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Topic: How can I calculate my power number and power required for two different impellers?

anonymous
How can I calculate my power number and power required for two different impellers? I have a solid suspension mixing tank with two different types of impellers but same size as below. Vessel: diameter = 510 mm, height = 710 mm, dished bottom Impeller: one 3PBT45 at bottom and 3-blade paddle at top both diameter = 165 mm, different height = 360 mm Shaft diameter = 35 mm Rotational speed around 1,400 rpm liquid density = 1000 kg/m3 solid density = 8000 kg/ m3 mixing ratio is 2:1 viscosity = 1 mPas
  • Avatar Dave Dickey Forum Moderator 283 Posts

    Re: How can I calculate my power number and power required for two different impellers?

    The power number for the 3PBT45 impeller is 1.19.
    The power number for the 3-blade paddle impeller is 3.28.
    Both 165 mm diameter impellers are assumed to have blade widths of 33 mm.
    A 2:1 mix of 1000 kg/m3 liquid and 8000 kg/m3 solids is a 3.33 kg/ m3 slurry.
    The power required for the mixer is 30 KW total with both impellers.
    The total power for both impellers is the sum of the two impellers separately.
    The shaft diameter needs to be 50 mm, not 35 mm

    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 Roderic Merlini Community Member 1 Post

    Re: How can I calculate my power number and power required for two different impellers?

    Hi, After reading the answer, I understand that in case of multiple impeller stages (mounted on a same shaft), the total power is the sum of the partial power independent of what kind of impeller are mounted on? the space between the two or three impellers are not important too? is that correct ? Thanks for your expertise
  • Avatar Dave Dickey Forum Moderator 283 Posts

    Re: How can I calculate my power number and power required for two different impellers?

    The power required by multiple impellers on the same shaft is usually the sum of the separate impellers.  The power for each impeller should be calculated separately and will depend on the impeller type and even involve impellers of different diameters.  In most cases, the total power is just the sum of the individual impeller powers, unless that impellers are close together.  If the impellers are less than a half an impeller diameter apart, the total power may be slightly less than the sum of the adjacent impellers.  The interaction between impellers is not a common or major problem.