Watch particles collide and grow into flocs inside a stirred tank in real time. Track velocity gradient G, Gt (the Camp number), power density, and floc size together.
Parameters
Mixing power P
W
Effective mixer power. Higher power raises velocity gradient G and collision frequency.
Volume V
m3
Effective basin volume. For the same power, a larger volume lowers G.
Viscosity mu
mPa s
Water dynamic viscosity. Colder water is more viscous, lowering G for the same power (~1.0 at 20°C).
Contact time t
min
Total mixing time. It drives Gt = G·t, the cumulative shear that grows flocs.
Results
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Velocity gradient G (1/s)
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Gt value (Camp number)
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Power density (W/m³)
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Energy input (kJ/m³)
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Floc size (relative)
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Elapsed time (min)
Stirred-tank particle aggregation
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Floc-size growth curve
G vs floc size / break-up
Theory & Key Formulas
$$G=\sqrt{\frac{P}{\mu V}},\qquad Gt=G\,t$$
$G$: velocity gradient [s⁻¹], $P$: effective mixing power [W], $\mu$: water dynamic viscosity [Pa·s], $V$: effective volume [m³], $t$: contact time [s]. $G$ is the square root of the viscous dissipation per unit volume $P/V$ divided by viscosity, i.e. the mixing intensity (shear rate). The product $Gt$ (the Camp number) is dimensionless and indexes the cumulative shear a floc receives. Rapid mix uses high $G$ (500–1500 s⁻¹) to disperse coagulant nuclei; flocculation drops to low $G$ (10–70 s⁻¹) to grow large flocs. Too high a $G$ shears flocs apart, so the balance between collision-driven growth and break-up sets the equilibrium floc size.
How to read it
Change mixing power P, volume V, viscosity μ, or contact time t in the left panel and the result cards and the stirred-tank animation update instantly. In the animation, small primary particles ride the flow and merge into flocs when they collide. Raising the velocity gradient G increases collisions but also the shear, so grown flocs break apart and shrink. At low G they grow slowly into large flocs.
The "floc-size growth curve" shows how far flocs grow over time and when they reach equilibrium (saturation). The "G vs floc size / break-up" plot puts G on the horizontal axis, drawing the achievable floc size, the high-G break-up region, and the optimal G window at a glance. The meaning of the field practice of two-stage mixing — rapid mix then flocculation — becomes clear in both numbers and animation.
Coagulation, flocculation, and the G value
Turbid colloids carry a negative surface charge and repel one another, so they do not settle on their own. Adding a coagulant (PAC, alum, etc.) neutralizes the charge so particles can stick once they approach — this is coagulation. The water is then stirred gently so particles collide and grow into visible flocs, which is flocculation. The collision frequency is governed by the velocity gradient $G=\sqrt{P/(\mu V)}$, a measure of mixing intensity.
The product of $G$ and contact time, $Gt$ (the Camp number), is a dimensionless measure of the cumulative shear a floc receives. Too small a Gt means too few collisions and undersized flocs; too large breaks flocs apart by shear. Water treatment therefore uses a two-stage layout: a rapid-mix stage (high G, short time) to disperse floc nuclei, and a flocculation stage (low G, long time) to grow them large.
Learn Coagulation Flocculation G Value by dialogue
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So the G value is basically how hard you stir? The formula √(P/(μV)) doesn't quite click for me.
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Roughly, yes — it's the "stirring intensity" (the shear rate). Divide power P by volume V to get mixing energy per unit volume, divide that by viscosity μ, take the square root, and you get the velocity gradient G. Push the power slider up in the animation and the particles zip around — that's high G. More collisions, but the flocs also break more easily.
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Wait, isn't stirring harder supposed to make bigger flocs through more collisions?
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That's the interesting part. Collision frequency rises with G, but the shear also rips flocs apart. So at high G flocs shatter before they can grow, and the equilibrium size is smaller. Look at the growth curve — low G actually grows larger flocs in the end. For example, ahead of a settling basin we often drop G to around 20–50 s⁻¹.
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Then why not just use low G the whole time? What is rapid mix for?
