Droplet dispersion and ejection processes in two-phase boundary layer

Abstract

Measurements of the droplet transport property in the two-phase turbulent boundary layer were performed in a vertical downward duct by a phase Doppler particle analyzer (PDPA). The test Reynolds number based on the hydraulic diameter (i.e., D(sub h) = 100 mm) is 70,100 and the drop size range is from 3.1 micron to 110 micron. Results reveal that the existence of drops in the boundary layer has significant effects on both the velocity profile and the turbulence intensities of the flow. Measurements show that flow characteristics are controlled by the droplet transport process, i.e., the dispersion of droplets from the freestream to the boundary-layer region and the ejection of droplets from the boundary-layer region to the freestream. Analysis of the data indicates that the normalized number density profiles in the boundary-layer region are linear and collapse for all drop size classes. The linear coefficient of the normalized number density is 1.17 +/- 0.15. The data for the dispersion coefficients are also provided in this paper. The slopes of the dispersion coefficients for the larger drops (i.e., 50 and 80 micron) and for the smaller drops (i.e., 20 micron) are 22.66 and 15.75, respectively. These data are very useful in themore » numerical simulation of the spray flow. Analysis on the experiments data also shows that the droplet ejection factor is 10 and 6% for 20 and 30 micron drops, respectively. This implies that modeling of the two-phase boundary-layer problem should consider the droplet ejection process in the small size range. 18 refs.« less