Thermal mass flow meters are widely used to measure gas flow in industrial processes, environmental monitoring systems, and emissions applications. Because they measure mass flow directly, they can provide reliable readings without requiring separate pressure or temperature compensation.
However, not every thermal mass flow meter is suitable for every gas. Accurate measurement depends on the type of gas, its composition, and the extent to which that composition changes during operation.
Fox Thermal mass flow meters are designed to measure dry air and gases, including a broad range of pure gases and industrial gas mixtures.
What Types of Gases Can Thermal Mass Flow Meters Measure?
Thermal mass flow meters can measure many gases commonly found in industrial facilities. These include pure gases with a consistent composition, as well as mixed gases composed of several individual gas components.
Gases available for gas mixtures in Gas-SelectX® gas selection menus may include:
| Air | Ammonia | Pentanes |
| Argon | Chlorine | Hexanes |
| Butane | Carbon monoxide | Heptanes |
| Carbon dioxide | Propadiene | Octanes |
| Ethane | Iso Butane | Nonanes+ |
| Ethylene | Ozone | Difluoromethane |
| Helium | Iso Pentane | Sulfur hexafluoride |
| Hydrogen | Methanol | Sulfur dioxdie |
| Methane | 1-butyne | Nitrous Oxide |
| Natural gas | Benzene | Pentafluoroethane |
| Nitrogen | Water | Tetrafluoroethane |
| Oxygen | Acetone | Trifluoroethane |
| Propane | Decane | Chlorodifluoromethane |
| Propylene | Ethanol | Hydrogen sulfide |
Other common flow measurement uses of thermal mass flow meters:
- Compressed air Monitoring
- Biogas and digester gas
- Landfill gas
- Flare gas
- Vent gas
- Liquefied petroleum gas, including propane, butane, and propane-butane mixtures
The correct meter configuration depends on the specific gas being measured and the conditions of the application.
Measuring Pure Gases
Pure gases contain one primary gas component with a relatively stable composition. Air, methane, carbon dioxide, propane, and butane are common examples.
When a thermal mass flow meter is configured for a pure gas, the instrument uses the known thermal properties of that gas to calculate its mass flow rate. Selecting the correct gas is essential because different gases transfer heat differently.
A meter configured for air, for example, should not automatically be assumed to provide accurate readings for methane or carbon dioxide. The meter must account for the thermal characteristics of the actual gas moving through the pipe.
Fox Thermal meters equipped with Gas-SelectX® allow users to select from available pure-gas configurations directly within the meter. This makes it easier to match the instrument to the gas used in the application without replacing the meter or returning it to the factory for a different gas configuration.
Measuring Mixed Industrial Gases
Many industrial gas streams are not made up of a single gas. Natural gas, biogas, flare gas, vent gas, landfill gas, and liquefied petroleum gas can all contain multiple components.
For example, biogas may contain varying amounts of methane, carbon dioxide, and other trace gases. Flare and vent gas composition can also change as operating conditions, process streams, or production activity change.
These variations can make mixed-gas measurement more challenging. Because thermal mass flow measurement depends on the gas’s heat-transfer properties, a change in composition can affect the meter’s response.
Fox Thermal models with Gas-SelectX® allow users to define custom gas mixtures within the meter. By entering the individual gas components and their percentages, users can configure the meter for the mixture being measured.
When the process composition changes, the gas mixture settings can be adjusted to better reflect current operating conditions.
Why Gas Composition Matters
A thermal mass flow meter works by measuring how much heat is carried away from a heated sensor by the moving gas. Since every gas has different thermal properties, the relationship between heat transfer and flow rate changes depending on the gas composition.
This means accurate thermal mass flow measurement requires the meter to be configured for the gas or gas mixture in the process.
Applications with a stable gas composition are generally more straightforward. When composition changes, users may need to update the selected gas or custom mixture to maintain measurement accuracy.
Gas-SelectX® gives users greater flexibility to make these adjustments within the meter rather than relying on a single fixed gas calibration.
Find the Right Flow Meter for Your Gas Application
Choosing the right thermal gas mass flow meter starts with understanding the gas you need to measure and how its composition may change over time. Fox Thermal has extensive experience measuring pure gases and complex industrial gas mixtures across oil and gas, wastewater, biogas, and other demanding applications.
Contact us for help evaluating your gas composition, measurement requirements, and application conditions, or explore our gas mass flow meters to find a solution for your process.
