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Propeller Calculator

In industrial processes it is necessary to prepare mixtures and stir them. As a concept, agitation refers to forcing a fluid by mechanical means so that it acquires circulatory movement inside the container. Mixing is the random distribution of two initially separate phases. That involves starting with two individual phases, and having both phases randomly distributed to each other.

Propela Con geométria.png

Concept area:

  • Liquid or substance height (H) - Height at which the propeller will work

  • Internal Diameter of Tank (Dt) - Diameter of the tank to which the propeller will be working.

  • Propeller diameter (Da) - It is obtained in relation to the dimensions of the tank.

  • Propeller width (W) - It is obtained from the ratio of the size of the propeller diameter in most cases es  1 : 4

  • Deflectors (K) - Also known as baffles, they are elements welded inside the tank by means of brackets that reduce fluid vortices.

EYE:

  1. If the relationship H/Dt ˃ 1 means that it opens dead zones, or points that there is no dynamics.

  2. If the H/Dt ratio is ˃ 1.5, 2 propellers will be required on the same axis 

  3. If the ratio H/Dt ˂ 0.5 it will be necessary to divide into quadrants and add agitators by quadrants or it may work to place the propeller diagonally.

Engine power

The power consumption depends on variables such as the density of the fluid (d), its viscosity (u), the force of gravity (g), the stirring speed in seconds (N), the diameter of the impeller (Da), the diameter of the tank (Dt), the height of the liquid (H), and different geometric characteristics of the system.

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Due to the complexity  of the agitation system (recipient, impeller, deflectors, diffusers, coils, etc.), obtaining an analytical equation for power calculation is complex. However, through a dimensional analysis it can be expressed as a function of dimensionless numbers:

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Power Number: 𝑁𝑃 = P  / (d*N^3*Da^5)

Reynolds number: 𝑅𝑒 = (d*N*Da^2) / u 

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The NP is a ratio between the power consumed by the agitator and the inertia that is induced in the fluid.

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The Re represents therelationship between inertial and viscous forces.

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Given the complexity of finding the power, this calculator will propose thepower number,which is obtained from tables according to the propeller or in the same way you can consult it with your provider. And finally, the rpm at which the engine will work will be placed to interpret our Reynolds number.

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EYE:

  1. Laminar regime: Re < 10 - The fluid is static or does not present mixing, distribution, dispersion or exchange of substance

  2. Transient regime: 300< Re < 10000 - The liquid is in motion with slight turbulence, it is a state where it can already present exchange and distribution of substance

  3. Turbulent regime: Re > 10000 - The liquid is in turbulence, therefore, the process of mixing and dispersing the substance throughout the tank occurs and the more this number increases, the violence of the turbulence will be greater.

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power correction

Once reached here, as a closure, the power will be adjusted in relation to our geometry of the tank and the propeller.

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This will help if the tank and propeller do not have an optimal geometric relationship. and it will allow us to have correction factors for our engine.

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