A thermal mass flow meter measures the mass flow rate of air and gases directly, using the principle of heat transfer. Because it responds to the mass of the gas rather than its volume, it does not need separate pressure and temperature measurements to calculate mass flow. That makes it a practical and accurate choice for monitoring gas usage, controlling combustion, and managing energy costs in industrial facilities. AMETEK LMS offers thermal mass flow measurement through the Magnetrol® Thermatel® TA2, built for reliable performance in demanding process conditions.

How Thermal Mass Flow Measurement Works

A thermal mass flow meter consists of a transmitter and a probe with two temperature sensors (RTDs) located in the pins at the bottom of the probe. One sensor measures the process temperature, while the other is heated to a specific temperature above it. As gas flows past the probe, it carries heat away from the heated sensor through convective heat transfer. The higher the flow rate, the more heat is removed.

Manufacturers use one of two methods to turn this heat transfer into a flow measurement. Some keep the power constant and measure the changing temperature difference between the sensors. Others vary the power to hold the temperature difference constant. The Magnetrol Model TA2 uses the second method, measuring the power required to maintain a constant temperature difference between the sensors. The relationship between that power and the mass flow rate is established during calibration.

Advantages of Thermal Mass Flow Meters

In gas applications, thermal mass flow meters offer several advantages over differential pressure and mechanical flow meters:

• Direct mass flow measurement without separate pressure and temperature inputs
• High accuracy and repeatability at low flow rates and low pressures
• No moving parts, which reduces wear and maintenance
• Simple installation, with insertion probes for larger pipes and flow body designs for smaller lines

Common Applications for Thermal Mass Flow Meters 

Thermal mass flow meters are commonly used to measure:

• Compressed air consumption
• Natural gas flow to boilers, burners, and heaters
• Combustion air
• Digester gas and biogas in wastewater treatment
• Process gases in chemical and petrochemical facilities

They are widely used in industries such as chemical processing, oil and gas, wastewater treatment, and power generation, where accurate gas flow data supports energy management, emissions reporting, and environmental compliance.

Frequently Asked Questions

Why measure mass flow instead of volumetric flow?

Gas volume changes with temperature and pressure, but mass does not. Measuring mass flow gives a consistent reading of how much gas is actually being used, which is what matters for combustion control, energy tracking, and emissions reporting.

Can a thermal mass flow meter measure liquid flow?

Thermal mass flow meters such as the TA2 are designed for air and gas. For liquid flow detection, thermal dispersion switches and mechanical flow switches are typically used.

What is the difference between a thermal mass flow meter and a thermal dispersion switch?

Both use the same heat transfer principle. A thermal mass flow meter provides a continuous flow rate measurement, while a thermal dispersion switch provides an alarm or switch point when flow, level, or interface conditions reach a set point.