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Special Report: Convective heat transfer - Use of thermal mass flow meters

by Arabian Oil & Gas Staff on Aug 30, 2017


Natural gas fuel flow is one of the most prevalent applications for thermal mass.
Natural gas fuel flow is one of the most prevalent applications for thermal mass.

Facing increased regulatory, environmental, social and bottom-line demands, today's professionals require strategic energy management solutions. Magnetrol® thermal mass flow meters improve the efficiency and safety of many processes.

Magnetrol Thermatel® TA2 ther-mal mass flow transmitter pro-vides reliable mass measurement for air and gas flow applications. The powerful, yet easy to use, electronics are contained in a compact explosion proof enclosure. The TA2 is available with both insertion probes as well as flow body design for smaller pipe sizes. The TA2 offers excellent performance at an exceptional value.

Thermatel TA2 thermal mass flow meters are up to the challenge of the most demanding applications. TA2 thermal mass flow meters will help optimise the green energy initiatives by improving measurement of greenhouse gases and making processes less energy intensive and more energy efficient.

Thermal mass flow measurement

Thermal flow meters are primarily used in air and gas flow measurement applications.  The meters consist of a transmitter and probe with temperature sensors located in the pins at the bottom of the probe.  One sensor measures the process temperature and the other sensor is heated to a specific temperature above this. As the flow rate increases, heat gets taken away from the heated sensor.

Some manufacturers use a variable power operation to keep the temperature difference constant, while others keep the power constant and measure the temperature difference. The Magnetrol Model TA2 measures the power it takes to maintain a constant temperature difference between the sensors. This relationship between power and mass flow rate is established during calibration.

Similar to thermal flow meters, the thermal dispersion flow / level / interface switches are based on heat transfer. One sensor is at the process temperature and the other is being heated by a constant power. As the flow rate increases, the temperature difference between the sensors decreases.

A set point is established; so, when that specific temperature difference is reached, the relay changes state. This can be on either increasing or decreasing flow or flow / no flow. When used in a level or interface application, it is primarily the thermal conductivity of the fluid that will provide the difference in heat transfer.

Periodically, Tom Kemme, product manager, Magnetrol, answers questions about flow meters in the Magnetrol flow portal’s ‘Ask the Expert’ column. The following are two of the recent Q&As from this column:

Will thermal mass flow meters be affected by changes in the composi-tion of gas?

Thermal mass flow meters measure a flow rate based on convective heat transfer. Fluid properties are some of the many factors that influence convection. Each gas has unique properties, which is why these flow meters are calibrated for a specific application. You would not want a meter calibrated for an air application placed into a natural gas application without recalibration or some type of field adjustment if applicable.

All gas mixes are not created equal. If you had a gas mix with high hydrogen content, a variation in hydrogen would have a much greater effect than typical variation in natural gas content. Hydrogen has a tendency to create more heat transfer than most gases. For natural gas, it is common to have some slight variation in composition between the calibration of the device and the application itself. However, the effect is minimal for slight changes in methane or ethane at different times of the year. Natural gas fuel flow is one of the most prevalent applications for thermal mass.


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