Calculating Viscosity from power draw on a motor??

[brudje]

I am trying to equate power draw on a mixing motor to vicosity of solution?? Ihave been ready up on it, but am having a hard time finding a practical set of equations to do so....

As usual thanks in advanc efor the help...

 

[DesignerMike]

I have done some work with sizing mixers, and the formula has quite a few variables.

You may be able to come up with a number, but I doubt it would be very accurate. Type of mixer, vessel shape, impeller speed will all have an effect.

Probably the most accurate way would be to test with two or three products of a know viscosity and interpolate a aproximation from there.

It will also depend on whether the product is Newtonian, Thixotropic, or Dilatent (if they get thinner, thicker or stay the same due to the mixing affect)

If you are using the same product, and just working on something as simple as adding water to a mix until it reaches a set-point you may have some success.

 

[Latexman]

I was successful at using current draw to predict when molecular weight of a polymer solution was in spec. It was always on the same physical reactor with the same anchor agitator and same motor (keep everything constant!). At the prescribed current draw the polymer was "cut" with solvent.

I never tried to back out viscosity. Too complex. I'd think it'd be better to correlate the power draw with lab data and see how good the correlation is.

Good luck,
Latexman

 

[JStephen]

The power required for mixing wouldn't drop to zero at zero viscosity. IE, with low viscosities, the power would be more or less independent of viscosity. Ok if you're trying to size the motor, but makes it hard to deduce viscosity in that case.

 

[brudje]

DesignerMike, I was thinking the same thing, that the use of known viscosity fluids seems to be the easiest way to go ,and interpolate from there...

I am working a researcher who is formulating a collogen based gel and would like to get a speed/temp/time profile for each given formulation. The motor/vessel are the only constants right now. That is why I was thinking about trying to calculate something based on the fact that we have alot of unknowns. If I can get the temperature range set, then whole thing become a heck of alot easier

Thanks for the responses...Don't you just love research efforts!!! Great challenges....