The long-term objective of this research is to develop an ultrasonically excited spray nozzle that will remove coal, silica and diesel particulates from mining environments. Water sprays are already used in mines to reduce dust levels. However dust levels remain unacceptably high and mine workers suffer from a range of respiratory diseases. Mortality rates due to these conditions are high. The sprays used in mines are ineffective in removing particles in the particle diameter range that is most damaging to the human lung: dp = 0.1um to 1.0 um. The ultimate objective of this research is to develop an ultrasonically excited nozzle that will increase the efficiency of particle scavenging by drops for this range of particle diameters. This project consists of a study into three interrelated facets of how drops scavenge particles: (1) drop oscillations, (2) drop wakes, and (3) ultrasonic oscillations of drops. The specific objectives of this work are to first understand how these three mechanisms separately affect particle scavenging. That is, experiments will be conducted to reveal how drop oscillations, drop wakes and ultrasonic oscillations of drops affect the scavenging of particles, for drops and particles relevant to the mining environment. Once this has been understood, these three mechanisms will be combined to ascertain how they interact and how these interactions affect particle scavenging. The final result of this research will be an understanding of how to design an ultrasonically excited nozzle capable of removing 0.1um to 1.0um diameter particles from mining environments. The objectives of this project will be achieved by a set of laboratory experiments, where the scavenging of particles by water droplets will be measured. This will be done by creating monodisperse distributions of particles comprised of a fluorescent dye. The mass of particles scavenged will be measured by collecting the drop fluid and measuring the amount of dye present using a spectrofluorometer. These measurements will be used to compute the scavenging coefficient, E. Three sets of experiments will be conducted. In the first set, drops will fall through particle laden air, and the effect of naturally occurring oscillations on E will be determined for a range of drop diameters and particle sizes. These experiments will show how relatively small drop oscillations affect scavenging in a high speed flow. In the second set of experiments, drops will be acoustically levitated and subjected to large oscillations through ultrasonic stimulation;however the flow of air over these drops will be low. Again, drop and particle diameter will be varied and their effect on E will be ascertained. In the final set of experiments, drops will be projected at high velocity, past an ultrasonic source to measure scavenging of drops subjected to large oscillations due to ultrasonics, while traveling at high velocity. Several characteristics of the ultrasonic excitation will be varied to maximize particle scavenging.
The proposed research will significantly improve the health of the U.S. mining work force by ultimately reducing the level of respirable particles in mining environments. The knowledge generated in the proposed studies will ultimately be used to design a nozzle that is better able to remove coal, silica and diesel particulates from mining environments. These particles results in many pulmonary ailments and deaths, and their reduction will reduce mortality rates and pulmonary disease within the mining work force.
