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Hydraulic Retention Time Calculator

Calculate nominal hydraulic retention time from working liquid volume and representative throughflow. Keep the ideal ratio separate from real mixing or treatment performance.

117 / ESTIMATE NOMINAL RESIDENCE

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INPUT GROUP 01

Working liquid inventory and flow

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Read the method and example

YOUR CALCULATION

Nominal residence time is working liquid volume divided by steady flow.

Nominal hydraulic retention (days)

2

Nominal hydraulic retention (hours)

48

Entered flow per hour (m³/h)

12.5

Nominal tank-volume turnovers per day

0.5

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How the hydraulic retention time calculator works

Nominal hydraulic retention in days = working liquid volume in cubic meters divided by throughflow in cubic meters per day. Multiplying by 24 gives hours. The tool also displays the flow per hour and the number of working tank volumes passing per day.

The volume must describe liquid held within the chosen boundary. Throughflow must describe the same system and conditions. Zero flow has no finite calculated retention time. Zero working volume with positive flow gives a zero nominal time; a zero working volume makes tank-volume turnovers undefined.

Real residence-time distributions can differ because of mixing, dead zones, short-circuiting, fluctuating flows and recirculation. Hydraulic retention is different from solids retention. The calculation does not select a basin size, process operating target, treatment capability or compliance threshold.

Worked example

A 600 m³ working volume at a representative 300 m³/day has a nominal retention time of 2 days, or 48 hours. The same flow is 12.5 m³/h and represents 0.5 working tank volumes per day. Doubling flow to 600 m³/day reduces nominal retention to 24 hours.

Sources and assumptions

The source material explains the underlying calculation or pricing structure. Entered prices, costs, schedules and scenario choices are your assumptions; this tool does not obtain supplier quotes or predict actual results.

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