How is flow measured?

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How is flow measured?
Flow rate measurement is employed widely across many industries, and is used to measure the volume of a liquid or gas passing through a specific cross-sectional area per unit of time. Flow rate measurement helps us to control and monitor the rate of liquid flow within applications and ensure that fluid control processes are running safely and cost-effectively. We will take a look at how flow is measured, some of the flow control options available and what it is important to consider when thinking about flow rate measurement.

Why is flow rate measurement important?

People have been measuring flow rates since 5000BC, with the earliest known device used by the Mesopotamians. They developed a crude plumbing system within their Sumerian cities to deliver water to each household from the nearby rivers and used flow measurement techniques to monitor the flow rate from the river into their channels. Since the early 18th century, scientists and mathematicians have been developing theories and devices which, over time, have led to the development of the technologies that we use today for flow rate measurement. These devices employ a number of different techniques and systems which allow us to monitor and control flow rates. All industries that process liquids and gases or have a requirement for fluid control use flow rate measurement tools – from utility companies measuring the flow of wastewater moving into water filtration systems, to power generation businesses requiring deionised flow measurement; from oil and gas industries measuring the rate of flow of crude oil, through to wine producers measuring the fill rate during the bottling process. Wherever fluid moves through a system, there is likely to be a need for flow rate measurement.

How is flow measurement affected by the fluid?

Within industrial settings there are a number of options available for flow rate measurement. In fact, there are over 100 different types of flow meters employed globally, each offering a different solution depending on the application parameters and other influencers such as budget. Some of these include:
  • Coriolis meters: one of the more popular flow rate measurement devices, this flow meter uses motion mechanics principles, utilising a vibrating tube that is caused to twist in proportion to the mass flow rate. This response is subsequently monitored to provide an output.
  • Magnetic flow meters: these use Faraday’s Law, whereby a magnetic field is passed through the media which is flowing through the pipe causing a voltage signal to be transmitted to electrodes. This voltage is directly proportional to the velocity of the fluid.
  • Differential pressure flow meters: a constriction is created within a pipe that results in a pressure drop. The flow meter measures this pressure drop and, using Bernoulli’s equation, calculates the flow rate on the basis that the pressure drop across the constriction is proportional to the square of the flow rate.
  • Turbine flow meters: these are mechanical flow meters that use a rotating turbine within the flow stream. This uses the velocity of the flow to rotate the turbine which sits directly in the flow, enabling a flow to be calculated using a continuity equation.
One of the most important factors to consider when looking at flow rate measurement is the type of media flow, because how flow is measured can depend on what the flow consists of. For example, gas can be measured using Coriolis, differential pressure and positive displacement flow rate measurement devices, but cannot use electromagnetic or ultrasonic flow meters. If you are looking for the right flow rate measurement tool but are unsure of which flow meter would be most suited to your application, Best Pneumatics has a range of flow sensors and switches available. For more information on how flow is measured or flow rate measurement options, contact us on 01254 390555.