How this calculator works
Nominal detention time, also called hydraulic retention time, equals working liquid volume divided by steady volumetric flow. Use usable liquid volume rather than total structural capacity. Area times depth gives volume for a tank of constant cross-section. Short-circuiting, mixing and dead zones mean an actual residence-time distribution can differ from this nominal value.
Formula
t = V/Q; V = A h; Q = V/t.
Worked example
A 1000 L tank at 1 L/min has a nominal detention time of 1000 min. A 20 m2 tank filled to 3 m at 10 m3/h gives 6 h.
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Frequently asked questions
Are detention time and hydraulic retention time different here?
They use the same nominal liquid volume-to-flow calculation and are combined on this page.
Should I use peak flow?
Use the flow condition being assessed. Peak and average flows give different nominal detention times.
Does this determine required treatment time?
No. Process design also depends on kinetics, mixing and the applicable design criteria.