Development of a fiber anemometer for direct measurement of low average velocity inside ducts

Abstract

A fiber anemometer for direct (without traversing) measurement of average velocities, 0<u<40 cm/s, of air in laminar flow inside ducts is developed. Three experimental configurations representing different locations of the fiber, shapes of flow cross section (circular and rectangular), and duct heating are considered. The relationship between average mass velocity and fiber deflection is established by calibration and calculations, which used a local drag coefficient for thin cylinders in laminar cross flow. The effect of velocity profile on the relationship was found to be significant. The effect of fluid temperature was also significant, and the anemometer is capable of measuring the average mass velocity only in connection with a thermometer. For the present applications, however, the uncertainty of the method due to these effects was found to be small.