viscosity- how to establish values

[pippo]

people,

 

trying to find viscosity of different liquids, and have not been able to find any practical methods- easy to devise. On this, I have hardly any equipment (centepois meters???) I heard you need graduated cylinders, glass marbles, stopwatch, thermometer, etc, but no real step wise methods. I take it water is perhaps, a standar 1.00 or something of that nature? (like pure H2o is almost 1.0 density @25 deg C)

 

Any help appreciated.

Edited June 7, 2012 by pippo

[doG]

Here in the lab I use a Brookfield dial reading viscometer that I routinely check with a viscosity standard obtained from Brookfield as well. While water is used as a standard for specific gravity it is not a suitable standard for viscosity. Water is particularly sensitive to temperature when compared with other viscosity standards. Silicone fluids provide good temperature stability and are less temperature sensitive than other standards.

 

I also have some graduated cylinders and various viscosity cups but they do not usually offer a suitable level of accuracy when needed. They are a cheap solution but I would not recommend them for fine measurements.

[studiot]

The method you refer to is known as the falling sphere method and is fully described in BS188.

 

However for liquids as thin as water the sphere falls too quickly to time accurately so a falling piston fitting the graduated tube more closely is used as this drops more slowly.

 

 

[mississippichem]

We use Ostwald viscometers in my lab which work well for high viscosity fluids that are close to Newtonian.

 

Basically you immerse a bent capillary tube [viscometer] into a large water bath (to control temperature), pull up some liquid with a pippette bulb and measure how long it takes to fall a certain distance.

 

Downsides:

 

-each viscometer has it's own measurement constant. If you don't know it then they are useless.

 

-high precision is not really achievable because of human error in the timing.

 

-no good for low viscosity fluids (I measure very viscous monomer and prepolymer mixtures)

 

If your fluid deviates from "Newtonion-ness" too much you'll probably need a rheometer.

Edited June 8, 2012 by mississippichem

[pippo]

tHANKS, PEOPLE. iNTERESTING FOR SURE. i CAN SAY THE FLOW OF THE FLUIDS I AM WORKING WITH ARE , WELL, VERY THICK. lIKE HONEY, BASICALLY. oops- sorry about the caps........

 

Looks like there is no short cut- cheap way. But, I can still achieve what I want- I'll just sent various samples to customer, as he has to decide which viscosity he needs anyway, so no problem- I'll just have to remember, with thehelp of good notes, how I made it (example, g/L, etc.

 

Thanks

[studiot]

If the fluid is as viscous as you say, you can drop marbles or ball bearing into a graduated tube (plastic is safer) about 300 mm tall and time the fall between marks with a stopwatch or good wristwatch.

 

 

You should be able to calibrate the tube (or its twin) with standard two stroke oil its viscoscity is tightly controlled.

 

That shouldn't cost too much.

Edited June 8, 2012 by studiot

[pippo]

If the fluid is as viscous as you say, you can drop marbles or ball bearing into a graduated tube (plastic is safer) about 300 mm tall and time the fall between marks with a stopwatch or good wristwatch.

 

 

You should be able to calibrate the tube (or its twin) with standard two stroke oil its viscoscity is tightly controlled.

 

That shouldn't cost too much.

 

Good tip, studio. never thought of that. Auto parts store here I come......