What is a Thermal Flow Meter?

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  • Written By: Jordan Weagly
  • Edited By: Angela B.
  • Last Modified Date: 19 January 2020
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A thermal flow meter can be any of an assortment of devices meant to measure the speed of a mass as it passes through a closed space, usually a pipe. As a mass moves through a closed space, a thermal flow meter detects the flow rate by measuring the heat transferred from the surface of the sensor to the flowing mass. These types of sensors depend on the rule that as the velocity changes so does the effect of a mass on measurement sensors.

Sensors in a thermal flow meter many times create heat using some external source of electricity. As gas molecules pass by the sensors, they take some of that heat away along with the rest of the mass in the closed space. The electricity needed to maintain a baseline temperature will reflect the mass flow from a directly proportional relationship. Useful for many applications, a thermal flow meter might be most useful for measuring the flow rates of various gases during extraction operations.


Though there are many different configurations for thermal flow meters, two can be considered the most important and widely used. One important configuration is known as the immersible thermal flow meter. It is in direct contact with the flowing mass and may include two sensors. One sensor measures the temperature of the mass and the other attempts to maintain a constant temperature. The difference between the two sensors indicates something called the thermal sensing principle, which is directly proportional to the mass flow velocity.

Another configuration of a thermal flow meter is the capillary-tube design. In this configuration, the thermal sensor is considered to be inline, meaning it is directly connected to the closed space. The sensor then measures the amount of heat convected overall to the flowing mass. Both immersible and capillary-tube sensors rely on the thermal sensing principle, which has such a high accuracy that it can be applied to many situations.

For instance, a thermal flow meter can help in research by providing precise flow rates for various types of gas. Flow meters are also potentially useful in industrial and commercial applications such as gas storage and distribution operations. The rate of flow is an important part of many operations related to the manufacturing, distribution and use of inert or combustible gas. A thermal flow meter can also provide valuable data for civic operations such as wastewater aeration or natural gas distribution.


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