Mechanization, Method And Effect Of The Liquid Piezoelectric Pump Bubble Controlling

Liquid piezoelectric pump has the advantages of small volume, high cost performance ratio and high precision of flow control, which makes it have good application prospects in the fields of biomedicine, fine chemical industry, civilian consumption and portable micro electromechanical testing equipment. But the stability of the existing piezoelectric pump is not as good as expected, because of the extreme sensebility to bubbles. Once there is a bubble, the performances, such as output flow, output pressure, etc., declines sharply and self-suction capability is nearly lost, which constrains the application of piezoelectric pump highly. The bubble formation in piezoelectric pump has a variety of reasons. Besides the bubble which is formed by suctioning fluid from outside, the aggregation, mergence, and growth of the micro air mass in flow channel and pump chamber which is compressed by the vibration of piezoelectric vibrator and the cavitation caused by the pressure change because of the channel sudden change when the liquid flows are the second main source of the bubble. It is almost inevitable, because it happens during the piezoelectric pump works. There are two ways to remove the negative effect of bubbles, restraining the adhesion of the bubbles and eliminating bubbles rapidly.This paper is based on the National Natural Science Foundation project "Mechanism, Method and Effect Research on Wall Wettability Optimization in Piezoelectric Pump Bubble Controlling"(NO.51406065). Under the premise of ensuring the miniaturization of the piezoelectric pump, this paper analyzes the mechanism of the effect of the bubble on the output performance of the piezoelectric pump, and then prove the intrinsic factors of the bubble retention. The relevant dynamic mathematical model is established, the technical and theoretical basis for improving the performance of piezoelectric pump to eliminate bubbles is provided. Overall content as follows:1. Influence mechanism research on the bubble retention for the output performance of piezoelectric pumpThe structure and working principle of piezoelectric pump are described and the influence of bubble retention in the pump chamber and valve to the output performance of piezoelectric pump is analyzed. Firstly, the basic equation of piezoelectric pump is established and the influence of bubble retention in the pump chamber to the output pressure and output flow of piezoelectric pump is analyzed. Meanwhile, a simplified dynamic model of piezoelectric pump is set up when the bubble is detained in the valve, to analyse the influence mechanism of the bubble on the piezoelectric pump. The influence mechanism of capillary force on valve dynamic performance when the valve is surrounded by the bubble is analyzed, based on the established dynamic model. By analyzing the process of dissolving out and dissolution of air in the liquid and the dynamic volume change of bubbles under the influence of alternating stress, the volume equation of cavitation is given, when the pump chamber cavitation occurs.2. Mechanism and effect research on the applying of the valve plate parameter optimization in bubble controllingOne way valve is an important part of the piezoelectric pump, bubbles prone to be detained in the valve plate。Two phase flow pattern exists mainly in the piezoelectric pump when the bubble is involved in the working fluid, and the pressure loss is analyzed when multiple bubble flow and piston flow through the valve in homogeneous flow, which explains the reason of the bubble retention in the valve, and the optimization measures of the valve plate to improving the ability of piezoelectric pump to eliminate bubbles are put forward. The correctness of the conclusion is verified by experiments。At the same time, the different flow field distribution in the chamber of the pump corresponding to four different valve hole arrangements are analyzed through Fluent。The bubble possible retention area and the ability to eliminate bubbles in four different valve hole arrangements are obtained, and the ability to eliminate bubbles is verified by experiments.3. Mechanism and effect research on the applying of compression ratio optimization in bubble controllingThe compression ratio is an important parameter which determines the output performance of piezoelectric pump. In order to achieve the compression ratio optimization, this project changes the cavity height and optimize driving source. The influence of compression ratio on piezoelectric pump output performance is analyzed, the causes that the bubbles are detained in the chamber are analyzed by the plate gap flow model, and the relevant optimization method is devised.The ability of eliminating bubbles is verified by the experiment of different cavity height, and the optimal cavity height is obtained. A lead-flow path is proposed to reduce the retention of bubbles, and experimental research is done on it in this work.4. Mechanism and effect research on the applying of wall wettability optimization in bubble controllingThe influence mechanization of the optimization of wall wettability on eliminating bubbles is analyzed. The transformation relationship of the wall wettability at the alternating pressure and different temperatures is analyzed. The dynamic characteristics of the bubble in the pipe, the wall wettability of which is optimized is analyzed. Through the super hydrophilic / hydrophobic treatment of the pump cavity and the valve plate, the bubble retention experiment is carried out to verify the effect of eliminating bubble of piezoelectric pump after the optimization of wall wettability.This paper discusses the mechanization and controlling of bubble detained in the piezoelectric pump, which has combined the relevant theory of the piezoelectricity, mechanical dynamics, fluid dynamics, hydrodynamics, material science, electricity and interface biomimetic modification technology. The research work provides theory and technology foundations for the micro-piezoelectric pump in the design of bubble controlling, and has good consultant valuation for the similar fluid conveying equipment.