Measuring water flow is easy – all you need is one of the various water flow meters that are out there on the market today. And even if you don’t have one, it’s easy to get your head around the concept of water flow rates with a bucket and a tap. Crank on the tap, press ‘go’ on the stopwatch, and press ‘stop’ when it’s full.
If your 5 litre bucket filled up in 30 seconds, simply divide 5 by 0.5, and that’s your flow rate – 10 litres per minute.
More specifically, this is called the volumetric flow rate, or the ‘volume’ of water passing through a point over a certain amount of time. In other words, it’s how fast water is moving in your pipes, which is crucial information for a huge number of different industrial and commercial applications – for product quality, safety, optimisation of operations, environmental reasons, and so much more. Although there are more sophisticated technologies nowadays, the most basic water flow meter for volumetric flow consists of a mechanical turbine or paddle wheel which rotates at a proportional rate to the actual flow.
However, another technique for calculating water flow is by detecting differential pressure, with the help of a pressure-based flow meter. This type of water flow meter introduces a restriction to the flow, which creates a differential pressure between the upstream and downstream sections of the flowing water. This method is more efficient than a standard flow sensor when the rate of flow is very low, or if the water is dirty or contains contaminants.
Yet another way to get that flow rate calculation done is by honing in on the fluid’s thermal properties – with a thermal flow meter. It works by introducing a set amount of heat to the application, with the result that the temperature is lost as it is transferred to the liquid. The faster the flow, the more heat is lost, and if it all sounds unnecessarily complex, the truth is that it is among the most accurate and repeatable ways to measure flow. Another highly accurate and vastly-different way to measure flow rate is with ultrasonic waves, which work a little like sonar based on how long the pulses take to bounce between sensors.
But if the application requires highly-reliable flow measurements not only for water and fluids but also gases and steam, the vortex shedding principle may be a better way to do those complex calculations. This type of water flow meter works by monitoring the behaviour of oscillating vortexes introduced to the water or gas. The frequency of the complex ‘vortex shedding’ phenomenon is proportional to the volume flow.
Next up, if you thought that volumetric flow rate formula was tricky, consider the mathematical representation of how electromagnetic flow meters work:
e = k * B * ν * d
It all relies on something called Faraday’s Law of Induction, where the creation of a magnetic field to a flow scenario will mean proportionately more or less voltage depending on how fast that liquid is flowing. “e” is the voltage reading, “k” is the constant, “B” is the strength of the magnetic field, and “v” and “d” are the conductor’s velocity and length respectively. The only issue is that because pure water does not conduct electricity, the fluid in question will have to be one that contains ions – including tap, ground, and wastewater.
As is hopefully obvious, water flow may sound simple – but there are actually plenty of ways to skin a cat. The water flow rate calculation method and meter required for your organisation depends solely and specifically on the goals, variables and conditions of your particular application, so always consult with an experienced industry expert for guidance.
