1. What is the Stokes Number?

The Stokes number (Stk) is a dimensionless number that characterizes the behavior of particles suspended in a fluid flow. It represents the ratio of the characteristic time of a particle to the characteristic time of the flow.

2. How Does the Calculator Work?

The calculator uses the Stokes Number equation:

Where:

• \( \rho_p \) — Particle density (kg/m³)
• \( d_p \) — Particle diameter (m)
• \( U \) — Flow velocity (m/s)
• \( \mu \) — Dynamic viscosity (Pa·s)
• \( D \) — Characteristic dimension of the flow (m)

Explanation: The equation shows how particle inertia relative to the fluid flow depends on particle properties and flow conditions.

3. Importance of Stokes Number

Details: Stokes number is crucial in aerosol science, particle separation, and fluid dynamics. It determines whether particles follow fluid streamlines (Stk << 1) or deviate due to inertia (Stk >> 1).

4. Using the Calculator

Tips: Enter all values in SI units. Particle diameter and characteristic dimension are typically very small (microns to millimeters). Viscosity of air at 20°C is about 1.8×10⁻⁵ Pa·s.

5. Frequently Asked Questions (FAQ)

Q1: What does a high Stokes number mean?
A: High Stk (>1) means particles don't follow fluid streamlines well due to their inertia, leading to impaction or separation.

Q2: What's a typical Stokes number range?
A: In respiratory deposition, Stk of 0.01-1 is common. For industrial separators, values may range up to 10 or more.

Q3: How does temperature affect Stokes number?
A: Temperature mainly affects viscosity (μ). Higher temperature reduces μ, increasing Stk for the same flow conditions.

Q4: Can Stokes number be less than zero?
A: No, all parameters are positive quantities, so Stk is always positive.

Q5: What's the difference between Stokes number and Reynolds number?
A: Reynolds number characterizes flow regime (laminar/turbulent), while Stokes number characterizes particle behavior relative to the flow.