Diffusion & Mixing Time Estimator

Calculate mixing time and assess diffusive mixing in microchannels

Input Parameters

Diffusion Coefficient (m²/s)

D = 1.00e-9 m²/s

Channel Width (µm)

Channel Length (µm)

Flow Velocity (µm/s)

Results

Diffusion Time

5000.00 ms

Péclet Number (Pe)

0.100

Diffusion dominated (good mixing)

Required Mixing Length

0.01 mm

for full diffusive mixing

Residence Time

10000000.00 ms

✓ Mixing is COMPLETE

Residence time (10000000.00 ms) ≥ diffusion time (5000.00 ms)

About Microfluidic Mixing

Mixing in microfluidics depends on diffusion and advection. The Péclet number (Pe) quantifies their relative importance.

Diffusion Time: t_diff = w² / (2D) — time for a molecule to diffuse across the channel width by diffusion alone.

Péclet Number: Pe = Uw / D — ratio of advective to diffusive transport.

Mixing Length: L_mix = Pe × w — the minimum channel length needed for two streams to fully mix by diffusion.

Mixing Assessment:

• Diffusion dominated (Pe < 1): Good passive mixing
• Transitional (Pe 1-10): Moderate mixing, may need longer channels
• Advection dominated (Pe > 10): Poor passive mixing, consider active mixing

Microfluidics enables excellent mixing compared to macroscale devices due to small channel dimensions, but high flow velocities can suppress it.

Disclaimer: This calculator assumes simple binary diffusion in laminar flow. Actual mixing performance depends on channel geometry, flow profile development, temperature gradients, and multi-component interactions. Always validate with experimental measurements or CFD simulation.

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