Why wet gas cannot be measured with thermal gas mass flowmeter？

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Thermal gas mass flowmeter is a common device used to measure gas flow. Its principle is based on heat conduction and cooling effects. However, when it comes to wet gases, thermal gas mass flow meters may no longer be suitable, sparking curiosity and exploration.

Before we deeply understand why wet gases are not suitable for thermal gas mass flowmeters, let’s briefly understand the principle of this flowmeter. Thermal gas mass flow meters determine the mass flow of a gas by measuring the transfer of heat from the fluid through a sensor. As the gas passes through the sensor, a heating element on the sensor surface provides heat energy, while the sensor on the other side measures the heat being conducted away. Based on the amount of heat conducted, the mass flow rate of the gas can be inferred.

However, the presence of wet gases can interfere with the accuracy of thermal gas mass flow meters. Humid gases contain water vapor, and water vapor has a higher ability to conduct heat than other gases. This means that when moisture passes through a thermal mass flow meter, the water vapor absorbs more heat, resulting in a smaller heat transfer value measured by the sensor. Since the flowmeter determines mass flow based on heat conduction values, this interference will cause deviations in the measurement results.

In addition, the water vapor in the moisture may also condense on the sensor surface. When water vapor comes into contact with the sensor surface, since the sensor is usually at a lower temperature, the water vapor condenses into liquid water and accumulates on the sensor. This prevents heat from being efficiently conducted to the other side of the sensor, further affecting the accuracy of the measurement results.

Therefore, due to the influence of humid gas on heat conduction and cooling effects, thermal gas mass flow meters have certain limitations when measuring moisture. To solve this problem, other types of flow meters have been developed, such as wet gas mass flow meters and ultrasonic gas mass flow meters, which are more accurate and reliable in measuring moisture.