Thermal mass flow meters, also known as thermal dispersion or immersible mass flow meters comprise a family of instruments for the measurement of the total mass flow rate of a fluid, primarily gases, flowing through closed conduits.
Thermal flow meters are primarily used in air and gas flow measurement applications.
The meters consist of a transmitter and probe with temperature sensors (RTDs) located in the pins at the bottom of the probe.
One sensor measures the process temperature and the other sensor is heated to a specific temperature above this.
As the flow rate increases, heat gets taken away from the heated sensor in the form of convective heat transfer.