Study And Experiment On Micromanipulation Mechanism Of Micro-nano Powder Acoustic Streaming

The use of low-frequency ultrasound to manipulate cells or particles usually results in nonlinear or vortex trajectory motion,which seriously affects the control accuracy;In the research of ultrasonic phased array and ultrasonic internal processing,the actual position and motion trajectory of the controlled object and the theoretical existence also appear In addition,in the sound field micro-nano powder control,the micro-powder sprayed by the micro-nozzle under the action of the sound field does not move along the nozzle axis,but vortex-like motion occurs at the nozzle mouth,obviously ultrasonic standing wave acoustic radiation It is difficult to explain this movement phenomenon and fundamentally solve problems such as poor injection accuracy.The vortex motion shows that the second-order acoustic field is derived from the energy loss of viscous and other energy when the ultrasonic wave propagates in the air.The second-order acoustic phenomenon represented by the acoustic current(AS)is used in ultrasonic cleaning,cell mixing,micro-nano control and heat conduction.There are broad application prospects.Based on this,this paper takes the acoustic flow as a breakthrough,proposes to excite the sound field outside the microchannel,deeply analyzes the distribution of the second-order nonlinear sound field and its mechanism of action on the powder,and carries out experimental research,so as to realize the controllable injection of the powder trajectory.Firstly,through theoretical analysis,this paper explores the feasibility of using Acoustic Streaming Field to control micro powder in microchannel.Three hypotheses are put forward:first,the Acoustic Streaming formed outside the nozzle,the nozzle mouth and inside the nozzle will form different forms of Acoustic Streaming.First,the Acoustic Streaming formed outside the micro nozzle will cause the cylinder to deflect,and the vortex induced vibration caused by the deflection flow will drive the micro powder to fall off;Secondly,the acoustic flow formed at the nozzle orifice will form a Bernoulli negative pressure at the nozzle orifice,thereby driving the fallen powder to move toward a certain rule Exit movement;Thirdly,the Acoustic Streaming formed in the microchannel will scour the micro powder and accelerate the micro powder shedding.Secondly,the distribution of Acoustic Streaming field inside and outside the microchannel is studied by numerical simulation,and the simulation analysis of the micro powder controlled injection is carried out.The second-order Acoustic Streaming excited by the first-order sound field,such as the cylinder acoustic torsion flow and sharp edge acoustic streaming,is theoretically deduced and the mathematical model is established Multiphysics finite element software is used to establish the numerical model of sound field and flow field,and numerically simulate the acoustic torsion flow process of a cylinder;the ultrasonic traveling wave field is scanned in frequency domain and space,and the fluid structure interaction between the flow field and the cylinder under different frequencies and spatial positions is explored;The difference of symmetry between reflected standing wave acoustic flow field and superimposed standing wave acoustic flow field is proposed,and the frequency domain and spatial position scanning of reflected standing wave acoustic flow field and superimposed standing wave acoustic flow field are carried out respectively.The simulation results show that the superposition of standing wave acoustic flow field can fundamentally solve the problem of controllable injection of powder trajectory.Finally,the experiments were carried out to control the injection of angular copper powder,tin powder and titanium alloy powder.The experimental results verify the accuracy of theoretical derivation,mathematical model and simulation analysis results.The experimental results show that the traveling wave acoustic field(TWSF)or reflected standing wave acoustic field(RSWF)deflects the micro powder trajectory due to the asymmetric viscous loss,while the superimposed standing wave acoustic field(SSWF)can control the micro powder moving along the micro nozzle axis well,and the deviation error of the micro powder around the micro nozzle axis is less than 1.58)8).The problem of controllable injection of sound field on the trajectory of micropowder is effectively solved.