Flow Rate / Velocity Converter
Convert between flow rate and linear velocity in microfluidic channels. Calculate cross-sectional area, hydraulic diameter, and residence time for rectangular and circular geometries.
Parameters
Results
| µL/min | 1.000000 |
| mL/hr | 0.060000 |
| nL/s | 16.666667 |
| µL/hr | 60.000000 |
| mL/min | 0.001000 |
| mm/s | 0.003333 |
| cm/s | 0.000333 |
| m/s | 0.000003 |
| Parameter | Value |
|---|---|
| Width | 100 µm |
| Height | 50 µm |
| Cross-sectional area | 5000.00 µm² (0.005000 mm²) |
| Hydraulic diameter | 66.67 µm |
Understanding Flow Rate vs. Velocity in Microfluidics
Why Velocity Matters More Than Flow Rate
In microfluidic design, linear velocity (mm/s) is often more relevant than absolute flow rate (µL/min) because it determines how long molecules spend in the channel (residence time), controls mixing efficiency, and affects reaction kinetics. Identical flow rates in channels of different cross-sections produce different velocities—a 1 µL/min through a 50 µm × 50 µm channel creates very different residence times than 1 µL/min through a 500 µm × 500 µm channel.
Shear Stress and Fluid Dynamics
Linear velocity directly governs shear stress in the channel. Shear stress (τ) near the wall is approximated by τ ≈ µ(dv/dy), where µ is dynamic viscosity. Higher velocities increase shear stress, which can lyse cells, denature proteins, or initiate platelets. This makes velocity essential for applications involving biological samples. Cross-sectional geometry also matters: rectangular channels with high aspect ratios (long, narrow) experience higher peak shear stresses than wide, shallow ones at the same velocity.
Residence Time and Reaction Kinetics
The time a fluid element spends in a channel determines reaction extent. Residence time (τ_res) is simply channel length (L) divided by linear velocity (v): τ_res = L / v. For mixing or biochemical assays, residence times typically range from milliseconds to seconds. To extend residence time without reducing flow rate, increase channel length (serpentine or spiral designs) or cross-sectional area, maintaining low velocity.
Reynolds Number and Flow Regime
The dimensionless Reynolds number (Re = ρvDh/µ) predicts flow regime. Microfluidic channels typically operate in the laminar regime (Re < 1000), where viscous forces dominate and diffusion governs mixing. At very low Re (< 0.1), diffusion is rapid even across the channel width; at higher Re (approaching turbulence), mixing requires active strategies like chaotic advection.
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