| Valve-less piezoelectric pump is a kind of small and micro fluid pump with piezoelectric ceramic as power source part. And this type of pump has some advantages, such as low energy consumption, good controllability of flow, no noise and electromagnetic interference, fast response speed, easy integration manufacturing, and good controllability of micro flow outputting. With integration of traditional pump driving part, transmission part and pump body together, Valve-less pump enhances the system energy conversion efficiency and reduces the wear of moving components. Hence it has wide application prospect in the fields of aerospace, robotics, automotive, medical equipment, genetic engineering, chemical fuel supply, technical scheme of electronic devices and micro machinery in water. But now the research of no-moving part valve in valve-less piezoelectric pump is focused on tube shaped valve and chamber bottom shaped valves, which leads to the complicated structure and machining process of tube or chamber bottom. At the same time, the “valve” with fixed position relative to inlet and outlet will make bad adjustability and controllability of pump flow.Supported by the National Natural Science Foundation of China, this paper carried out the exploratory study on valve-less piezoelectric pump based on the current research. The main research contents are as follows:1. Based on the principle that the flow resistances on spherical surface and round surface of hemisphere-segment are unequal, a valve-less piezoelectric pump with hemisphere-segment as no-moving part valve is presented and designed. Force analysis of hemisphere-segment in pump chamber is carried out by volume and momentum comparison method which is originally innovated. Essential reason that pump can generate one-way flowing is revealed according to fluid mechanics. And pump flow formulas are deduced. A prototype of pump is fabricated andits performance is tested. With the test conditions that ceramic chip diameter 30 mm, uniform distribution of 6 hemispheres in pump chamber, water as working medium, Pumping flow is 0.50 m L/s by driving voltage 110 V and driving frequency 6 Hz; pressure difference reaches to 26.2mm water column by driving voltage 160 V and driving frequency 6 Hz.2. Based on the problem that traditional resistance coefficient calculation method of flowing around non-spheroid can not simultaneously solve forward and reverse flow resistances around hemisphere-segment, the method of Equivalent Flow Resistance Diameter is proposed. And equivalent sphere diameters respectively corresponding to spherical surface and round surface of hemisphere-segment are separated and calculated. The device of testing flow resistance is designed. Resistance coefficient formulas of forward and reverse flow around single hemisphere-segment are deduced. Theoretical Pumping flow rates are calculated and are verified by experiments. The results show that theoretical and experimental pumping flow rate vary in a consistent trend, and the minimum deviation of them is 24.75%, the maximum deviation of them is 31.15%. 3. Formulas of cover flow coefficients, interference coefficients and flow resistance coefficients are established for flowing around two hemisphere-segments arranged in transverse and longitudinal. Then flow resistance coefficient formulas are deduced for any number of hemisphere-segments arranged in transverse and longitudinal, and are verified by experiments. The experimental results show that in definite interval range the pumping flow increases along with the increasing of hemisphere-segment number arranged in transverse and longitudinal. 4. Under the conditions that flow-facing angle is zero and non zero flow resistance coefficient formulas are deduced, and are verified by experiments respectively. The pumping performances are tested with hemisphere-segments arranged in different number of rows, columns, different interval of rows, columns, and different flow-facing angles. The pumping flow respectively is 41.35 m L/min, 46.2m L/min, 45.5m L/min and 47.75 m L/min with hemisphere-segments arranged in 1×1、4×3、3×4、4×4 by driving voltage 120 V, driving frequency 6Hz and flow-facing angle 0°. By the same driving parameters, and lift angle 110 °, with flow-facing angle θy increasing from 0 ° to 45 °, the lift value increases to 78.1mm. During θy continually increasing to 60° the lift value is less than that at θy=45 °, and greater than that at θy=0 °. When θy increases to 90° pump lift value tends to 0. the research in this paper shows: the flow resistance action laws of hemisphere-segment group can be used to analyze and predict pump flow; the pumping performance can be enhanced by increasing the number of rows, columns or appropriately increasing the interval of columns, and decreasing the interval of rows, moreover the pumping performance can be better by increasing the number of rows than by increasing the number of columns; when flow-facing angle θy≤45° the pump flow increases along with the increasing of flow-facing angleθy, and when θy ≈45° the optimal pumping performance can be obtained for the first time.This work is supported by National Natural Science Foundation of China(Grant No. 51075201, No. 51205193), major research plan of National Natural Science Foundation of China(Grant No. 91223201), and Academician Workstation(Grant No. BM2011033). |
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