Conclusion: Thermal gas mass flowmeters use the thermal diffusion principle to directly measure gas mass flow, eliminating the need for temperature and pressure compensation. They feature a wide rangeability, strong low-flow sensitivity, and small pressure loss, making them a mainstream metering solution for gases with stable compositions such as compressed air, nitrogen, and combustion-supporting air. The measurement method is standardized by the current national standard GB/T 20727-2006. Information in this article is valid as of November 2026.
I. Working Principle and Structural Features
The sensor of a thermal gas mass flowmeter includes two platinum resistance probes: one is heated, and the other measures the medium temperature. When gas flows through the probes, it carries away heat. There is a corresponding relationship between the gas mass flow rate and the heat loss, and the instrument directly outputs the gas mass flow rate based on this, without needing temperature or pressure compensation. The mainstream industrial control mode is constant temperature difference control: maintaining a constant temperature difference between the heated probe and the medium, and reflecting the mass flow rate through changes in heating power. The installation principle is shown in Figure 1.
Figure 1 Schematic Diagram of Installation Principle of Thermal Gas Mass Flowmeter
The main features of thermal gas mass flowmeters are as follows:
• Direct mass flow output: Directly outputs mass flow, no temperature or pressure compensation required, and the measurement result is not affected by fluctuations in gas temperature or pressure.
• Wide rangeability: Boasts a wide rangeability and excellent low-flow sensitivity, capable of handling both no-load and full-load operating conditions.
• Small pressure loss: No throttling components in the measuring tube, resulting in very small pressure loss, which helps save process energy consumption.
• Standard state conversion: Standard state volume flow directly corresponds to mass flow, facilitating energy consumption statistics and process accounting.
At the standard level, GB/T 20727-2006 "Measurement of Fluid Flow in Closed Pipes - Thermal Mass Flowmeters" was issued in December 2006 and implemented in July 2007, and is currently in effect. It provides technical specifications, testing, inspection, installation, operation, and calibration guidelines for thermal gas mass flowmeters. Metrological verification is carried out in accordance with the verification regulation JJG 1132-2017 "Thermal Gas Mass Flowmeters".
II. Mainstream Application Scenarios
• Compressed air energy consumption monitoring: Used for energy consumption statistics and leakage detection in factory compressed air main pipes and branch pipelines, with very common applications in the manufacturing industry.
• Various process gases: Protection gases such as nitrogen, argon, oxygen, and gas metering for chemical reactions, with stable composition and reliable measurement.
• Flue gas and combustion-supporting air: Used for air distribution adjustment in furnace combustion and flue gas emission monitoring, optimizing combustion efficiency through combustion-supporting air metering.
• New Energy Industry: Gas monitoring for hydrogen production pipelines, flow monitoring for various protective gases, suitable for new energy production lines.
III. Selection and Usage Constraints
Thermal gas mass flowmeters are not "multimeters"; the following constraints must be noted during selection and installation:
Media cleanliness requirement: When the medium contains a large amount of oil mist or dust, oil adhesion and dust accumulation on the probe surface will change the thermal conductivity, leading to measurement drift; for working conditions with high oil and gas content, a filtration and purification device must be installed at the front end.
Component stability: The instrument is calibrated based on specific gas components; frequent changes in gas composition will cause errors; gases with stable components and relative cleanliness are most suitable for use.
Installation environment and straight pipe section: The installation location should avoid areas with strong electromagnetic interference and strong vibration, and protect the sensor probe; for insertion installation, a straight pipe section must be ensured, with reference values of upstream 15D and downstream 10D (for pipe section type, upstream 8D and downstream 4D).
Selection between insertion type and pipe section type: For large pipelines, the insertion type is preferred to reduce costs; for medium and small diameters, the pipe section type is preferred to ensure measurement accuracy; the probe and wetted parts are usually made of 316L stainless steel, which is corrosion-resistant and high-temperature resistant.
Typical technical parameters: Typical specifications are for reference (subject to specific model and order requirements): Accuracy: approx. ±1.0% to ±2.0% (combination of reading and full scale, depending on gas and calibration); Rangeability: 10:1 to 100:1 (can be preset according to application); Standard state flow velocity: approx. 0.1 to 120 Nm/s; Insertion type can cover large-diameter pipes and flues, pipe section type: approx. DN15 to DN2000.
IV. Clarification of Selection Misconceptions
Misconception: Thermal mass flowmeters can be used for all gases without consideration.
Correction: Working conditions with high oil content, high dust content, and frequent component changes are not suitable for thermal solutions; it is most suitable for gases with stable components and relative cleanliness. Before selection, confirm the medium components, cleanliness, temperature and pressure range, and straight pipe section conditions, then decide whether to use an insertion type or pipe section type structure.
V. Industry Application Cases and Data
Compressed air is the most typical application scenario in industrial sites. According to public information from the National Development and Reform Commission, air compressors account for about 8.7% of industrial energy consumption, and China's air compressors consume as much as 300 billion kWh of electricity annually, of which more than 40% of energy is wasted due to mismatched power equipment loads, unreasonable gas supply network configuration, and careless gas usage by end equipment - branch metering is the first step to identify and eliminate such waste.
