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Topic: Is there a way to calculate flow out of a rotor stator mixer?

posed by  Last edited: 15 May 2013 At 11:23am
I have a question about batch-style rotor stator mixers. Is there a way to calculate flow out of a rotor stator mixer? Do they have power numbers and pumping numbers like other blades? I can calculate tip speed easily and tip speed seems to correspond to shear rate. But when it comes to calculating tank turnovers, I have no idea how much my rotor stator is pumping. Is this information I can get from the manufacturer?
  • Avatar Dave Dickey Forum Moderator 288 Posts

    Re: Is there a way to calculate flow out of a rotor stator mixer?

    Values for pumping numbers, power numbers, and the effects of shear rate all come from experimental measurements.  Most mixing correlations come from empirical measurements.  Computational methods have limited capabilities for complicated impeller geometries, such as rotor stator mixers.

    To calculate flow out of a rotor stator mixer, you need an experimentally measured pumping number.  Rotor stator mixers potentially have power numbers and pumping numbers, but they are not published in the open literature.  Tip speed will represent a shear rate for the rotor stator, but that will not directly predict a drop size or particle size.  Again experimental measurements are needed.  Rotor stator mixes have different geometries from different manufacturers.  Perhaps, the manufacturers can give you some additional information.

    Most applications for rotor stator mixers are sufficiently unique that some form of testing is required.  Those test results will be difficult to generalized to pumping numbers and power numbers.  Even a pumping number and turnover calculation are not likely to predict the extent of mixing because of different flow patterns for different rotor stator mixers.

    The answers by this expert are based on the best available interpretation of the information provided. The consequences of the application of this information are the responsibility of the user. If clarification is needed, please submit a further question.

  • Avatar Elliott Meckley Community Member 1 Post

    Re: Is there a way to calculate flow out of a rotor stator mixer?

    So it sounds like rotor stator mixers differ so much in design from regular mixers that they don't correlate the same? This makes sense because depending on if you're looking at a Ross or Silverson they have different blade geometries, stator heads, etc. We have a process that we are working on scaling up. We successfully mixed ~500 mL of solution under a rotor stator at ~4500 rpm and we are trying to scale up to a ~5 gallon batch. I am making sure that we keep the same tip speed as the smaller scale to keep the shear rate similar. I am having trouble calculating mixing time. For 500 mL we mixed for 15 minutes which without a pumping number I can't calculate how many times the batch was turned over. So I have no way of knowing how long to mix the large ~5 gallon batch. P.S. I work in a mixing heavy environment and I just found this forum. Thank you for all your replies you are incredibly helpful.