In recent years, so-called microfluidics, studies of flow in a microchannel, have been widely developed. Microchannels typically have a channel width that is less than 500 micrometer. Many applications have been considered such as the micro-total analysis systems (micro-TAS) or lab-on-a-chip, DNA and biomedical analyses, and micro-reactors. To consider development of micro-, nano- and picosatellites, utilization of microfluidics will be important. Two-phase flow systems to manage thermal conditions and micro-thrusters for attitude control of satellites are considered for space applications of microfluidics. Although micro-thruster devices have been developed, two-phase flow utilization is not fully understand. Ultrasound was applied to a micropipette micromixer to improve dispersion of gas and liquid in a microchannel. Flow visualization using a high-speed camera was performed to examine the effect of ultrasonic irradiation on bubble generation in the microchannel. Basically, nitrogen gas was injected using a (0.5 micrometer ID) glass micropipette into ethanol flowing in a rectangular (100 micrometer x 200 micrometer) microchannel on polydimethylsiloxane (PDMS). Gas and liquid flow rates were regulated using mass flow controllers. At a flow condition that is typical of bubbly flow, ultrasound was transmitted into the microchannel using a piezo-electric (PZT) transducer over a range of operating voltages (2 to 200 Vp-p) and frequencies (50 to 60 kHz). Images captured during the action of the PZT transducer indicate that bubble formation is influenced by ultrasound. When subjected to ultrasound above 50 Vp-p and at the resonant frequency of the PZT transducer, bubbles formed that were smaller and closer together, signifying enhanced shearing of the gas at the micropipette tip by the liquid. The observation of gas slugs occurring sooner might be attributed to the coalescence of gas bubbles that became closely spaced.
Generation of gas bubbles in microflow using micropipette with ultrasound
Erzeugung von Gasblasen in einer Mikroströmung mit Hilfe von Ultraschall-Mikropipetten
International Topical Team Workshop on Two-Phase Systems for Ground and Space Applications, 2 ; 35-37
Microgravity Science and Technology ; 19 , 3/4
2007
3 Seiten, 5 Bilder, 6 Quellen
Aufsatz (Konferenz)
Englisch
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