| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 93 === In this study, we develop our whole objective lens-based laser Doppler anemometry by introducing the ultra long working distance objective lens instead of using conventional lens to focus beams and generate the measuring volume. This schemes to reduce the interference spacing and meantime to maintain sufficient pattern number. In addition, thus-designed instrument also provides adequate operation space for measuring flow field in micro-fluidic devices.
After calibrating our LDA system, we can discover that probe volume has spacing less than 1μm, and that over 10 pattern numbers has in it. This system can minimize its spacing by easily introducing higher multiplication objective lens and thus improving its spatial resolution. Simultaneously, the new acoustic modulation device and data processing program enable this whole objective lens based LDA to discriminate reversed flow field. Besides, we also set up two kinds of light path mode: reference and dual beam mode. While testing and comparing both mode’s signal quality, we reconfirm that the dual beam mode has less noise in sensing signal.
In this experiment, we generate an electro-spray and apply a micro channel flow as our testing bed. By establishing suitable light path mode for LDA, this system can find out the velocity profile of electro-spray, and it also obtains a linear changed speed condition in micro channel when fluid was driven by a syringe pump under several pumping rate, even in an over-seeded situation. Meanwhile, by observing the capillarity wetting of electro-spry which cause the sweeping of spray, we realize that it is necessary to control both surface tension and electric field at the same time to stabilize the spray direction if we apply larger flow rate to spray than usually used. Finally, the micro channel flow measuring results tells us that the more dense seeding un flow will not accurately respond to the real flow speed in the micro channel.
In the future work, we prepare to use this tool with self-made seeding to investigate the pulse flow field in the electro-hydro dynamic pumping driven chip, or to measure velocity of particles and then estimate the particle properties in dielectrophoretic-force driven chip.
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