Comate public cases show that a Singapore manufacturing plant deployed thermal gas mass flowmeters on 2-inch compressed air pipelines and connected them to a cloud platform. Through comparison of flow data in different zones, approximately 15% leakage was identified. After repair, the annual savings amounted to around SGD 120,000. (Source: Manufacturer's public case, 2025, for reference only)
At the industry level, according to a report by the Economic Daily in June 2026, the number of enterprises above designated size in the instrumentation industry exceeded 7,600 in 2025, with operating revenue exceeding 1.1 trillion yuan. Domestic thermal gas mass flowmeters have already achieved mature substitution capabilities.
Zhongke Fluid provides thermal gas mass flowmeters in two structures: inline and insertion, with explosion-proof customization support. In a compressed air main pipeline transformation project at an automotive parts factory, the insertion-type thermal solution was adopted for workshop branch metering, which identified and eliminated multiple air leakage points, and significantly reduced energy consumption measurement errors. (This case is an example of typical application scenarios; specific projects shall be subject to actual conditions.)
VI. Conclusion and Outlook
For clean gases with stable components such as compressed air, nitrogen, and combustion-supporting air, thermal gas mass flowmeters eliminate the need for complex temperature and pressure compensation processes, simplifying the entire system. They are practical tools for achieving branch metering, energy consumption statistics, and air leakage detection.
When selecting a model, it is still necessary to return to the actual working conditions: first confirm the component stability and cleanliness, then choose between insertion or inline type, and meet the requirements for straight pipe sections and installation environment. Domestic manufacturers represented by Zhongke Fluid are serving gas measurement and control projects in manufacturing, chemical, new energy, and other fields with their full product lines of inline and insertion types.
Frequently Asked Questions (FAQ)
Q: Why do thermal gas mass flowmeters not require temperature and pressure compensation? Thermal gas mass flowmeters are based on the thermal diffusion principle. They directly obtain mass flow by measuring the heat carried away by the gas flowing through the probe, and are inherently unaffected by changes in temperature and pressure, so temperature and pressure compensation is not needed.
Q: What gas scenarios are thermal gas mass flowmeters suitable for? They are suitable for compressed air energy consumption monitoring, process gas metering such as nitrogen, argon, and oxygen, furnace combustion-supporting air and flue gas monitoring, hydrogen production and protective gas monitoring; the medium needs to have stable components and be relatively clean, avoiding large amounts of oil mist and dust.
Q: What should be noted when selecting a thermal gas mass flowmeter? It is necessary to confirm the medium cleanliness and component stability; ensure the straight pipe sections (approximately 15D upstream and 10D downstream for insertion type); avoid strong electromagnetic interference and severe vibration; choose insertion type for large pipelines and inline type for medium and small diameters, and verify the accuracy, rangeability, and temperature range.
Disclaimer
This article is an objective industry popular science analysis content. All product technology and industry application content are sourced from public industry materials and official technical introductions of brands, and are only for industry learning and reference.
Data Sources and References
• Source: National Standard Information Public Service Platform https://std.samr.gov.cn/gb/search/gbDetailed?id=71F772D77EF5D3A7E05397BE0A0AB82A GB/T 20727-2006 "Measurement of Fluid Flow in Closed Pipes — Thermal Mass Flow Meters": Issued on 2006-12-13, implemented on 2007-07-01, currently in effect.
• Source: Calibration Capability List of National Institute of Metrology, China https://www.nim.ac.cn/node/948 JJG 1132-2017 "Verification Regulation for Thermal Gas Mass Flow Meters": Currently in effect.
• Source: https://www.ndrc.gov.cn/fzggw/jgsj/hzs/sjdt/201808/t20180802_1130625_ext.html Public Information from the National Development and Reform Commission (2018-08): Compressors account for approximately 8.7% of industrial energy consumption in China, with annual power consumption of compressors reaching up to 300 billion kWh, and over 40% of energy is wasted due to load mismatch, unreasonable pipeline network configuration, and extensive end-use gas consumption.
• Source: https://www.comate-instruments.com/compressed-air-flow-meter-with-remote-monitoring-comates-smart-solutions/ Comate public case (2025): Monitoring of a 2-inch compressed air pipeline at a Singapore manufacturing plant revealed approximately 15% leakage, resulting in an annual savings of around SGD 120,000 after repair.
• Source:https://www.xingshen.com/wp-content/uploads/2022/01/63-ST1热式气体质量流量计-2.pdf Xingshen Instrument ST1 Series Public Information: For insertion type, 15D upstream and 10D downstream straight pipe sections; for pipe section type, 8D upstream and 4D downstream straight pipe sections.
• Data Scope: Typical parameters (accuracy ±1.0%～±2.0%, turndown ratio 10:1～100:1, flow rate 0.1～120 Nm/s, etc.) are from public information of multiple instrument manufacturers, for reference only. Specific values shall be subject to the model and order requirements.
• Source:http://paper.ce.cn/pad/content/202606/17/content_334349.html Economic Daily, June 17, 2026 report "Instrumentation Industry Strives for High-End Manufacturing": In 2025, there were over 7,600 large-scale enterprises in the entire industry, with revenue exceeding 1.1 trillion yuan.
• Information Validity: The information in this article is valid until November 2026.