Experimental phase-Doppler anemometry

This procedure has been used to determine droplet size in sprays. Oseillations in the curve relating x and D can be smoothed out by the use of an incident laser beam having a broad speetral bandwidth [83]. An accumulation of independent scattering intensities from multiple scatterers ean be used to measure the mean droplet size of a group [84]. This procedure has been applied to water sprays and the experimental data confirmed by phase Doppler anemometry [85]. The applicability of the polarization ratio technique is strongly influenced by the complex refractive index of the dispersed media and is limited to media having a relative refractive index below about 1.44 [86]. 

Bertola F, Grundseth J, Hagesaether L, Dorao C, Luo H, Hjarbo KW, Svend-sen HF, Vanni M, Baldi G, Jakobsen HA (2005) Numerical Analysis and Experimental Validation of Bubble Size Distribution in Two-Phase Bubble Column Reactors. Multiphase Science Technology 17(1-2) 123-145 Breim G, Braeske H, Durst F (2002) Investigation of the unsteady two-phase flow with small bubbles in a model bubble column using phase-Doppler anemometry. Chem Eng Sci 57(24) 5143-5159... 

Various flow visualisation techniques have been utilised to obtain experimental results from local gas hold-ups and bubble size distributions (BSD) in a gas-liquid mixed tank. Particle Image Velocimetry (PIV), Phase Doppler Anemometry (PDA), Capillary suction probe (CSP), High-speed video imaging (HSVI) and Electrical Resistance Tomography (ERT) techniques have been applied. The applicability of various techniques is dependent on the location of the measurement, the physical properties of the gas-liquid flow, the gas hold-up and the size of the tank. 

A series of experiments has been carried out in the group of G. Brenn, TU Graz, Austria, for water sprays and PVP/water (20% PVP and 80% water by mass) sprays in air with different liquid mass inflow rates [42]. Various atomizers with different dimensions of swirl chambers and exit diameters were used. At various cross-sections, the droplet sizes and velocities are recorded for different liquid inflow rates using phase Doppler anemometry (PDA) [52]. The present simulations concern the experimental data using the Delavan nozzle SDX-SD-90 with an internal diameter of 0.002 m and an outer diameter of 0.012 m at the nozzle throat and 0.016 m at the top [42]. The liquid inflow rates for water/air spray are 80kg/h and 120 kg/h, and a 112 kg/h flow rate is used for the spray of a PVP/water solution in air. The spray is injected into a cylindrical spray chamber with a diameter of 1 m. The carrier gas is at standard conditions. Measurements are taken at cross-sections of 0.08 m, 0.12 m, and 0.16 m away from nozzle exit. The experimental data at the closest position to the nozzle is used to generate initial data for the numerical computations [53]. 

Since 1995 the experimental work has been concentrated on preparation of the second phase of investigations in water (WAMIX II) and providing a comparable testing arrangement in sodium (NAMIX experiment). For measurements of local velocity (see Fig. 1) and temperature as well as their fluctuations in the WAMIX test-section, laser Doppler anemometry and resistance thermometry are applied in a modified test-section. To make these measuring techniques applicable, some modifications on the water loop were also made. 

During the last four-five decades, the laser-Doppler anemometry (LDA) has become a commonly used experimental technique to measure the instantaneous velocity of seeded single phase flows, and dispersed two-phase flows of very low concentration. A major reason is that LDA is a non-invasive optical technique and does not disturb the flow. Moreover, the LDA system has a high spatial resolution with a fast dynamic response and range. 

Our understanding of the hydrodynamics of multiphase flows has progressed substantially in the recent three decades, thanks to the development of advanced experimental techniques, particularly laser Doppler anemometry (LDA), particle image velocimetry (PIV), computer-automated radioactive particle tracking (CARPT), and optical bubble probes. In addition, computational fluid dynamics (CFD) simulations allow for inner views in two-phase process equipment. 

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