| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 95 === This paper investigates the characteristics of a piezoelectric micro-nozzle for the production of mono-size droplet and spray. The micro-nozzle was fabricated by MEMS processes. It consists of the upper and lower chips with dimensions of 20mm×10mm×250�慆. The upper chip is the silicon chip with two holes having diameter of 400�慆, one for the liquid supply, the other for liquid outlet in order to control the injection through the nozzle. A piezoelectric chip with size 12mm×4mm×0.7mm was attached on the upper silicon chip to drive the liquid injection through the nozzle. The lower chip has two designs. One is the silicon chip with a nozzle orifice of 50�慆 in diameter. Another is the glass chip with a nozzle orifice of 80�慆 in diameter. Different working media were employed to characterize the micro-nozzles. Finite element analysis was used to analyze the characteristics of the silicon chip and to control the liquid supply. Liquids were supplied in three ways. The first one was supplied by the elevation head of the working media. The second one was supplied by the pushing mode of the syringe pump at the inlet port. The third one was supplied with the combination of elevation head and the pulling mode of the syringe pump at the outlet port. Results showed that no spray injection took place with liquid supply by elevation head even driven by PZT. However, with liquid supply by the pushing mode of the syringe pump, a single stream of mono-sized droplets was injected through the micro-nozzle with 80�慆 orifice under the driving frequency ranging from 4272 Hz to 5695Hz of PZT. It turned out that the diameter of the droplets was from 206�慆 to 183�慆 under different driving frequencies. Furthermore, with the liquid supply by elevation head as well as the pulling mode of the syringe pump, mono-size droplets with diameter of 16�慆 were injected in turns of DOD basis as the PZT was driven by the resonant frequency, 242 kHz, of the micro-nozzle. It should be noted that the micro-nozzle produces a spray as the PZT was driven by the frequencies other than the resonant frequency of the micro-nozzle. Tests were also performed with the working media as the mixture of water and glycerol of 10wt%, 20wt%, 30wt% and 40wt%. With the liquid supply by elevation head as well as the pulling mode of the syringe pump, atomization took place as the PZT was driven at the frequency of 236 kHz under a voltage of 150Vpp. The result shows in a single stream of droplets with droplet size of range from 13�慆 to 18�慆 of the working medium of water for 30℃. It is concluded that this micro-nozzle can be used in the application of printing service with high speed and high resolution.
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