Thermal mass flowmeters are most commonly used to measure the mass flow of clean gases, such as air, nitrogen, hydrogen, helium, ammonia, argon, and other industrial gases. Mixtures, such as flue stack flow and biogas flow, can be measured when their composition is known. An advantage of this technology is its dependence on thermal properties that are almost independent of gas density.
Be careful when using thermal flowmeters to measure the flow of gases with unknown and/or varying composition, such as hydrogen-bearing off-gases and other mixtures that can disproportionately affect the thermal flowmeter measurement. Thermal mass flow meters are used almost entirely for gas flow applications.
As the name implies, thermal mass flow meters use heat to measure flow. Thermal mass flow meters introduce heat into the flow stream and measure how much heat dissipates using one or more temperature sensors. The amount of heat loss from the sensor is dependent upon the sensor design and the thermal properties of the fluid.
The thermal properties of the fluid can (and do) vary with pressure and temperature, however, these variations are typically small in most applications. In these applications where the thermal properties of the fluid are known and relatively constant during actual operation, thermal flow meters can be used to measure the mass flow of the fluid because the thermal flow measurement is not dependent upon the pressure or temperature of the fluid.
However, in many applications, the thermal properties of the fluid can be dependent upon fluid composition. In such applications, varying composition of the fluid during actual operation can affect the thermal flow measurement. Therefore, it is important for the thermal flow meter supplier to know the composition of the fluid so that the proper calibration factor can be used to determine the flow rate accurately.
Suppliers can provide appropriate calibration information for other gas mixtures, however, the accuracy of the thermal flow meter is dependent on the actual gas mixture being the same as the gas mixture used for calibration purposes. In other words, the accuracy of a thermal flow meter calibrated for a given gas mixture will be degraded if the actual flowing gas has a different composition.
|Sage Metering is your source for monitoring and controlling the gas mass flow in your manufacturing process, building management system or environmental application. Our high performance, NIST Traceable, Thermal Mass Flow Meters will help increase productivity, reduce energy costs, maximize product yields, and/or help reduce environmental insult. Sage provides high-quality In-line and Insertion Thermal Mass Flow Meters for a wide variety of industrial, commercial, and environmental monitoring needs, including carbon credit verification for Greenhouse Gas Reduction.|