Thermal Mass Flowmeters

Thermal Mass Flowmeters

Thermal mass flowmeters measure gas flow by quantifying how a moving gas stream removes heat from a heated sensor element. A common implementation uses two temperature sensors: one monitors the gas temperature as a reference, while the other is heated to maintain a fixed temperature differential. As flow increases, the heated sensor cools more strongly and the instrument increases power to hold the differential; that required power is proportional to mass flow.

Because measurement is inherently mass-based, thermal meters are attractive where mass or standard volumetric flow is needed for gas management. They are often selected when high turndown and low pressure loss matter, providing an alternative to DP, vortex, or turbine meters for many utility and process-gas services. Insertion-style designs extend this capability to very large pipelines or rectangular ducts without the cost of full-bore metering.

Typical applications include compressed air consumption and distribution monitoring, CO₂ for beverage production and chilling, argon in steelmaking, nitrogen and oxygen production gases, and natural gas for burner and boiler control. Air and biogas measurement in wastewater facilities is also common, where leak detection, aeration control, or distribution-network monitoring benefits from stable low-flow sensitivity.

Implementation details drive performance: straight-run requirements are generally modest, but a representative flow profile, correct insertion depth, and compensation for gas temperature are essential. Thermal meters also respond to changes in gas properties (specific heat and thermal conductivity), so applications with varying composition should be evaluated for calibration strategy or configured gas-group compensation. Clean, dry gas services are typically the most straightforward; wet gas or particle-laden streams may require probe protection, filtration, and periodic inspection.

Selection is typically based on expected flow range, allowable pressure drop, pipe size, and whether the meter must be removable under pressure. When matched to the gas and installed to minimize condensation and fouling, thermal mass metering provides wide-range measurement that supports energy management, leak reduction, and utility optimization.

Miller Mechanical Specialties, an exclusive authorized representative of sales and service for Endress+Hauser.