Laser ultrasonic for measurements of velocity distribution in pipes

Abstract

The present work describes the development of a photoacoustic flowmeter with probe-beam deflection. A pulsed laser beam produces an acoustic pulse, whose propagation is registered by its deflection effects on two cw probe beams. The acoustic pulse in a flowing fluid is produced by absorption of a laser pulse (30 ns, 1.1 mJ) focused over a path flow line. The acoustic propagations, along and against the flow, are monitored by two cw probe beams. In the interaction, the probe beam undergoes a transient deflection that is detected by a fast response photodiode. The velocity distribution data profile of a square pipe is obtained by means of the acoustic pulse arrival time measured through its cross section applying the cylindrical shockwave model developed by Vlasses. The profiles determined with this experimental technique are compared with two turbulent pipe flow models.