Laser ultrasonic for measurements of velocity distribution in pipes

 

M. Navarrete¹, F. Hernández², J. Morales² & M. Villagrán-Muniz³

 

¹ Instituto de Ingeniería, Edificio 12, Sección de Ing. Mecánica Térmica y Fluidos, UNAM, A. P. 70-472, Coyoacán, C.P. 04510, México, D. F.

² Facultad de Ingeniería, UNAM, A.P. 70-258 C. P. 04511, México, D.F.

³ Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Laboratorio de Fotofísica, UNAM, A.P. 70-186, México, D. F.

 

Received: January 15^th, 2003.
Accepted: March 26^th, 2003.

 

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.

Keywords: Velocimetry; Turbulent pipe flow; Laser-induced blast waves.

 

Resumen

El presente trabajo describe el desarrollo de un velocímetro fotoacústico para fluidos utilizando deflectometría. El sistema de medición está basado en la detección de un pulso acústico, producido por la absorción de un pulso láser (30 ns, 1.1 mJ) que es enfocado en una línea de corriente del flujo. La propagación del pulso es registrada, aguas arriba y aguas abajo, mediante dos haces continuos que sufren una deflexión cuando interactúan con la onda acústica que es detectada por un fotodiodo rápido. De esta manera, el perfil de velocidades de una tubería de sección cuadrada es encontrado mediante el tiempo de arribo del pulso acústico medido en su sección transversal, aplicando el modelo de onda de choque cilíndrica desarrollado por Vlasses. Los perfiles obtenidos con los valores experimentales son comparados con dos modelos de flujo turbulento aplicados en tuberías.

 

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Acknowledgements

We are grateful to Instituto de Ingeniería UNAM, and DGAPA- UNAM for the financial support of this work provided by grants 2115 and IN1 12402-3, respectively.

 

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