Low cost thermal transient anemometer for challenging gas flow rate measurements

Abstract

Few commercially available gas flow rate measurement devices can be employed in applications with strict pressure drop allowances, high working pressures, or corrosive working fluids. Additionally, most measurement approaches (e.g., turbine, rotameter, thermal dispersion) have limited turn-down ratios, generally less than 50. Here, a new economical and mechanically simple thermal transient anemometer design is proposed and evaluated for internal gas volumetric flow measurement. The flow meter operates through cyclical electrical heating and convective cooling of a thermocouple probe. Flow rates are correlated with average cooling-period temperatures. Heating and cooling profiles are dynamically adjusted during operation, permitting relatively good accuracy and a large turn-down ratio (450). The objective of this investigation is to model, design, and demonstrate the operation of the anemometer using air as working fluid. The anemometer has a measurement range of 0.5–226.5 l min−1 with free stream temperatures varying between 22–26°C. A segmented numerical model, which includes the varying heating loads and velocity profiles in the working fluid, is developed and validated.