Definition of Thermal Mass Flow Meter
Thermal Mass Flow Meter uses the principle of convective heat transfer in a fluid to measure the rate of flow flowing in a pipe or channel. Generally in thermal flowmeters there are two temperature sensors.
One of the sensors is heated at a certain temperature by a circuit and serves as a flow sensor. While the second temperature sensor acts as a reference sensor, and measures after recording the temperature of the gas.
Working Principles of Thermal Mass Flow Meter
When there is a gas flowing on the first sensor (flow sensor), the flowing gas molecules transport heat from this sensor. As a result the first sensor decreases in temperature and cools, and energy is lost. This causes circuit equilibrium to be disrupted, and the temperature difference (ΔT) between the heated sensor and the reference sensor has changed.
In one second, the circuit will restore lost energy by heating the flow sensor to correct overheating temperatures. As the flow rate increases, there will be more heat on the sensor lost. Mass transmitters use the difference between these heats to determine the rate of the fluid. Most Thermal Mass flow meters are used to measure gas flow.
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The amount of heat lost from the sensor depends on the sensor design and the thermal properties of the fluid. The thermal properties of fluids vary following pressure and temperature variables, but these variations are usually small in most applications. So in applications where the thermal properties of the fluid are known and are relatively constant during actual operation, thermal type flow meters can also be used to measure mass because the fluid is independent of the pressure or temperature of the fluid.
Therefore, the Thermal Mass Flow Meter must know the composition of the fluid so that proper calibration factors can be used to accurately determine the flow rate. Because of this constraint, flow meters are usually applied to measure pure gas flow. However, in many other applications, the thermal properties of a fluid are determined by the composition of the fluid. In applications like this, the various fluid compositions during actual operation can affect the results of thermal flow measurements.
Thermal Mass Flow Meter Application
Thermal mass flow meters are widely used in various industries with a variety of different applications. The applications are grouped into energy conservation, environmental functions, industrial use and measurement with specific gases such as in nitrogen blanketing processes.
Thermal mass flow meter has the function to measure the speed of gas flow, gas temperature, gas flow rate and total mass of gas passing through the flow meter sensor. This function is displayed by a thermal mass flow transmitter that produces digital displays, data and other aoutput that can be used for control or others.
Thermal mass flow meters can be used by almost any type of gas such as air, oxygen, nitrogen, helium, argon, CNG, natural gas, CO2, and other gases.
The electrical power needed to maintain this heat is presented as a mass flow signal sent to the flow transmitter. There is no need for external temperature or pressure devices.
Also Read: Definition, Type, and Application of Flow Sensor
Superiority
The advantage of a thermal flow gauge is that it has no moving parts. It reduces maintenance and allows use in demanding application areas, including saturated gases. They also do not require temperature or pressure correction and provide excellent overall accuracy and repetition over various flow rates. This meter force calculates mass flow rather than volume and is one of several categories of meters that can measure flow in large pipes.
The flow meter distributor/vendor should provide proper calibration information for other gas mixtures. However the accuracy of a thermal flowmeter depends on the same actual gas mixture as the gas mixture used for calibration purposes. In other words, the accuracy of the thermal flowmeter calibrated for a given gas mixture would degrade if the actual flowing gas had a different composition.