Rapid Mix G-Value Calculator
Rapid mix has to disperse coagulant in seconds. Enter your mixer power, basin volume, and water temperature to get the velocity gradient G — the number designers actually specify.
Velocity Gradient
| Item | Value |
|---|
How the calculation works
Formulas
G = √( P / (μ · V) ) — P in watts, μ in Pa·s, V in m³, G in s⁻¹
μ = 2.414×10−5 · 10247.8 / (T − 140) — T in Kelvin (water viscosity–temperature relation)
1 hp = 745.7 W · 1 ft³ = 0.0283168 m³ · 1 gal = 0.00378541 m³
G = √( P / (μ · V) ) — P in watts, μ in Pa·s, V in m³, G in s⁻¹
μ = 2.414×10−5 · 10247.8 / (T − 140) — T in Kelvin (water viscosity–temperature relation)
1 hp = 745.7 W · 1 ft³ = 0.0283168 m³ · 1 gal = 0.00378541 m³
Notes & limitations
G = √(P/μV) is the Camp–Stein velocity gradient (1943), the standard rapid-mix design parameter in AWWA/ASCE Water Treatment Plant Design and Crittenden et al., Water Treatment: Principles and Design.
- Use mechanical power actually delivered to the water (shaft power), not the motor nameplate rating — nameplate overstates G.
- Typical rapid-mix design range is G = 300–1,000 s⁻¹ with detention measured in seconds. G alone does not guarantee good mixing — also check blend time and basin turnover.
- Viscosity rises sharply in cold water, so the same mixer produces a lower G in winter; verify winter operation.
- This is a design and operations screening tool. Confirm changes against jar testing and plant SOPs.
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