Comparison of PIV and LDA Measurement Methods Applied to the Gas-Liquid Flow in a Bubble Column

In this work a comparison of multiphase PIV and LDA measurement methods is made. The objective of the work is twofold: to provide measurement results that can be used to validate multiphase CFD simulations and to assess the different acquisition and analysis methods in multiphase measurements. The former is done with the use of a two-camera PIV/LIF method. It is shown that this method gives detailed information about the flow, without prior knowledge of the shape, size or position of the dispersed phase. The latter objective is accomplished by comparing two-camera PIV/LIF measurements with both LDA and single camera PIV measurements. With single camera PIV, it could not be decided which phase really is measured. Accordingly, an algorithm, which can distinguish the tracer particles from the dispersed phase, is needed. The sample period of 300 s for the LDA measurements appeared to be too short to obtain steady time averaged data. The simultaneous PIV/LIF velocity measurements of the gas and the liquid phase in a bubble column show a core-annulus flow. The slip velocity between the two phases is varying between 0.05 and 0.2 m s. The highest velocity fluctuations in the liquid phase are found in the axial direction and are in the order of 0.15 m s. * To be presented at: 10th Int. Symp. on Appl. of Laser Techniques to Fluid Mech., Lisbon, Portugal, July 10-13, 2000.