Power Number (Np) examples for turbines

For improved fermentation the following is good to know

Power Number is a dimensionless parameter used for estimating the power consumed by the agitating turbine. The lower the Power Number the better ability to disperse gas into the media without flooding!

Rushton turbine model RT6-90 is a pure radial flow turbine has an un-gassed Power Number of 4.5 – 6.5 being the highest PN of any common turbine. By far not the best design and based on simple Stainless Steel manufacturing methods 50 years ago.

Jacob’s turbine is an angled flat blade mixed radial and one direction axial flow turbine with blades mounted on a core inside a cage. The model JT8-75 has an un-gassed Power Number of 4 – 5.5 and is very mechanical strong suitable for high RPM and high viscous liquids.

Smith turbines is a high efficiency agitator for very high gas dispersion applications. Characterized by symmetrical curved pipe sections mounted to a round disc resulting in low Power Number and increased efficiency. The model ST6 has an un-gassed Power Number of 2.8 - 3.2.

Bakker turbine is a high efficiency agitator for very high gas dispersion applications and uniform dissolved gas distribution is achieved throughout the vessel. Characterized by asymmetrical curved blades mixing radial with dual asymmetrical axial flow performance. The model BT6 has an un-gassed Power Number of 2.5 being by far the best available turbine.