Viscosity / Pressure Estimation for Epoxy Compound 2

[YoungTurk]

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.

 

[jmw]

One thing to try is to find someone with a cone and plate viscometer you can borrow; they use them for bitumens/asphalts and they use about a teaspoon full of sample. As a rotational viscometer you should be able to assess the shear dependent characteristics which may give you some insights.


JMW

http://www.viscoanalyser.com

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[YoungTurk]

I think that would probably work well, if only I could get my hands on one! I'll definitely ask around. I work at a wood research lab, maybe the adhesives department has one. Trick is getting the OK to use it for a home project. Budget is low, I'm trying to get an idea off the ground. Maybe someone could post a link or give ideas on how to construct my own viscometer? Also, would measurements taken in this manner be directly applicable as viscosity in formulas from my basic fluids text for flow?

 

[jmw]

Well, not necessarily. The basic definition of viscosity is very simple and tells you nothing of the rheology.

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

http://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.

 

[YoungTurk]

Thanks for the addtional info. I had a feeling that the shear/flow problem wasn't quite as straightforward as was presented in basic fluid engineering texts.

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?

 

[aspearin1]

You should be able to contact the supplier or manufacturer for this information. They would likely use a target viscosity as a release criteria for their product. A good supplier would provide this information in product literature. If you show promise as a valuable customer, they may even be able to put you in contact with some of their packaging/dispensing people for advice on a system.

ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee

 

[profengmen]

I agree with aspearin, contact the supplier first. Then, if they don't know, you will have to measure it yourself. You can probably rent a Brookfield, I know we rented one before we bought one.
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

 

[YoungTurk]

Yes, I have tried contacting the supplier. Problem is, the original manufacturer, US Paint, has been bought out by Akzo Nobel. The compound I'm working with is called AwlFair, and I can't get an iota of information from anyone related to manufacturing the stuff. Its a proprietary product and has a real monopoly within the industry, amounting to hundreds of thousands of dollars in sales at every shipyard that uses the stuff, which is almost every yacht yard.

If someone out there has some viscosity data on AwlFair, it would be greatly appreciated. Maybe I should post in the chem section?

 

[profengmen]

Ask them for a MSDS sheet, they have to give you that. The viscosity might me on there?

 

[YoungTurk]

Thanks to all for the help! Although the MSDS were a wash becasue they list viscosity as -N/A, I have located a Brookfield viscometer I can use! Thanks to Profengmen for turning me on to the Brookfield name brand, it helps to know what you're asking for at a big lab.

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!