Shear Rate Calculator (RPM to s⁻¹)
Calculate the shear rate for parallel plate or concentric cylinder geometries based on rotational speed.
Understanding Shear Rate from RPM
In rheology and fluid dynamics, the shear rate is the measure of the rate at which adjacent layers of fluid move with respect to each other. When using rotational viscometers or rheometers, converting RPM (Revolutions Per Minute) to a shear rate (measured in reciprocal seconds, s⁻¹) is essential for characterizing non-Newtonian fluids.
The Calculation Formula
For a parallel plate geometry, the shear rate at the edge of the plate is calculated using the following formula:
Where:
- γ (Shear Rate): Expressed in s⁻¹.
- r (Radius): The radius of the rotor/spindle (mm).
- RPM: Rotational speed.
- h (Gap): The distance between the measuring surfaces (mm).
Why is Shear Rate Important?
Many industrial fluids like paints, polymers, and food products are shear-thinning. This means their viscosity decreases as the shear rate increases. By calculating the exact shear rate from your RPM settings, you can ensure consistent quality control and accurate scientific comparisons between different equipment setups.
Example Calculation
If you are operating a viscometer at 60 RPM with a spindle radius of 20 mm and a gap height of 1 mm:
- Convert RPM to rad/s: (60 * 2 * 3.14159) / 60 = 6.283 rad/s
- Apply radius and gap: (6.283 * 20) / 1 = 125.66 s⁻¹
The resulting shear rate experienced by the sample at the outer edge is 125.66 s⁻¹.