Garden & outdoors
Gravity tank drain curve
Plot liquid head and outflow as a constant-area tank drains.
A clear answer. Here’s how.
Integrates the Torricelli discharge model for a tank with constant horizontal cross-section: time=2Atank(√h₀−√h₁)/(Cd Aout√(2g)). Final head is no greater than initial head. Assumes a small outlet, constant coefficient, atmospheric pressure at free surface and discharge, and unrestricted venting. Exports 101 head/flow samples; head is measured above the outlet.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Tank horizontal cross-section (m²)
- 1
- Initial head above outlet (m)
- 1
- Final head above outlet (m)
- 0
- Outlet diameter (mm)
- 20
- Supplied discharge coefficient
- 0.62
Example result
| Elapsed time (s) | Liquid head (m) | Outflow (L/min) |
|---|---|---|
| 0 | 1 | 51.7568871288 |
| 23.1853201877 | 0.9801 | 51.2393182575 |
| 46.3706403754 | 0.9604 | 50.7217493862 |
| 69.5559605632 | 0.9409 | 50.2041805149 |
| 92.7412807509 | 0.9216 | 49.6866116436 |
Constant horizontal tank area, atmospheric discharge and constant supplied coefficient. Head is measured above the outlet.