What is a Rapid Mix Tank?

A rapid mix tank, often referred to as a flash mixer, is a critical component in water and wastewater treatment plants. Its primary purpose is to quickly and uniformly distribute chemical coagulants (like alum or ferric chloride) into the raw water stream. This process initiates the destabilization of colloidal particles, a prerequisite for effective flocculation and sedimentation.

How to Use This Design Calculator

To use the Rapid Mix Tank Design Calculator, you need to input specific hydraulic and physical parameters. Start by entering the Design Flow Rate in cubic meters per hour. Next, specify the Detention Time—typically between 10 to 60 seconds depending on the chemical used. The Velocity Gradient (G-value) represents the intensity of mixing; common values range from 600 to 1000 s⁻¹. Finally, input the water temperature to adjust for dynamic viscosity, as colder water requires more power for the same mixing intensity.

Key Engineering Considerations

When designing these systems, engineers focus on the "Gt" value (the product of velocity gradient and time). For rapid mixing, Gt values usually fall between 20,000 and 60,000. Additionally, the physical dimensions are often designed as square tanks to prevent short-circuiting and dead zones. Our calculator assumes a square cross-section to provide the most efficient hydraulic profile.

Frequently Asked Questions (FAQs)

What is the typical detention time? Most flash mixers are designed for 30 seconds of contact time. Why is temperature important? Temperature affects the viscosity of water. As water gets colder, it becomes more viscous, requiring more motor power to achieve the same G-value. Can I use this for circular tanks? While this tool calculates based on a square footprint, the volume remains the same; you would simply adjust the diameter for a circular configuration.