Non Newtonian Pressure Drop Calculation

[RJB32482]

Hello,

I am researching how to calculate pressure drop of a non newtonian (power law) fluid when it is in the turbulent flow regime.

I read the "Facts at Your Fingertips" for Fluid Flow in Chemical Engineering magazine (December 2008) to calculate the friction factor for power law fluids. I have all of the parameters to calculate the friction factor. Now do I just calculate the pressure drop per length of pipe like usual?

h/L=(fV^2/D2g)

If not, what correlation do I use after I find the friction factor for a power law fluid in the turbulent flow range?

The equations for finding the friction factor is based off of Ron Darby's article "Take the Mystery Out of Non-Newtonian Fluids" From Chemical Engineering Magazine March 2001. I have ordered a copy of this article for future use.

Thanks in advance.

 

[BigInch]

Power law or some other nonlinear relationship with velocity calculates the viscosity. Use that viscosity to calculate Reynolds number and then the friction factor. Once you have the friction factor than you can calculate the pressure drop per foot and sum that over the distance where that velocity prevails. If velocity changes, go back and do another power law - viscosity - RE - f calculation again.

I hate Windowz 8!!!!

 

[JJJ2000]

If you are willing to spend the money, it might be a good idea to buy the 2nd edition of Darby's book (1st edition won't work). He walks you through using a "power law model" Reynolds number, which can be used as normal with either the Hooper-2K method or his own 3K method.

I have used the Darby 3K method with the power-law-model Reynolds number with success. I bought the book after seeing it endorsed in this forum in the past. I am confident that there are posts here that can help you.

You can preview the book using Google books (see page 214 of the second edition). Non-newtonian fluids will most likely be a part of my life for years to come, so I didn't mind springing for the book.

Good luck

 

[RJB32482]

Thank you for the replies.

The reason for the calculation is that we are changing our emergency dump piping for one of our polystyrene reactors. The piping is going to be 6" schedule 40.

I know the power law variables and the temperature and material. I was just confused when the Ron Darcy article I read just told you how to calculate the friction factor. I assumed that after that you could calculate flow from pressure drop (I have the pressure in the reactor head space and static head of the polymer melt).

Again thanks for the replies. I appreciate the help in this forum. I have done hundreds of newtonian fluid hydraulic calcs, but none with a power law fluid.

 

[Latexman]

Just be sure the f calculation is for the correct flow regime per the N_RE as calculations are done. You stated it is turbulent. Is it? When everything converges to a final answer, I'd double check it. Also, some f correlations span from laminar to turbulent, and some do not. Be careful.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.