What is the principle of operation of thermal flow meters?

Both thermal and Coriolis flow meters measure mass flow. However, thermal meters measure mass flow quite differently than Coriolis meters. Instead of using fluid momentum, as do Coriolis meters, thermal flow meters make use of the thermal or heat-conducting properties of fluids to determine mass flow. While most thermal flow meters are used to measure gas flow, some also measure liquid flow.

Hot-wire anemometers consist of a heated, thin-wire element, and are very small and fragile. Hot-wire anemometers were used in velocity profile and turbulence research. Because they are susceptible to breakage and to dirt, they are not suited to industrial environments. Industrial thermal flow meters use a similar concept of measuring the speed of heat dissipation to determine mass flow, but use more rugged sensors that are better adapted to industrial environments.

There are several different thermal flow meter technologies. Some measure the speed with which heat that is added to the flowstream disperses. Others measure the temperature difference between a heated sensor and the ambient flowstream. Thermal flow meters typically require one or more temperature sensors to measure the fluid temperature at specific points.