The fine particles or aerosols generated using PZT-based technology may be contaminated and are thus not suitable for daily life applications. This potential danger poses serious environmental problems. Additionally, Pb-containing products contaminate soils, plants and even water if disposed without careful precautions. A major drawback of this well-established technology is that lead, Pb is a harmful material that can potentially damage the nervous system and cause brain disorders, particularly in young children 9, 10.
Currently, aside from jet nozzles, the commercially available portable atomizers are based on the use of lead-zirconium-titanate (PZT Pb(Ti, Zr)O 3 polycrystal) as the high-frequency piezo-actuator to generate small droplets 6, 7, 8. Secondary atomization represents the subsequent breakdown of droplets due to the shearing effect of air flow 2, 3, 4, 5.Ītomizers are currently used in diverse applications, including agriculture (e.g., pesticide sprayers), industry (e.g., surface treatment), and medicine (e.g., humidifiers and nebulizers), and the atomizers used are mainly based on ultrasonic, piezoelectric and jetting mechanisms. A stable droplet is formed when the surface tension is strong enough to maintain the spheroidal shape of the drop ejected from the nozzle. A lower viscosity leads to a larger velocity of fluid being propelled forward, which results in a longer tail of the droplet. At this stage, the primary stresses that transform the liquid sheet into droplets are surface tension, viscosity and inertial stress. Primary atomization occurs near the orifices where the liquid sheet is subjected to interact with air flow. There are two main types of atomization: primary atomization and secondary atomization. It is envisioned that the successful development of this MEMS-based atomizing technology will revolutionize the existing market for atomizers and could also benefit different industries, particularly in applications involving viscous fluids.Ītomization, also defined as the disintegration of liquid, is a process of turning a liquid into droplets or vapor in which the ratio of surface to mass is increased 1. In addition, different modes of spraying are reported for the first time.
The particle image velocimetry (PIV) results indicate that the diameter of the ejected droplets ranges from 30 to 90 μm with a speed of 20 to 340 mm/s. The relationships between the micro-heater track width and the track gap, the size of the micro-cavities and the nucleation energy were studied to obtain an optimal atomizer design. The results demonstrate that the average power consumption of the atomizer is approximately 1 W with an atomization rate of 0.1 to 0.3 mg of deionized (DI) water per cycle. It has been tested to be applicable over a wide range of fluid viscosities, ranging from 1 cP (e.g., water) to 200 cP (e.g., oil-like fluid) at room temperature, a range that is difficult to achieve using ordinary atomizers. It is a low-cost, lead-free design that is environmentally friendly and harmless to humans. The development of a novel lead-free microelectromechanical-system (MEMS)-based atomizer using the principle of thermal bubble actuation is presented.