Active Control of Liquid Jet Breakup for Advanced Manufacturing

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Liquid sprays and aerosols play an important role in a myriad of manufacturing environments, from food and chemical processing to netshape manufacturing and pharmaceuticals. For each application, the ideal size of the droplets in the spray and their desired momentum varies. Currently, however, liquid droplets are generated during a vigorous and chaotic breakup event from a bulk fluid, making prediction and control of droplets difficult. Improved real-time control of droplet size and trajectory could therefore have significant impacts on advanced manufacturing and processing methods. This project?s goal is to demonstrate a novel approach for generating, manipulating, and controlling droplets. The concept is to develop a control methodology for adjusting the breakup of a simple capillary jet into droplets with predictable and variable size and momentum. While the mechanism for capillary jet breakup is not identical in all complex sprays, it can serve as a model for the development of control strategies for other droplet and spray applications as well.The breakup of liquid jets into uniform droplets in response to ideal perturbations on the jet has been studied for many years. In practical systems, however, actuator dynamics make it difficult to create a pure excitation, thereby limiting the breakup performance to a small range of droplet sizes. In the proposed work, we explore the possibility of expanding the breakup performance window by controlling the input waveforms to the perturbation source in order to suppress disruptive components. The study begins by identifying the response dynamics of a typical piezoelectric actuator to a pure sinusoidal input. An inverse problem solution then produces the non-sinusoidal input wave needed to suppress undesirable response modes and ensure that the actuator perturbs the jet with only one dominant frequency. Experimental verification of this open-loop control performance on a liquid jet follows. The project then develops a real-time identification approach to allow corrections and adjustments to the input waveform in response to the desired output droplet behavior. Hence, the project has two elements: (1) a control component that uses the dynamic features of the perturbed capillary jet to develop a system model to which control techniques can be applied and (2) an experimental component that develops a capillary jet breakup system and control apparatus that can be stimulated and controlled via sensor and actuator feedback loops in order to verify the control findings.