# Method of determining volume of water in an arbitrary container

by snwright
Tags: arbitrary, container, determining, method, volume, water
P: 305
 Quote by abrewmaster Going back to phyzguy's idea though about the flow meter concept, couldn't you monitor how much you put into the tank and then also monitor how much is leaving the tank as you empty it to keep a running total? That could work as well.
Horrible idea on a boat. You'd report a massive hull leak as a full tank. :)
P: 305
 Quote by Travis_King Or, use an air compressor with metering to determine how much air it takes to pressurize the tank to some pressure when empty. Fill the tank, use the compressor to maintain tank pressure. As the tank empties, the air fills the void and is metered. As a known quantity of air has entered the tank, a known volume of water must have exited.
A modification of this idea that does away with the need for a metering compressor:

Inject a tiny but accurately known aliquot of a gas into ullage space (not that hard; e.g. use a autoinjector with a microsyringe or a vial or something similar) . Wait.

Choose gas so that it is innocuous, stable, insoluble in water & whose concentration is easily measured. That won't be so hard: Thermal conductivity, IR spectra, ionization and lots of ways to very accurately detect a gas concentration.

You know conc. and moles injected. You can easily estimate ullage volume and hence the liquid volume.

After a reading a blower can easily exhaust the probe molecule to be ready for next measurement. Alternatively just use a step change in conc. after pre measurement of baseline concentration.
 Thanks P: 1,309 Use a powered “syringe” cylinder to inject 1 litre of air into the tank while the tank is sealed. (Equivalent to reducing the air volume by one litre). Monitor the step change rise in pressure. That is an inverse function of airspace volume. Subtract that from the tank volume to get the fluid volume. Measure the initial tank volume using the same device before filling the tank.
 HW Helper Thanks P: 5,591 I don't see why someone wouldn't want to inject a radioisotope into his drinking water. The nerve of some people. Think of all the new friends you would make as you bring your 'hot' boat into new ports for the first time! I'm sure the Japanese and the folks in NZ would be glad to see you!

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