Mass Flowmeter – Principles And Uses Of Mass Flowmeters

Mass flowmeters are used to measure the mass flow rate of a gas or liquid. They are used in many applications and industries, where accurate readings of the mass flow rate of a particular fluid is needed. The mass flowrate is generally measured in kilograms per second. A common application where accurate information on the flow rate of gases is needed is in the semi conductor industry. 

The other way for flowmeters to measure the flow rate is volumetric in meters3 per second. In terms of gases, a mass flowmeter is more robust as volumetric flowmeters cannot account for changes in pressure or temperature of the gas and become inaccurate. However, if the temperature and pressure of the environment are known, the mass and volumetric flow rates can be calculated from each other.

There are a few technologies used to create a mass flow meter. The most common are the thermal dispersion flow meter and the coriolis or inertial flowmeter.

Thermal dispersion mass flow meters work on the principle of measuring the change in temperature of a gas or liquid that passes through a pipe or tube. A heating device is positioned in the pipe and two temperature sensors. As the fluid or gas passes through the pipe it will be heated by the heating element.

The temperature at a point near the element and then farther along the pipe is take. If things like the density and specific heat of the fluid are known the mass flow rate can be calculated. This is done by the flow meter and returned as an analog or digital (or both) reading.

Coriolis mass flowmeters work on the principle that the forces inherent in a flow of liquid or gas will exert pressure on the tube or pipe that it is passing through.

When this tube is set to vibrate at a known frequency there will be a change in frequency when the fluid passes through. The difference or change in frequency of the tube can be used to determine the mass flow rate of the fluid passing through.

These two types of flow meters have a number of benefits. They give extremely accurate measurements. These devices use a sensor, much like an ultrasonic flowmeter, as opposed other types of meters that have a float or other mechanism that interferes with flow. Whilst this improves the accuracy of measurement, it also means that there is less chance of failure or malfunctioning occurring.