The overall goal of this feasibility study is to produce sub-50 um droplets when spraying highly viscous (up to 100,000 cP) non-Newtonian fluids at process level throughputs (up to 1 kg/s). Work was conducted using a new type of nozzle, developed during the last three years at Purdue, because it is the only candidate likely to meet the sub-50 um criterion.
Work was carried out using fluids comprised of glycerin/water/polymer and coal-water slurry/glycerine/polymer mixtures. Fluids with consistency indices ns high as 41.500 and flow behavior indices as low as 0.27 were employed. All spray data is reported as mean particle size, in terms of the Sauter mean diameter. Mean drop sizes as low as 28 pm have been achieved with air-liquid ratio values of less than 0.20.
The goal of this feasibility study was achieved. In fact, mean drop sizes as low as 38 um were measured at an air-liquid mass ratio of 0.2 and a nominal throughput of 1 kg/s by using an effervescent atomizer, In addition, nozzle performance was shown to improve with throughput, in contrast to the behavior of conventional twin-fluid injectors. Finally, the addition of polymer to either single- or multiphase fluids was shown to increase mean drop size, although the extent of the increase left SMD below the target value of SO um. An explanation for this increase is being pursued.
Work during the next contract year will be focused in three areas: An investigation into how the tightness of the particle size distribution varies with fluid properties and throughput, an investigation into why polymer addition increases mean drop size, and extension of the mathematical model for effervescent atomization developed by the principal investigator and his colleagues to fluids and conditions of interest to IFPRI members. The model will then be used to determine the minimum mean drop size achievable with an effervescent nozzle, given a particular fluid, throughput rind nozzle geometry, and to identify the physical mechanisms responsible for performance barriers associated with effervescent atomizer operation.