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ICLASS 97
Proceedings of the Seventh International Conference on Liquid Atomization and Spray Systems

ISBN Druckformat: 89-950039-2-8

Entrained Water Atomization Experiments and Its Size Measurements Using Optical Measurement Techniques

Abstrakt

This paper describes water entrainment measurements for twin-fluid atomization of air and water, for annular flow based upon a hydrodynamic development length of 228 with a tube diameter of 32 mm. The water and air flow rates considered were in the range 12.5-92.92 kg/m2c and 25.43-82.21 kg/m2s respectively. The data has been compared with previous results gathered by Sheriff (1993) and Teixeira (1987). This comparison shows a significant difference in entrainment flow rates, especially for the lower gas flow rates. At higher gas flow rates the entrained water data is in much closer agreement, for the lower water mass flow rate. These differences may be due to the different experimental rig configurations, although the entrainment and breakup mechanisms would not indicate otherwise. The water atomization generated a wide range of droplet size. Theses droplet sizes were measured using advanced optical techniques based on light scattering and light diffraction concepts. Phase Doppler Anemometry (PDA) provides both the diameter and velocity of individual droplets, whilst the Malvern instrument gives an ensemble droplet diameter. Results based on both diameters will be presented in terms of number mean diameter (D10) and Sauter mean diameter (D32). As the gas mass flow rate increases both D10 and D32 decrease as expected. The ratio of D32 to D10 is observed to be 1.5. Droplet measurements using PDA system were performed using a collection scattering angle of 70°, using both a 300 mW and a 2 W argon-ion laser. The results show the influence of laser power and also demonstrate a wider droplet range and appreciable difference, of up to 100%, in comparison with The Malvern measurements. The latter measurements take account of the influence of vignetting which is an inherent feature associated with this type of measurement facility. Special design of optical head employed in order to reduce this effect. Since modern CFD simulations rely upon accurate input data it is important to highlight these experimental differences, early droplet diffraction measurement found in the published literature make no allowance for the influence of vignetting.
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