DROPLET DISPERSION AND EJECTION PROCESSES IN 2-PHASE BOUNDARY-LAYER

Measurements of the droplet transport property in the two-phase turbul ent boundary layer were performed in a vertical downward duct by a pha se Doppler particle analyzer (PDPA). The test Reynolds number based on the hydraulic diameter (i.e., D-h = 100 mm) is 70,100 and the drop si ze range is from 3.1 mu m to 110 mu m. Results reveal that the existen ce of drops in the boundary layer has significant effects on both the velocity profile and the turbulence intensities of the flow. Measureme nts show that flow characteristics are controlled by the droplet trans port process, i.e., the dispersion of droplets from the freestream to the boundary-layer region and the ejection of droplets from the bounda ry-layer region to the freestream. Analysis of the data indicates that the normalized number density profiles in the boundary-layer region a re linear and collapse for all drop size classes. The linear coefficie nt of the normalized number density is 1.17 +/- 0.15. The data for the dispersion coefficients are also provided in this paper. The slopes o f the dispersion coefficients for the larger drops (i.e., 50 and 80 mu m) and for the smaller drops (i.e., 20 mu m) are 22.66 and 15.75, res pectively. These data are very useful-in the numeric simulation of the spray flow. Analysis on the experiments data also shows that the drop let ejection factor is 10 and 6% for 20- and 30-mu m drops, respective ly. This implies that modeling of the two-phase boundary-layer problem should consider the droplet ejection process in the small size range.