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The instant you dose the coagulant, you need to spread the chemical uniformly through the whole tank. With low G the dosing is uneven and the nuclei become patchy. So for the first few tens of seconds you mix hard at high G (500–1500 s⁻¹) to scatter the nuclei, then drop to low G in the flocculation stage to grow them. Press the "Optimal condition" preset to land in that sweet-spot G.
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Is there a target for the Gt value? I can't tell if a number is big or small.
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For the flocculation stage, a Gt of 30,000–150,000 is one rule of thumb. Too small means under-coagulation, too large risks break-up. But confirm the final call with a jar test on the real water and with code values. Treat this tool as first-pass help for grasping which inputs matter.
Real-world applications
Coagulation–sedimentation design at water plants: first-pass sizing of power and detention time for rapid-mix and flocculation basins, and allocating the G value between the two stages.
Sensitivity checks for sewage and industrial wastewater: estimating the power increase needed to hold a target G as temperature (and therefore viscosity) changes.
Teaching and explanation: a single view that shows G, Gt, floc growth, and break-up through equation, numbers, and animation together.
Common misconceptions and cautions
"Higher G always grows bigger flocs" is false. High G raises collision frequency but also strengthens shear break-up, so the equilibrium floc size actually shrinks. Use this tool's growth curve and G–floc-size plot to see that non-monotonic behavior.
Contact time t covers effective mixing time only; pipe detention time is not included in Gt. Viscosity μ varies strongly with water temperature, so winter operation needs more power to hold the same G.
FAQ
Start with Velocity gradient G and Gt value. Then use G value over contact time to confirm the assumed state and Mixing-energy breakdown to read distribution or bias. Use the main plot to read the controlling trend, including break points that a single result card can hide.
Move Mixing power P alone, then move Volume V by a comparable amount and compare the change in Velocity gradient G. P/V-viscosity Gt map shows combinations where margin or performance changes quickly.
No. A higher G raises the collision frequency, but shear also breaks flocs apart. In practice you disperse the floc nuclei with high G (500–1500 s⁻¹) during rapid mix, then drop to low G (10–70 s⁻¹) during flocculation to grow large flocs. The animation shows break-up at high G and growth at low G.
G has units of s⁻¹ and contact time t has units of s, so the product Gt is dimensionless. It represents the cumulative shear a floc receives; for flocculation a Gt of roughly 30,000–150,000 is a common target. Too low means under-coagulation, too high risks floc break-up.
This simplified model captures the main relationship only. Boundary conditions, losses, nonlinear effects, and code-specific corrections still need separate checks. Final decisions still require standards, measured data, detailed analysis, and vendor limits.
How to Use
Enter mixer power input in watts (typical range 100–5000 W for treatment basins).
Specify basin volume in cubic meters (e.g., 50 m³ for rapid mix, 200 m³ for flocculation).
Input water dynamic viscosity in mPa·s (1.0 mPa·s at 20°C for freshwater).
Set contact/mixing time in minutes (the slider is in minutes; rapid mix is roughly 0.25–0.5 min, i.e. 15–30 s).
The simulator computes velocity gradient G (s⁻¹), the dimensionless Gt value, power density (W/m³), and energy input, and the stirred-tank animation visualizes floc growth and break-up.
Worked Example
Design rapid mix for a 100 m³ clarifier with a 2 kW motor, water viscosity 0.9 mPa·s, contact time 180 s: power density = 2000 W / 100 m³ = 20 W/m³. Velocity gradient G = √(20 / 0.9×10⁻³) ≈ 149 s⁻¹. Gt = 149 × 180 ≈ 26,800 (adequate for alum coagulation, target 5,000–30,000). Energy input = 2 kW × 180 s = 360 kJ.
Practical Notes
Rapid mix requires G = 500–1500 s⁻¹ (Gt ≈ 5,000–30,000) to disperse coagulant nuclei; flocculation uses G = 10–70 s⁻¹ (Gt ≈ 30,000–150,000) to preserve floc structure.
Viscosity varies with temperature: ~0.65 mPa·s at 40°C, ~1.5 mPa·s at 10°C; adjust calculations for seasonal water conditions.
Verify motor power rating and impeller efficiency; mechanical loss reduces effective power by 10–20% in paddle mixers versus centrifugal systems.