Viscosity / Pressure Estimation for Epoxy Compound
Viscosity / Pressure Estimation for Epoxy Compound
(OP)
I need to estimate the pressure needed to force a high viscocity fluid from a container (55 gallon drum/barrel) at a given flow rate (<=1gpm). I'm thinking I'll have a 2" hole for out flow in a follower plate, which is where the pressure is applied. Unfortunately, I don't know the fluid viscocity, and I can only get a quantity of about 1 quart to experiment with before the prototype stage, when I'll be able to try it out with either 1 or 5 gallon containers. It's way too thick for a Zahn cup-type measurement, the material being similar to Bondo fairing compound in autobody applications (like thick mud). Any ideas of how I can get a rough idea of the pressure needed?? With those numbers I could get started on the rough design, and verify flow rates in the prototype stage.





RE: Viscosity / Pressure Estimation for Epoxy Compound
JMW
www.viscoanalyser.com
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RE: Viscosity / Pressure Estimation for Epoxy Compound
RE: Viscosity / Pressure Estimation for Epoxy Compound
Viscosity is the ratio of sheer stress to sheer strain. For simple fluids, Newtonian fluids, this ratio is always constant. For other fluids it isn't.
Let me explain, for simple fluids like water, we can assume a Newtonian behaviour; the viscosity is a constant even as the shear rate changes.
Something like starch, the viscosity increases when you increase the shear rate (Dilatant) so you tend not to put too much energy in; the more energy you put in the thicker it gets.
On the other hand, something like toothpaste behaves like a solid, with no energy input, but as you put energy in the viscosity reduces significantly.
The more complex the molecules, the more complex the behaviour. With fluids like thick oils, easy, you can heat them and the viscosity drops and the behaviour changes to Newtoniain. Some fluids you can't heat, you just have to be careful how you impart energy.
Thing is, you have to know what the shear dependent behaviour is and know how much sheer you will put into the fluid to know the behaviour.
This means that with a fluid you describe as "like bondo" you can't use a cup measure anyway, it isn't suitable for non-Newtonian fluids. Something like a cone and plate meter will let you know what type of fluid you are dealing with and how viscosity varies with shear rate.
Your forumala depend on you knowing the viscosity at your operating conditions of temperature and shear rate.
I'd beg or borow that meter or get someone to run some tests on a sample for you.
JMW
www.viscoanalyser.com
Eng-Tips: Pro bono publico, by engineers, for engineers.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Viscosity / Pressure Estimation for Epoxy Compound
I'm still looking for that viscometer. I assume one will allow me to measure viscosity at various shear rates, so I can get a picture of the rate-dependency of the fluid. How would I relate a desired flow rate from a vessel into a tube/pipe back to a known shear rate/viscosity?
RE: Viscosity / Pressure Estimation for Epoxy Compound
ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee
RE: Viscosity / Pressure Estimation for Epoxy Compound
In addition the the rheology of materials. There is more to it than just shear rate. Thixotropic and rheopectic fluids exhibit shear thinning or thickening with time, at a constant shear rate. Meaning with a constant energy addition, it is the length of time that the material is sheared, and not the level of agitation.
I've dispensed epoxy, and developed a dispensing machine for epoxy. I remember pulling pretty hard on the piston to get the stuff to move, and since it moved a very short distance, I didn't see much change in pressure requirements or viscosity.
You might find a good deal here.
http://www.labequip.com/itemcatalog/category/Physical/Brookfield-Viscometers.html
RE: Viscosity / Pressure Estimation for Epoxy Compound
If someone out there has some viscosity data on AwlFair, it would be greatly appreciated. Maybe I should post in the chem section?
RE: Viscosity / Pressure Estimation for Epoxy Compound
RE: Viscosity / Pressure Estimation for Epoxy Compound
I'll probably be posting on the topic of dispoable static mixers for high viscosity fluids (same project) in the near future, but I need to do some research first since I've already located a few threads here about it. Thanks again!