Laser grating technique for measurement of local velocity of large drops and jets in liquid-liquid systems

Measurement of the local rise velocity of large liquid drops of 3-7 mm in diameter and the local axial wave propagation velocity on a liquid jet surface in liquid-liquid systems were successfully performed using a Laser Grating Velocimeter (LGV). The primary frequency of the photodetector signal that is required for evaluation of the local velocity, was determined unambiguously by a frequency-domain Fast Fourier Transform analysis of the velocity signal. The validity of this technique, which eliminates potential measurement errors, was confirmed by a controlled experiment. The LGV was applied to the determination of the drop terminal rise, velocity distribution of a population of 300 drops, and axial distribution of the jet surface wave velocity in order to demonstrate the capability and effectiveness of the technique.