

Chicopee - are these the references you are referring to? thread378-243822

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[Latexman]

Alfarek - put "non-Newtonian" in the Subject block and search the full site, any date, forums. That will get you started. Then try other pertinent terms, like power law, dilatant, shear rate, etc.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[Latexman]

1 or 2 g/L. Not too concentrated. Have you looked into the friction reducing phenomenon by adding small quantities of polymers to water? Maybe your system is in that range.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[chicopee]

Ron Darby is the main contributor eventhough there are collaborators to the subject of non Newtonian fluids in chemical engineering periodicals listed as follows:
1) take the mystery out of non-newtonian fluids- march 2001
2) pressure drop for non-Newtonian slurries-may 2000
3) predict friction loss in slurry pipes-September 1992
A much older article by Martin H. Wohl:
1) Designing for non Newtonian fluids-January 1968
There are possibly updated articles, however, by that time, much to my regret I stopped subscribing.

 

[Alfarek]

Latexman, I measured the density again using a modern device and I got 1.158(g/cm3) 1g and 1.1349(g/cm3) 2g. The concentration 2g/L is the maximum my flow loop can handle because I couldn't reach to the highest flow rates when the 2g fluid was flowing through the loop.
I found good topics answer some of my questions. Thanks so much.

chicopee, Thanks a lot.

 

[Alfarek]

Is there any way to measure the shear stress in the flow loop by knowing the pump specs?

Thanks