We present a technique for the measurement of the 2D distribution of the line-average void fraction in a transparent, gas-liquid flow, based on the attenuation of visible laser light by the gas bubbles in the flow. The technique is demonstrated in a test chamber of rectangular cross section. Bubbles are generated by flowing air through twenty holes in the side of a tube at the bottom of the chamber. The collimated beam of an Ar-ion laser traverses the test chamber through front and back Lexan walls, is refocused onto a pinhole and imaged with a CCD camera. Mie scattering by the air bubbles causes a spatial modulation of the laser beam, with the distribution of the logarithm of the light intensity linearly proportional to the distribution of the line average of the interfacial area density. The images are normalized against background non- uniformities and the interfacial area density calculated from the 2D transmittance distribution. The bubble diameter is estimated from the contours of the interfacial area density field and the line-average void fraction is calculated is estimated from the contours of the interfacial area density field and the line-average void fraction is calculated from the product of the interfacial area and bubble diameter fields. The results compare very favorably with measurements of volume-average void fraction based on the swell of the water level consequent to the air injection.

Date Published: 21 November 1997
PDF: 12 pages
Proc. SPIE 3172, Optical Technology in Fluid, Thermal, and Combustion Flow III, (21 November 1997); doi: 10.1117/12.279764

Published in SPIE Proceedings Vol. 3172:
Optical Technology in Fluid, Thermal, and Combustion Flow III
Soyoung Stephen Cha; James D. Trolinger; Masaaki Kawahashi, Editor(s)