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Thermal TA

Thermal mass flow rate measurement: Instruments for gases and mass flows

Thermal TA

Thermal TA

The measurement and analysis of flow play a central role in numerous technical applications regarding efficiency, safety and process quality. Höntzsch's thermal flow meters allow precise measurement of mass flow rates of gaseous media. The meters are based on the thermal flow measuring method which is characterized by high accuracy, long-term stability and easy handling.

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How does a thermal mass flow sensor (hot-wire anemometer) work?

The measurement principle is based on heat transer between a heated sensor element and the flowing medium.  An electrically heated wire transfers heat to the passing gas and cools down in the process. The change in electrical resistance is measured and converted into mass flow rate.

The advantage lies in the direct measurement of mass flow since no complex compensation for temperature and pressure is required. Unlike mechanical flow meters with moving parts, thermal systems operate without wear and are therefore particularly low-maintenance. 

What types of designs are available for thermal flow measurement?

Insertion probes can be used flexibly thanks to their simple installation and can be used in pipes with diameters as small as 25 mm. Installation and removal are performed using probe guide pieces; in pressurized pipelines additionally with ball valves.

The TA10 models respond even to very low flow velocities and can be used reliably at extreme values of over 200 Nm/s. They are designed for operating pressures up to 50 bar and, depending on the model, cover temperature ranges from -20 to +240° C. 

For smaller pipe diameters, inline sensors are used, which operate with inside diameters between 8 and 53.1 mm, measurement ranges from 0.04 to 1196 Nm³/h and extremely low measurement uncertainties. The temperature range here is also -20 to +240° C at pressures up to 50 bar. Custom solutions are available at any time.

Many models already include integrated transducers. Data can be transmitted via WLAN/WiFi, allowing analysis using any internet-enabled device. Additionally, interfaces such as two 4-20 mA analog outputs, media temperature output as well as bus systems like M-Bus or Modbus TCP are available.

What advantages does thermal flow measurement offer?

Thermal mass flow meters measure mass flow directly, eliminating the need for additional pressure or temperature sensors and significantly simplifying the measuring chain. This also increases the accuracy of the results. 

The devices are highly sensitive to low flow velocities and reliably measure even the smallest gas volumes. Since they have no moving parts, they are wear-free, durable and require minimal maintenance. Their use as calorimetric flow meters highlights the versatility of the measuring method.

Furthermore, Höntzsch's flow sensors are approved for use in hazardous areas (ATEX, CSA). They can also be sterilized with hydrogen peroxide (H2O2) for example as part of CIP and SIP processes.

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What types of media can be used using thermal flow measurement?

Thermal measuring devices are particularly suitable for clean, dry and pure gases. 

  • Air and compressed air - for consumption measurement, leak detection and energy management
  • Process and fuel gases - natural gas, city gas, propane (C3H8), butane (C4H10), methane (CH4)
  • Industrial gases - nitrogen (N2), carbon dioxide (CO2), oxygen (O2), argon (Ar), helium (He)
  • Specialty gases - sulfur hexafluoride (SF6) for leak testing, ethyne (C2H2) for welding applications
  • Biogenic gases - landfill gas and biogas for monitoring energy and environmental processes
  • Future energy sources - hydrogen (H2) for industrial and energy applications

The most common fields of application for thermal sensors are for example:

  • Consumption quantity measurement for energy monitoring, energy management and in facility operations
  • Fixed and portable consumption quantity measurement in air and different clean gases
  • Detection of leaks in process plants
  • Performance monitoring of compressors
  • Aeration air in wastewater treatment tanks/nitrification tanks
  • Measurement of very low flow velocities
  • Laminar flow applications in clean rooms, laboratories, under fan-filter-units, in production areas of the pharmaceutical (glove boxes); food-processing- and semiconductor industry (isolators)
  • Monitoring of settling velocity for example in the automotive industry (paint booths)
  • For high-precision gas mass flow proportional measurements such as in engine test benches, climatic chambers, combustion control and supply burner air
  • Aerospace, on ships and boats

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Multigas applications and their areas of application

Thermal mass flow meters can be configured to measure various gases without requiring complex adjustments to the device. 

With the latest sensor generations, the same device, optionally equipped with M-Bus, can be used in hazardous areas category 3G and 3D (zones 2 and 22) without requiring recalibration or return to the manufacturer. This means that a single base unit is sufficient, simplifying handling during operation and storage.

The ability to easily switch between gases allows use even in systems with varying requirements. In addition, additional gases can be integrated at any time as special characteristics that are based on a real-gas calibration in our in-house laboratory. If you're interested we are happy to assist you with any further questions.