Many manufacturing and industrial applications benefit from fluid atomization to create a fine vapor mist or aerosol, such as the fuel/air mixture used in combustion applications, atomized air-paint mixtures for spray painting, application of coatings to pharmaceuticals, adhesive applications, and the like. Once a component solution is made into an aerosol it can be readily processed to coat virtually any shaped surface. Alternatively, in the pharmaceutical industry, aerosols are commonly used in a process called “spray-drying” to create fine powders that serve as upstream component solutions to create active pharmaceutical ingredients.
In all known applications, creating the aerosol from a component solution is challenging. When the component solution behaves like a Newtonian fluid, the creation of a vapor or aerosol is accomplished by a number of conventional methods. One conventional method uses high velocity air flows to entrain air and liquid. A typical atomizer or aerosol involves the coaxial flow of air and component solution at large Reynolds and Weber numbers, i.e., the inertial forces dominate the viscous and surface tension forces in the fluid. Such flows are generally unstable and lead to fluid break-up by Kelvin-Helmholtz and Plateau-Rayleigh instabilities. In many instances, the flow is turbulent and chaotic, which strips and stretches the fluid parcels at high strain and strain rates, which leads to the entrainment of large amounts of air with the fluid and results in a fine mist of drops suspended in the air.
High velocity coaxial flows are effective when the component solution has Newtonian properties and behaves like a Newtonian fluid. However, many component solutions contain a variety of macromolecular and interacting solids components that lead to non-Newtonian properties, including shear-thinning and viscoelasticity. Conventional methods of atomization like high velocity coaxial flows and electrospray can be ineffective for component solutions that have non-Newtonian properties. For example, if a component solution is viscoelastic and strongly extensionally thickening, its extensional viscosity can increase by several orders of magnitude in the straining direction when the fluid is stretched, i.e., greater than 105 for some high molecular weight polymer component solutions.
During jetting, the extensional thickening of component solutions having non-Newtonian properties causes the viscous drag to overwhelm the inertial and surface tension forces, which allows the system to support large strain before breaking-up and preventing the formation of small drops. The jetting leads to the formation of long, sticky filaments, films, and tendrils that never break-up and become suspended in air. Essentially, the liquid stretches, but never breaks into droplets to form a mist or vapor.
The principal problem with coaxial flow systems to create aerosols is that the straining direction is coincident with the translation direction. The filament eventually breaks up into droplets to form a mist, but to achieve the large strain the filaments issuing from the jet must necessarily travel long distances. As the filaments travel, the filaments lose momentum and can recoil to reform large droplets. Alternatively, attempts to continually impel the filament during its trajectory require impractically long jetting to break the filaments and form droplets.
Therefore, methods and systems that create aerosols from fluids that show one or both of Newtonian and non-Newtonian properties would be beneficial in the art.