Thermal Mass Flow Meters

A thermal mass flow meter is a device used to measure the mass flow rate of a gas directly. It works using thermal dispersion technology: one sensor is heated and another acts as a reference, allowing the meter to determine flow by measuring how much heat is carried away by the moving gas.

Thermal mass flow meters are widely used where dependable gas flow measurement is needed for process control, energy monitoring, compliance and operational efficiency.

A thermal mass flow meter works by maintaining a temperature difference between a heated sensor and a reference sensor. As gas flow increases, more heat is removed from the heated sensor. The instrument measures this change and uses it to calculate the gas flow rate.

Because the measurement is based on the thermal properties of the gas, thermal mass flow meters are well suited to a wide range of industrial gas applications and can provide stable, repeatable performance without moving parts.

The main benefits of thermal mass flow meters are direct gas mass flow measurement, no moving parts, wide turndown capability, low maintenance and strong performance across many gas applications.

They are often chosen for their reliability, especially in applications involving low flow rates, variable demand, or gases that may be wet, dirty or difficult for other technologies to handle. They are also available in both insertion and inline formats, making them suitable for everything from small gas lines to large industrial pipes and ducts.

Thermal mass flow meters can be used for a wide range of gases, including compressed air, natural gas, biogas, hydrogen, combustion air, flare gas and syngas.

The right meter depends on the gas composition, pressure, temperature, moisture content, line size and the demands of the application.

With the right calibration and specification, thermal mass flow meters provide reliable gas flow measurement across a broad range of industrial, energy and process environments.

Thermal mass flow meters are used in a wide range of gas measurement applications, including compressed air monitoring, natural gas measurement, biogas flow to CHP units, waste gas burners and flares, hydrogen monitoring, combustion air measurement, fuel gas injection systems, syngas lines, and large-duct gas flow measurement.

Typical applications include:

• monitoring compressed air usage to identify waste and improve efficiency
• measuring biogas flow in anaerobic digestion and renewable energy systems
• monitoring natural gas consumption in industrial processes
• measuring combustion air to support process performance
• flare gas monitoring in demanding industrial environments
• low-flow gas measurement in smaller process lines
• large pipe or duct installations where average flow measurement is critical

Our product range covers these duties from inline meters for pipe sizes from ¼" to 1½", through to insertion meters for pipes above 1½", as well as dual-sensor solutions for large diameter pipes and ducts.

Yes, thermal mass flow meters are often an excellent choice for biogas applications, especially where the gas is wet, dirty, low pressure or variable in composition.

We have been involved in numerous biogas installations where gas mass flow meters are widely used for measuring flow to CHP units, waste gas burners and flares - where reliable gas flow data is needed for control, reporting and performance monitoring.

Their no-moving-parts design also makes them well suited to more challenging biogas environments where long-term reliability is important.

An insertion thermal mass flow meter is mounted through the wall of a pipe or duct and is usually the preferred option for larger line sizes, typically above 1½".  It is often more practical and cost-effective on larger pipes.

An inline thermal mass flow meter is installed directly into the pipeline and is generally used for smaller pipe sizes, typically from ¼" to 1½", or for lower-flow duties where a dedicated flow body is more suitable.

The right choice depends on the pipe size, gas, flow range, installation constraints and application requirements.

In some cases, yes. Certain insertion models can be installed or removed under live process conditions using a full-bore ball valve arrangement. This can help reduce downtime and disruption during maintenance or replacement.

Whether live insertion or removal is suitable depends on the application, pressure, safety requirements and the specific meter selected.

Speak to our team today for advice and information for your requirements.

Choosing the right thermal mass flow meter depends on the gas, pipe size, flow range, pressure, temperature, installation layout, hazardous-area classification and the purpose of the measurement. For example:

• compressed air monitoring on larger pipes may suit an insertion meter
• low-flow gas duties may be better suited to an inline model
• large ducts or poor flow profiles may require a dual-sensor design
• harsh flare gas or offshore environments may need a more advanced industrial specification

The best starting point is to review the application in terms of gas type, operating conditions and site requirements, then match that to the most suitable meter design.

Our expert engineering team have tackled almost every scenario and are always on hand to respond to your queries.

Allison Engineering has been supplying thermal mass flow meters in the UK for over 30 years, with a strong installed base across industrial, process, renewable energy and energy management applications.

Our range covers everything from general-purpose compressed air and natural gas measurement to biogas, flare gas, hydrogen, syngas, low-flow gas lines, and large duct or pipe installations.

That breadth of product offering, combined with application knowledge and technical support, means customers can choose a solution that is suited not just to the gas, but to the realities of the process and site.