| Microbubbles,which refer to tiny bubbles with a diameter of microns dispersed in a liquid medium,are often used in microfluidic drug transport,ultrasonic contrast agents and biochemical precise reactions due to their high specific surface area.For example,in the field of drug transport,the surface of microbubbles can adsorb tiny granular drugs to reach the lesion through blood vessels and achieve the purpose of targeted drug release and treatment through ultrasound force.As the main way to generate microbubbles,two-phase flow technology has problems such as poor adjustment accuracy of microbubble scale and difficulty in real-time regulation.Based on the above content,this paper proposes an electromagnetically driven micro-air pressure generation method,and introduces the ultrasound-induced two-phase flow microbubble forming process to generate monodisperse microbubbles with controllable size.(1)Firstly,the formation mechanism of two-phase flow microbubbles based on ultrasound induction was studied.A method for generating micro-air pressure based on electromagnetic drive was proposed,and the influencing factors of micro-pressure generation were analyzed in depth.According to the fluid-structure interaction effect,a mathematical model was established,and the flow rate of microgas pressure was calculated to be related to the volume change and change rate of compressible space,which laid a foundation for the realization of gas micro-transport.The two-phase flow microbubble generation process was proposed to introduce ultrasonic induction,and the mechanism of T channel microbubble generation was studied and simulated.Further,combined with the derivation of acoustic radiation force,this paper provided a theoretical basis for ultrasoundinduced monodisperse microbubbles with controllable size.(2)Secondly,the structure of micro-gas pump based on electromagnetic drive was designed and further experimental research was carried out.A multilayer structure micropump with PDMS film as the pneumatic driving element was designed and manufactured,and the influence of diaphragm material,PDMS film thickness,excitation frequency and other parameters on the flow and pressure of the micropump was studied.The experimental results showed that when the rated voltage of the electromagnet was 12 V,the diaphragm material was rubber with good elasticity,the PDMS thickness was 100 microns,the driving voltage was 9V,the excitation frequency was 30 Hz,and the distance between the electromagnet and the micropump was 2mm,the pressure of the micropump was 6500 Pa and flow rate is 6.3ml/min.The pump had a higher flow rate resolution than prior technique.(3)Finally,the experiment of generating microbubbles based on ultrasound-induced two-phase flow was studied.Based on the method of generating microbubbles from two-phase flow in the T channel,an experimental device for generating microbubbles from two-phase flow was built.Compared with the gas phase drive method,the gas phase was driven by a micropump for fixed volume and constant pressure,while the liquid phase was driven by a microinjection pump.Observing the experimental phenomenon,it was known that the microbubbles generated under the constant pressure driving gas phase mode are relatively stable.On this basis,an experiment was carried out to generate monodisperse microbubbles with controllable size based on ultrasound-induced two-phase flow.Different ultrasounds were applied to the junction of the two-phase flow,and the changes of microbubble size before and after ultrasound induction were observed by high-speed cameras.The experimental results showed that when the gas phase pressure was 3.8k Pa and the liquid phase flow rate was 1.3ml/min,bubbles with a length of about 2mm were generated in the T channel.When the ultrasonic amplitude is gradually increased under the ultrasound induction generated by PZT5,the length of the microbubble was reduced from the original 2mm to about 0.5mm. |
