Thermal mass flowmeter (TMF) is a direct mass flow meter based on the principle of heat diffusion, mainly used for mass flow measurement of gas or liquid. Its core principle is to calculate the mass flow by measuring the cooling effect of the fluid when it flows through the heating element, or the temperature change of the fluid after absorbing heat.

I. Working principle

1. Application of heat conduction law

- The sensor contains two reference-level temperature sensors: one as a heating element (velocity sensor) and the other to detect the fluid temperature (temperature sensor). When the fluid flows, it takes away heat, resulting in a temperature difference signal between the two sensors, which is proportional to the mass flow rate.

- Flow calculation is achieved through the constant temperature difference method (maintaining a constant temperature difference between the heating element and the fluid) or the constant power method (fixed heating power, measuring temperature difference changes), without the need for temperature or pressure compensation.

II. Key structures and technical features

1. Design without moving parts

- The sensor has no mechanical moving parts, strong vibration resistance, high reliability and low maintenance requirements.

2. Wide range and high precision

- The range ratio can reach 100:1 or even 1000:1, which is suitable for low flow rate (such as 0.01 m/s) to large pipe diameter scenarios, and the accuracy is usually ±0.5%~3%.

3. Material and adaptability

- The liquid contact parts are made of corrosion-resistant materials (such as 316L stainless steel, alloy C22), supporting high temperature (up to 500℃), high pressure (PN 40) and corrosive media.

4. Installation flexibility

- Insertion type: suitable for DN80~6000mm pipelines, pressurized installation (through ball valve).

- Pipe section type: factory pre-calibrated, used for small pipe diameters or high-precision scenarios.

III. Main application areas

1. Industrial gas monitoring

- Natural gas, hydrogen, and fuel gas metering, compressed air flow control, and semiconductor manufacturing process gas management.

2. Environmental protection and energy

- Biogas recovery, flue gas emission monitoring, and sewage treatment aeration flow control.

3. Special scenarios

- High temperature gas (such as kiln gas supply), corrosive media (such as chlorine), and small flow leakage detection.

IV. Advantages and limitations

- Advantages:

- Direct output of mass flow, no temperature and pressure compensation required;

- Low pressure loss design, low energy consumption;

- Fast response speed (2-10 seconds).

- Limitations:

- Limited applicability of liquid measurement (only small flow scenarios);

- Changes in medium thermal conductivity may affect accuracy.

Thermal mass flowmeters have become the mainstream choice for gas flow measurement in industrial process control with their simple structure, fast response and wide range advantages, and continue to expand the technical boundaries in the field of liquid micro-flow.