Hello,
First of all, I'm sorry if my english isn't fully understable, I'll try to be as clear as possible (I'm French)
I'm currently doing some research on a Brookfield VD2T viscometer.
And in order to prepare a future activity, I want to be sure that everything is working well,
My problem is that I have tested a solution of PEG 400 in two different ''condition'', one with a mobile (CPA-40Z) and the other one with the CPA-52Z, they are both completely opposite by their size (CPA-40Z way bigger than CPA-52Z)
But both of them give me ''good results'', I actually don't know how to read those results.
With the CPA-52Z (the small one), 25 rpm, I have a viscosity of 56.93 cP ± 3.72 cP , and even If I increase the speed, I'll get the same viscosity (more or less)
But If I take the CPA-40Z (the bigger one), the viscosity will be different, it's about 12.26 cP ± 0.61 cP , and when I increase the speed, the results are the same
So why do I keed having such difference between my mobile, is this normal?
I plan to see the graph on Excel of Shear rate as a function of shear stress to see if results give me a newtonian fluid graphic, but I'm afraid it won't help me
Hello Rehan,
The best way to know if your viscometer works well and gives consistent results using different cylinders is to test a Newtonian fluid, a mineral oil (without polymer) for example.
Both geometries should give the same viscosity value, by adjusting the rotation speed (thus the shear rate) to get a valid value in both cases.
Also make sure that the sample temperature remains constant and equal during the measurements.
Oh I forgot that I've tried that, but the only newtonian I can think of is water, and only one of my mobile can give me results,
The other one (smallest) gives me under 10% of torque result, which is not recommended to take into consideration
You can use a silicon oil of known viscosity. They are Newtonian fluids as well, and there are various products of different viscosities available. You can chose an oil with a viscosity suitable for both machines. With a measurement of a material of known viscosity you can check also which machine yields the correct value (and correct the other machine). I used a silicon oil of a viscosity of 5000 cSt for such a purpose (but of cause I used a different rheometer).
Also, there are several standard liquids with a standard value of viscosity, the viscometer can be calibrated using these liquids.
Rotational rheometers are not well suited to measure the viscosity of water, because water has such a low viscosity. Thus a fluid with significant higher viscosity needs to be used.
You can use one of these liquids
https://www.selectscience.net/products/viscosity-standards/?prodID=204580
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