Rushton Turbine Torque Calculation - D, H, Viscosity, RPM

In summary, the impeller needs to be chosen for the tank size, the motor power, the RPM, and the position. The impeller must also fit within the dimensions of the tank.
  • #1
Mechstudent
2
0
Hi;
In one of my projects I need a Rushton impeller to be used for mixing applications.
However, these kinds of impellers are quite expensive(400$ for a 2inch impeller) if bought from laboratories equipment manufacturers.
The price tag would be fine with me if only one blade was needed, but this is not the case, as my project involves many small units(around 15-20), totaling over 6000$ just for the blades, if we exclude shafts,motors,coupling and etc..

Hence why i'd like to make "Homemades" impellers. Problem is, I can't quite figure how to calculate the torque caused by the liquid on the blades.

Here's the known informations:
-The impeller is placed inside a cylindrical tank
-We know the diameter/heigth of the tank(let's assume D:10cm and H:20cm)
-The viscosity of the liquid is known(suppose 35cp)
-The RPM of the shaft(Ajustable between 0 to 250 rpm)
-The position of the impeller from the bottom of the tank(5 cm)

What I'd need to calculate is the forces acting on the impellers blade to find the proper length x heigth x thickness to properly mix the liquid(They don't bend or break)

The small diameter d on the picture and the dimensions of the blades are to be chosen;
Rushton.png
 

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  • #2
The drive power is heavily dependent on viscosity and tank design. An impeller as small as you describe will not need much power, especially at less than 250 RPM. Do you have a motor to drive that impeller? A small 12 volt cordless drill would be way overpowered for this application, but that's better than underpowered.

I hope your tanks have baffles, because without baffles you will just spin the contents without mixing. Here's a couple of links: http://www.dynamixinc.com/optimal-tank-design, and https://pdfs.semanticscholar.org/1c22/080e15418eda8b076eb8bfe6f0a0c0d0bee2.pdf.
 

Related to Rushton Turbine Torque Calculation - D, H, Viscosity, RPM

1. What is the Rushton turbine torque calculation used for?

The Rushton turbine torque calculation is used to determine the amount of force required to rotate a Rushton turbine in a liquid medium. It is commonly used in chemical engineering and fluid mechanics to optimize the design and operation of mixing tanks and reactors.

2. How is the Rushton turbine torque calculated?

The Rushton turbine torque is calculated using the formula: T = 0.5 * ρ * D^5 * N^2 * k, where T is the torque, ρ is the density of the fluid, D is the diameter of the turbine, N is the rotational speed in revolutions per minute (RPM), and k is a dimensionless constant dependent on the type of impeller and the geometry of the mixing vessel.

3. What parameters are needed for the Rushton turbine torque calculation?

The parameters needed for the Rushton turbine torque calculation include the diameter of the turbine (D), the density of the fluid (ρ), the rotational speed (N), and the dimensionless constant (k). In addition, the height of the liquid in the mixing vessel (H) and the viscosity of the fluid (η) may also be required depending on the specific application.

4. How does the viscosity of the fluid affect the Rushton turbine torque calculation?

The viscosity of the fluid has a direct impact on the Rushton turbine torque calculation. Higher viscosity fluids require more torque to rotate the turbine, while lower viscosity fluids require less torque. This is because the viscosity of the fluid affects the resistance to flow and therefore the amount of force needed to rotate the turbine.

5. What factors can influence the accuracy of the Rushton turbine torque calculation?

There are several factors that can influence the accuracy of the Rushton turbine torque calculation. These include variations in the dimensions of the turbine and mixing vessel, changes in the properties of the fluid such as temperature or density, and the presence of baffles or other obstructions in the mixing vessel. It is important to carefully consider and account for these factors when using the torque calculation for practical applications.

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