SINGLE-POINT LASER MEASUREMENTS

A method which has received considerable attention over the past 15 years is phase-Doppler anemometry (PDA) which allows determination of the size of spherical particles, droplets or bubbles. Hence, local particle size distributions and size-velocity correlations can be obtained. Moreover, recent developments provide the basis for accurate particle concentration or mass flux measurements 

Increasing interest in detailed experimental analysis of two-phase flows has led to a number of review papers on single point laser measurements. A more general overview on two-phase flow measurements was given for example by Taylor (1994) focusing on current activities in PDA development and PIV applications in two-phase flows. Applications of LDA and PDA for analyzing flows with combustion were reviewed by Heitor et al. (1993), and a more industrial orientated review on particle sizing methods can be found in Black et al. (1996). 

The dual beam configuration of LDA is most widely used today, where the Doppler difference frequency is directly measured and the receiving optics may be placed at an arbitrary position with respect to the transmitting beams. Laser-Doppler anemometry has been first applied to measurements of mean velocities and turbulence properties in single phase flows. In this case small particles, which follow the flow and the turbulent fluctuations, need to be present in the flow or must be added to it (i.e. seeding the flow with a tracer). The principles of LDA are, for example, described in detail by Durrani and Greated (1977), Durst et al. (1981), and Durst et al. (1987). 

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