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Final Report: Flow Control and Design of Environmentally Benign Spray Systems
EPA Grant Number: R829587Title: Flow Control and Design of Environmentally Benign Spray Systems
Investigators: Plesniak, Michael W. , Frankel, Steven H. , Shu, Fangjun , Sojka, Paul E.
Institution: Purdue University - Main Campus
EPA Project Officer: Richards, April
Project Period: January 1, 2002 through December 31, 2004
Project Amount: $350,000
RFA: Technology for a Sustainable Environment (2001)
Research Category: Pollution Prevention/Sustainable Development
Description:
Objective:The objective of this research project was to reduce air pollutant emissions by improving droplet transfer efficiency (i.e., reducing overspray and hence reducing particulate and solvent effluents in spray coating processes).
Summary/Accomplishments (Outputs/Outcomes):The working hypothesis was that increasing the turbulence intensity near the target surface would enhance the deposition of small paint droplets that would normally be swept away by the flow parallel to the target, resulting in overspray. The method chosen to enhance turbulence is a passive method in which specially-shaped nozzles, that is nozzles of indeterminate origin (IO), are used to promote turbulence. The mechanisms by which IO nozzles influence the jet’s turbulence structure and evolution were investigated and reported in previous annual reports. Quantitative Particle Image Velocimetry measurements were reported for free jet and impinging jets, which model the basic stagnation flow configuration representative of a paint spray impinging upon the surface to be painted. The IO nozzles had maximum influence on jet structure in the near-nozzle region (within several nozzle diameters), but the effects decayed with downstream distance. The IO nozzle influenced the jet structure by introducing streamwise vortex pairs, which interacted with the turbulent structures present in the jet. As the jet propagated downstream, the streamwise vortices weakened and their effect diminished, so it was unclear whether such passive control of the turbulence at the nozzle would persist in sprays to yield beneficial effects on drop transfer efficiency at the target.
This final report focuses on the most recent findings concerning investigation of actual sprays. To examine the influence of IO nozzles in an actual spray, the performance of an effervescent atomizer controlled with IO nozzles was investigated. The results were compared with the traditional round nozzle spray case. The IO nozzles influenced the spreading angle of the spray (and hence entrainment of ambient air), but they did not increase the wall-normal velocity fluctuation in the downstream region; therefore, transfer efficiency was not increased when using IO nozzles. Direct measurements of the transfer efficiency confirmed that overspray was not reduced, at least for the configurations tested with a particular atomizer. Based on the detailed understanding of the complex flow physics gained under this project, improved control methodologies have been formulated.
Conclusions:The following conclusions were drawn from the results of the study: (1) IO nozzles can control the jet characteristics in the near-nozzle region by introducing a complex system of streamwise vortices; (2) streamwise vortices are generated in the valley locations, and after reorganization they move to the peak locations as they propagate downstream; (3) IO nozzles primarily influence the jet turbulence characteristics near the nozzle, but the effects diminish in downstream regions (x/D > 7); (4) IO nozzles can modify the spreading angle and entrainment of a spray but appear not to increase the transfer efficiency (TE); (5) direct measurements of TE confirmed that TE was not increased when using IO nozzles so the proposed method of reducing overspray is not effective because the turbulent fluctuations that are initially controlled at the nozzle relax back to their initial state by the time the spray transits to the target); and (6) IO nozzle flow physics suggest that some form of active control is required to yield persistent beneficial effects of IO nozzles for improving TE (i.e., minimizing overspray).
Journal Articles on this Report: 2 Displayed | Download in RIS Format
| Other project views: | All 14 publications | 2 publications in selected types | All 2 journal articles |
| Type | Citation | ||
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Shu F, Plesniak MW, Sojka PE. Frontispiece: Visualization of streamwise vortex pairs in an indeterminate origin (IO) nozzle jet. Journal of Visualization 2005;8(3):195. |
R829587 (2004) R829587 (Final) |
not available |
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Shu F, Plesniak MW, Sojka PE. Indeterminate-origin nozzles to control jet structure and evolution. Journal of Turbulence 2005;6(26):1-18 |
R829587 (2004) R829587 (Final) |
not available |
engineering, particulates, toxics, VOC, pollution prevention, innovative technology, environmentally conscious manufacturing, surface coating,
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Toxics, Air, Sustainable Industry/Business, Scientific Discipline, RFA, Technology for Sustainable Environment, Sustainable Environment, Chemical Engineering, Civil/Environmental Engineering, air toxics, Environmental Engineering, cleaner production/pollution prevention, Environmental Chemistry, Chemistry and Materials Science, New/Innovative technologies, VOCs, 33/50, Engineering, clean technology, environmentally benign spray systems, ligament-controlled effervescent atomization technology, chromium & chromium compounds, cleaner production, Volatile Organic Compounds (VOCs), waste reduction, coating processes, sustainable development, spray processes, Chromium, waste minimization, environmentally conscious manufacturing, lead & lead compounds, particulates, sustainability, coatings, environmentally friendly technology, phase doppler particle analyzer, flow control, overspray reduction, innovative technology, chemical use efficiency, surface coating, emission controls, green technology, innovative technologies, pollution prevention
Relevant Websites:
http://widget.ecn.purdue.edu/~tfpl/project_flowcontrol.htm
Progress and Final Reports:
2002 Progress Report
2003 Progress Report
2004 Progress Report
Original Abstract