The Principle And Cooling Application Of The Atomizer With Vibrating Micro Tapered Apertures

Atomization is a process that liquid is injected into the gas medium to be dispersed and fragmented into small droplet.Atomization is widely used in our daily life,industrial,agricultural and medical applications.Different with traditional atomizer,the atomizer with vibrating micro tapered apertures uses piezoelectric ceramics as its drive source.It has attracted great attention for its simple structure,high atomizing efficiency,high-viscosity liquid atomization,small and evenly distributed atomized droplets.Existing literatures mainly focus on the performance and application research of the atomizer with vibrating micro tapered apertures,while its atomization theory is short of research.Based on the analysis of liquid flowing in the micro-cone,the working principle of the atomizer is found.Then,the formation of atomized droplets is analyzed and the atomizer’s applications of spray cooling is discussed.Research work provides a theoretical basis of the optimization and improvement of the atomizer with vibrating micro tapered apertures.Specific contents are as follows:1.The theory of the pumping effect generated by the atomizer with vibrating micro tapered apertures was discovered.First,the variation law of the volume of micro tapered apertures was calculated using the coordinate transformation method.Then,based on the characters of the flow resistance in a tapered aperture,it is found that the dynamic cone angle results from periodical changes of the volume of the micro-tapered aperture on the dispenser and this change drives one-way flows.An experimental atomization platform was established to measure the atomization rates of cone aperture and straight aperture atomizer and the atomization rates when the atomizer is under different resonance frequencies are also measured.The experiments show that the atomization rates in the forward flow are much larger which in the reverse flow when there are tapered apertures in the dispenser,while the atomization rates of straight apertures were independent with their directions;and the atomization rate increases with the complexity of the dispenser’s deformation.The experimental results show the existence of the pumping effect of the dynamic cone angle.2.The liquid flow characteristics in the micro tapered aperture were calculated.Analytical and computational fluid dynamics methods are adopted to calculate the influences such as Reynolds number,cone angle,slenderness and area ratio on the loss coefficient.The calculation results show that the loss coefficient of nozzle is only affected by the cone angle and it decreases with cone angle,while the loss coefficient of diffuser is mainly effected by the cone angle and slenderness and area ratio also have impacts on the loss coefficients.Furthermore,the dynamic cone angle effect can be enhanced by increasing the cone angle.Research results provide a theoretical basis of the optimization design of the atomizer.3.The formation process of atomized droplets was calculated.The linear instability theory and capillary waves breaking theory were studied,the calculation results based on these two theories were compared with existing literature data.It is found that both these two theories are not suited for the atomizer with vibrating micro tapered apertures.The formation of atomized droplets was calculated by the boundary element method,and it is found that the atomized droplets are formed mainly due to periodic negative pressure in the micro tapered apertures drags ejected liquid.The influence factors on droplets formation such as cone angle,the amplitude and frequency of the pressure in aperture are calculated.The results provide theoretical basis of the droplet control of the atomizer.4.Spray cooling characteristics of the atomizer with vibrating micro tapered apertures were studied by experiments.The spray cooling is widely used due to its large convective heat transfer coefficient and steady temperature control.The spray cooling system was set up using rotating heating pipe as heating source,the impacts of parameters,such as atomization rate,atomization height,driving frequency and heating pipe rotate speed,on spray cooling performance was studied.The results show that the maximum cooling capacity of the atomizer is 60.13 W when atomization rate is 2.56 ml/min.Atomization rate and atomization height have significant influence on spray cooling performance,while driving frequency and heating pipe rotation have little influence.The effect of atomization height is also related to atomization rate.