Top‐Hat Beam Technique: Improvements and application to bubble measurements

Abstract
A new‐generation velocimeter/sizemeter is described. Size measurement is based on the top‐hat beam technique. Velocity measurement is carried out by using laser Doppler velocimetry. Advantages and limitations of the top‐hat beam technique are discussed and compared with other techniques (pedestal, visibility, phase Doppler). Bubble diagnosis in a turbulent pipe flow is reported.