Volumetric flow rate measurements in oscillating pipe flows with a laser-Doppler sensor

Abstract

The authors deal with a measuring technique for low flow rate measurements. They describe a sensor that uses a laser-Doppler anemometer as the basic measuring technique to yield instantaneous flow rate information. The principle of the measuring device is explained and it is shown that the axial velocity of a pipe flow can be utilised to obtain the volumetric flow rate. If information on the velocity profile shape is readily available, no calibration of the instrument is required. Using this measuring principle in conjunction with the high measuring precision of laser-Doppler anemometry allows a highly precise instrument to be designed and built for flow rate measurements. The authors show that this instrument has also the capability to carry out instantaneous flow rate measurements. Time-averaged and instantaneous flow rates can both be measured, the latter up to a limiting frequency given by the pipe diameter and the viscosity of the fluid.