[nussehund]

As part of a water treatment unit I need to mix H2O2 (2.5%) with water. The H2O2/water ratio is about 1 to 100. If I add 1 unit of H2O2 to 100 units of water how long will it take for the H2O2 to be "mixed" with the water? Will it be possible to do the mixing "on the fly" by injecting small doses of H2O2 into a hose with a continuous flow of water?

Thanks
Peter

[Hunter2]

It will mix directly. You can inject it in a pipe.

[Arkcon]

There are some very advanced hydrodynamic equations for determining when a large volume of fluid is thoroughly mixed.  And I guess they're pretty important in the planning stage of chemical engineering, 'tho I'm not a chemical engineer, so I can't really help.

http://en.wikipedia.org/wiki/Navier-Stokes_equations

Often, people determine experimentally when things are mixed and go from there.  For example, one time the maintenance people wanted to chlorinate a tank, and they had a colorimetric assay for chlorine concentration, but it was "too dark" and didn't let them know just how much was there.  I told them they'd have to dilute the sample with chlorine free water, maybe serially, and that we could use the spectrophotometer to really quantify the color.  But they gave up and just let it go.

[eazye1334]

How long the mixing will take depends on a lot of other factors, specifically flow characteristics (laminar vs. turbulent) and "vessel" geometry (whether it's pipes or a batch kettle or whatever). More generally, the mixing will depend on your flow rate, cross-sectional area, and piping shape and length.