How Do Mass Flow Meters Work?

Flow meters are very reliable in providing accurate and precise measurements regarding fluid flow in a system.

In this article, the basic principles of how the different types of flow meter work will be briefly discussed.

Indirect Mass Flow Measurement

Indirect mass flow meters usually measure the mass flow by computing the resulting flow through the pressure and temperature measurement. These are considered indirect measurements because they use different types of sensors and a computing device in order to arrive at a mass flow measurement. These measurements are used in circumstances where a direct reading is not possible because of the inapplicability of the parameters. Volumetric flow meters are a perfect example for this type of meter. These are magnetic, differential pressure, positive displacement, Ultrasonic, non-compensated vortex, and turbine meters.

Direct Mass Flow Measurement

Direct-types of flow meters directly measure the mass of a fluid passing through the device. Measuring the mass flow directly is an effective way of ensuring an accurate reading. This will eliminate the inaccuracies resulting from the varying physical properties of fluids. These types of flow meters are not affected by pressure and temperature changes. To be able to get a measurement in this type of meter, the fluid is allowed to flow straight through a tube and onto the meter. These make direct measurement perfect for higher flow rates and lesser pressure drops.

Coriolis Mass Flow Meters

Coriolis type of flowmeter measures mass through inertia or through the effect of a moving mass on a body. The Fluid is vibrated by a small actuator and flows through a tube wherein the acceleration results in a measurable twisting force.This force is proportional to the mass flow rate of the fluid flowing through it. Other high-end variations of these meters are integrated with dual tubes for enhanced sensitivity and lessened pressure drops. These flow meters are beneficial in applications where the fluid is a variable or an undefined mixture.

Thermal Mass Flow Meter

Thermal type of mass flow meters arrive in a direct measurement that is derived from the heat transfer along the heated source. These meters have two temperature sensors and a heat source.The sensors will measure the heat transfer as the fluid passes over a pipe and  the meter will measure the rate on how quickly the fluid disperses the heat. This value will be proportional to the mass flow.

Pressure Differential Flowmeter

These types of flow meters measure fluid flow through the principle of differential pressure. The concept behind this is using an obstruction on the flow within the pipe to induce a difference of static pressure between the upstream and downstream end of the device. Based on Bernoulli’s equation, the square of the flow rate is proportional to the pressure drop across the obstruction, therefore, a high-pressure drop means a high flow rate.

Key Takeaways

Mass flow meters measure the volume or mass flow in a system and the values from these meters are often used to indicate the system efficiency and overall operationality. Different types of these meters have unique operational principles specified for different applications.

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