Hello friends, I hope you all are doing well. In today's tutorial, I am going to discuss What is a Thermal Flow Meter and How Does It Work? Let's begin! Thermal flow meters' main principle is to use the heat conductivity of both gases and liquids to determine its mass flow. Unlike flow meters that determine the volumetric flow rate like turbine flow meters or purge flow meters, thermal flow meters are resistant to temperature fluctuations and pressure of the substance’s pressure.
This type of flow meter can also be used for measuring gas and airflow. Thermal flow meters have varying designs that are made specifically for different situations. A few of these designs have high-pressure and high-temperature features that are more capable of dealing with these specific cases.
How Does a Thermal Flow Meter Work?
Thermal flow meters, using the thermal properties of the substance, measure the flow of a fluid flowing inside a duct or a pipe. Typically, a thermal flow meter introduces a specific amount of heat to its sensor. Some of the heat dissipates, and as the flow increases, the more heat will be lost, which will then be picked up by the sensor. With this data, the measurement of the fluid flow will then be determined.
The amount of heat that is lost in the fluid depends entirely on the design of the sensor used in the flow meter and the fluid’s properties, especially its heat conductivity. In most applications, the thermal properties of the liquid measured can vary in temperature and pressure. These varying factors are too small to make any changes in the overall measurement.
In most cases, the temperature and pressure have a fixed value. Thus, thermal flow meters can easily measure the mass flow as it is not dependent on these factors.
However, there are also times when the thermal properties of a substance can solely be dependent on the substance’s composition. This can change the outcome of the result, which, in turn, can affect the measurement of the flow rate.
With that said, the flow meter supplier needs to know the composition of the fluid so that the calibration factor will be efficient in measuring the liquid. Because of this reason, thermal flow meters are mostly used to measure pure gases.
The flow meter must have the calibration appropriate for a specific substance. But, if the material has a different composition, the accuracy of the measurement will be significantly affected.
But where can we find flow meters for sale?
Flow meters for commercial and industrial purposes are commonly available on hardware centres or shops that sell hydraulic products. These meters can be bought online too as there are online retailers that sell such products.
Principles Used in Thermal Flow Meters
When fluid enters the pipe and comes in contact with a heated object, the fluid takes away some of the heat, which will then make the fluid more heated in turn. This is the main principle that the thermal flow meter uses to determine the mass flow.
Thermal flow meters can be divided into two groups:
Temperature difference measurement method: A heater will be introduced in the stream and will be measured at two points, both upstream and downstream. The difference in their results will be used to determine the flow. This is more applicable when dealing with low flow pressure.
Power consumption measurement method: Just like the other method, it introduces a heater that will put two points in the stream, both upstream and downstream. However, the heater will maintain a fixed difference in temperature, and the amount of power that is needed to do that will be the main variable in determining the flow rate.
Applications of Thermal Flow Meters
To avoid damaging the sensor of the flow meter, it shouldn’t be used to measure abrasive and corrosive fluids. Also, avoid introducing a substance that can coat the sensor of the flow meter as it can affect the relationship of the thermal properties of a liquid and the flow meter, thus harming its measurement. When the sensor gets coated too much, it can be rendered as inoperable. Therefore, you should thoroughly clean it first before going on another operation.
Having a different percentage of the individual components in the fluid’s composition that varies from the calibrated values can cause inefficiency and inaccuracy in the flow meter’s measurement. That said, thermal flow meters aren’t applicable in measuring substance that has a varying composition.
Mostly, thermal flow meters are used to measure clean or pure gases like nitrogen, air, hydrogen, ammonia, and other industrial substances. Other fluids with a mixed composition like biogas flow and flue stack flow can still be measured, as long as their structure has been known beforehand. One advantage of thermal flow meters is that it measures the fluid using its thermal properties independent from its gas density.
Also, when dealing with corrosive or abrasive fluids, it must be emphasized that the composition of the said fluids should be known beforehand to avoid damaging the sensor, which can lead to inaccurate measurements. They are also used in petrochemical and chemical plants, to the condition that the gases that will be measured have information of the composition beforehand.
Advantages and Disadvantages
The advantages of thermal flow meters include its ability to detect and measure different gases, not having any pressure loss, and its ability to measure gas flow with known variables.
Its disadvantages are difficulty in calibrating to match the composition of the fluid that will be measured, errors that might manifest when the temperature of the fluid changes drastically and being inoperable when a composition buildup occurs in the sensor.
Thermal flow meters are one of the most preferred metering systems by many industries. It represents more or less 2 percent of the sales in flow meters in the global market. Unlike other types of flow meters that calculate the volumetric flow that requires the mass density, pressure, and other factors to measure, thermal flow meters can directly provide mass flow measurements.
Usually, thermal mass flow meters can measure and control the mass flow at a molecular level and offers a reliable and accurate analysis that is required in industrial plants.
I hope you understand all the points of thermal flow meter and how its work if you have any question related to this you can comment below and ask us. We will answer your queries. Thank you for reading it.
I am Syed Zain Nasir, the founder of The Engineering Projects (TEP). I am a
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