Study on the Formation and Separation Process of Droplets in the Medical Piezoelectric Atomization Device Induced by Intra‑hole Fluctuation

Traditional atomization devices always exhibit many drawbacks,such as non-uniform atomization particle sizes,instability of transient atomization quantity and uncontrollability of precise energy,which seriously restrict further practical application of atomization inhalation therapy.The formation and separation process of droplets belongs to a microphenomenon of atomization.The investigation of the droplet formation and separation process will be favorable for understanding the atomization mechanism.In present work,the Conservative Level Set Method(CLSM)is successfully applied on the simulation of the formation and separation of droplets in a medical piezoelectric atomization device induced by intra-hole fluctuation.The intra-hole fluctuation mechanism is systematically explored and analyzed,and also the expression of the volume change in the micro cone hole is built and evaluated.Both the control equation and simulation model of droplet formation and separation process have been well established by meshing the simulation model,and thereby the process of droplet formation and separation is simulated.The corresponding results demonstrate that the breaking time of droplets is decreased with the inlet velocity and liquid temperature rising,while enhanced with the liquid concentration increasing.Meanwhile,the volume of droplet is decreased with the inlet velocity and liquid concentration increasing,but increased with the liquid temperature rising.The velocity of droplet is enhanced with the inlet velocity and liquid temperature rising,and reduced with the increase of liquid concentration.When the large side diameter of micro-cone hole is set as 79μm,the breaking time of the droplet reaches a minimum value of 38.7μs,whereas the volume and the velocity of droplet reach a maximum value of 79.8 pL and 4.46 m/s,respectively.This study provides theoretical guidance for the design of medical piezoelectric atomization devices and contributes to the promotion of inhalation therapy in practical use.

Theoretical Calculations and Experimental Verification for the Pumping Effect Caused by the Dynamic Micro-tapered Angle

The atomizer with micro cone apertures has advantages of ultra-fine atomized droplets, low power consumption and low temperature rise. The current research of this kind of atomizer mainly focuses on the performance and its application while there is less research of the principle of the atomization. Under the analysis of the dispenser and its micro-tapered aperture＇s deformation, the volume changes during the deformation and vibration of the micro-tapered aperture on the dispenser are calculated by coordinate transformation. Based on the characters of the flow resistance in a cone aperture, it is found that the dynamic cone angle results from periodical changes of the volume of the micro-tapered aperture of the atomizer and this change drives one-way flows. Besides, an experimental atomization platform is established to measure the atomization rates with different resonance frequencies of the cone aperture atomizer. The atomization performances of cone aperture and straight aperture atomizers are also measured. The experimental results show the existence of the pumping effect of the dynamic tapered angle. This effect is usually observed in industries that require low dispersion and micro- and nanoscale grain sizes, such as during production of high-pressure nozzles and inhalation therapy. Strategies to minimize the pumping effect of the dynamic cone angle or improve future designs are important concerns. This research proposes that dynamic micro-tapered angle is an important cause of atomization of the atomizer with micro cone apertures.