Thermal Mass Flowmeters

Thermal Mass Flowmeters

Thermal mass flowmeters measure gas mass flow using the thermal dispersion principle: heat is removed from a heated sensor as gas flows past, and the energy required to maintain a defined temperature difference is proportional to mass flow. Many designs use two temperature sensors - one as a reference for gas temperature and one heated element - to establish a stable “zero-flow” baseline and track cooling as velocity increases.

This approach delivers direct mass flow and temperature outputs without requiring separate pressure or temperature compensation for many control and monitoring tasks. Thermal technology is often selected where high turndown and low pressure losses are important in gas metering, providing a practical alternative to traditional techniques for process control and utility accounting.

Benefits typically include multivariable output (mass flow plus fluid temperature), strong low-end sensitivity, and quick reaction to flow fluctuations. High turndown ratios - commonly cited up to 100:1 for suitable applications - support a single meter covering both base-load and low-flow conditions without frequent range changes or bypass strategies. Insertion-style designs extend these advantages to very large pipelines and rectangular ducts while keeping installation costs predictable.

Typical applications are centered on industrial gas services such as compressed air consumption and distribution, carbon dioxide for beverage production and chilling, argon in steel production, nitrogen and oxygen production, and natural gas for burner and boiler control. Air and biogas measurement in wastewater facilities is also common, particularly where consumption monitoring, leak detection, or distribution-network surveillance is a driver.

Selection considerations include gas composition and variability (since heat capacity and thermal conductivity influence calibration), operating temperature limits, and the presence of moisture or condensable components that can alter heat transfer. Installation should provide representative velocity profiles and avoid locations that promote liquid carryover or heavy fouling. Where composition changes are expected, configuration and verification practices should explicitly account for gas-property shifts to maintain measurement integrity.

Field Instruments & Controls, Inc. an exclusive authorized representative of sales and service for Endress+Hauser.