Thermal Mass Flowmeters

Thermal Mass Flowmeters

Thermal mass flowmeters provide direct mass flow measurement for gases by sensing heat transfer from a heated element to the flowing medium. They are often selected when high turndown and low pressure loss are important, supporting applications ranging from process control to consumption/supply monitoring, leak detection, and distribution network oversight. Insertion-style designs extend the method to very large pipelines and even rectangular ducts.

The thermal measuring principle is based on convective cooling: heat is drawn from a heated body as fluid flows past. Typical designs use two RTD elements (e.g., PT100): one measures fluid temperature as a reference and the other is heated to maintain a constant temperature differential at zero flow. As flow increases, cooling increases, and the electrical power required to maintain the differential becomes a direct measure of mass flow.

Because mass flow is measured directly, thermal meters can avoid separate pressure and temperature compensation in many gas services, while also providing the fluid temperature as an additional variable. High turndown (on the order of 100:1), strong low-end sensitivity, and fast response to flow fluctuations make the technology effective for both steady-state monitoring and dynamic utility loads.

Common applications include compressed air consumption and distribution, carbon dioxide use in beverage production and chilling, argon in steel production, nitrogen and oxygen production, natural gas for burners and boiler control, and air or biogas measurement in wastewater facilities. These duties often prioritize energy visibility, loss detection, and reliable measurement across wide operating ranges.

Selection considerations include gas composition effects (calibration is typically tied to a specific gas or mixture), contamination risk on the sensing element, and installation geometry for insertion probes (immersion depth, profile, and access for maintenance). Condensing or wet gas streams may require special attention to avoid coating or thermal lag that can bias readings. Where long-term utility accountability is required, pairing the meter with validation diagnostics and periodic verification practices helps sustain confidence in reported consumption.

George E. Booth Co., an exclusive authorized representative of sales and service for Endress+Hauser.