An Experimental Study of the Effect of Small Particles on the Fluid Turbulence in Fully Developed Flow of Air in a Horizontal Pipe PDF Download

Author: Lucia M. Liljegren
Publisher:
ISBN:
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Languages : en
Pages : 402

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Book Description
Measurements of the mean and fluctuating velocities of both the solid and gas phases in a dilute suspension flowing through a 5 in diameter horizontal pipe are presented. Velocity measurements for both phases were obtained using Laser Doppler Velocimetry; signal discrimination was accomplished through application of the Phase/Doppler principle. Measurements were performed in air containing spherical glass beads with a volume-mean diameter of approximately 45 $mu$m and flowing with a mean centerline velocity between 17 and 24 m/s. The glass particles were able to respond to the most energetic turbulent disturbances in the fluid. Fluid turbulence levels were found to be affected at very low particle mass ratios and to increase monotonically with loading. Specifically, the fluid turbulence level was found to be enhanced by approximately 20% at particle mass ratios as low as 1%. At these low levels of loading, the most dramatic increase in the fluid turbulence intensity occurred near the pipe wall. The centerline turbulence intensity for a suspension with a particle mass ratio of 30% was found to be approximately twice that measured in single-phase flows. The measured particle velocity intensities in pipe flow were found to exceed the levels predicted on the basis of theoretical analyses and experimental measurements of the particle velocity characteristics in grid turbulence. An analysis of the motion of a small particle suspended in a gas flowing with a constant mean velocity gradient predicts that the particle streamwise velocity fluctuations are enhanced by the presence of mean fluid velocity gradients; these enhanced particle velocity fluctuations are expected to lead to creation of additional turbulent kinetic energy. Both the enhanced particle velocities and the enhanced fluid turbulence levels measured near the wall at low particle mass ratios are explained in terms of the existence of mean fluid velocity gradients which exist in this region.