			Home About us Contact

Droplet Velocity (droplet + velocity)

Distribution by Scientific Domains

Chemistry	100%

Selected Abstracts

Prediction of Droplet Velocities and Rain Out in Horizontal Isothermal Free Jet Flows of Air and Viscous Liquid in Stagnant Ambient Air

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2007
S. Al Rabadi
Abstract Two-dimensional phase Doppler anemometer measurements of droplet size and velocity conducted under several nozzle conditions and a systematic variation of the air mass flow quality and liquid phase viscosity show that the air entrainment process is enhanced when keeping all test conditions constant except for increasing the Newtonian liquid viscosity above of that of water. A two-zone entrainment model based on a variable two-phase entrainment coefficient is proposed with the normalized axial distance allowing for a change in the jet angle. Thus, the jet perimeter is lower and the breakup length is longer in the case of air/relatively higher viscosity liquid phase. It provides the most accurate reproduction of the experimental droplet velocity in comparison with that of other models in the literature and, hence, is recommended for the prediction of the droplet velocity in the case of two-phase air/liquid phase free jet flow in stagnant ambient air. A model for predicting the droplet rain out, considering the droplet trajectories in the free jet flow, allows also for an adequate reproduction of the experimental data. [source]

Re-entrainment of wall deposits from a laboratory-scale spray dryer

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2007
M. J. Hanus
Abstract This work has determined the magnitude of re-entrainment and established the operational parameters that may be manipulated to influence re-entrainment of salt particles for a small-scale spray dryer (Buchi B-290). The wetness of the spray dryer wall deposits was found to significantly influence the magnitude of re-entrainment. It was shown both experimentally and numerically that wet deposits form at low nozzle air-to-liquid ratios (<2000), which form large droplets that dry slowly, while the initial droplet velocity did not have a large influence on wet deposition. Wet deposits form strong liquid and solid bridges, and thus deposits formed from wet particles were difficult to re-entrain. Less than 2% of deposits formed at nozzle air-to-liquid ratios less than 2000 were re-entrained, while 15.4 to 21.2% of dry deposited particles (formed at nozzle air-to-liquid ratios ranging from 2308 to 3409) were re-entrained. The threshold re-entrainment velocity of sodium chloride particles in the Buchi B-290 spray dryer was found to be between 4 and 7.7 ms,1, which is consistent with the lower-end threshold velocities presented in the literature. No significant trend relating relative humidity to the magnitude of re-entrainment was found in the 0.2,7.4% average relative humidity range, suggesting that the adhesive forces in spray dryer wall deposits are fairly constant across this relative humidity range. Decreasing wall deposit wetness through use of high (>2000) nozzle air-to-liquid ratios and use of high main gas velocities increased the re-entrainment of wall deposits in this spray dryer. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd. [source]