Transient flow patterns and bubble slug lengths in parallel microchannels with oxygen gas bubbles produced by catalytic chemical reactions |
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| Affiliation: | 1. Department of Mechanical Engineering, Ming Chi University of Technology, New Taipei City, Taiwan;2. Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan;3. Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan;4. Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu, Taiwan;5. Low Carbon Energy Research Center, National Tsing Hua University, Hsinchu, Taiwan;1. Key Laboratory of Enhanced Heat Transfer and Energy Conservation of the Ministry of Education, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China;2. Industrial Energy Conservation Center of Shandong Academy of Sciences, Jinan 250013, Shandong, China;1. Department of Chemical and Biological Engineering, Koç University, Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey;2. Koç University TÜPRAŞ Energy Center (KUTEM), Koç University, Rumelifeneri Yolu, Sariyer 34450, Istanbul, Turkey;1. Institute of Chemical Process Fundamentals v. v. i., The Czech Academy of Sciences, Rozvojova 135/2, 160 00 Prague, Czechia;2. Institute of Environmental Studies, Faculty of Natural Science, Charles University, Benatska 2, 120 00 Prague, Czechia |
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| Abstract: | Transient flow patterns and bubble slug lengths were investigated with oxygen gas (O2) bubbles produced by catalytic chemical reactions using a high speed camera bonded with a microscope. The microreactor consists of an inlet liquid plenum, nine parallel rectangular microchannels followed by a micronozzle, using the MEMS fabrication technique. The etched surface was deposited by the thin platinum film, which is acted as the catalyst. Experiments were performed with the inlet mass concentration of the hydrogen peroxide from 50% to 90% and the pressure drop across the silicon chip from 2.5 to 20.0 kPa. The silicon chip is directly exposed in the environment thus the heat released via the catalytic chemical reactions is dissipated into the environment and the experiment was performed at the room temperature level. It is found that the two-phase flow with the catalytic chemical reactions display the cyclic behavior. A full cycle consists of a short fresh liquid refilling stage, a liquid decomposition stage followed by the bubble slug flow stage. At the beginning of the bubble slug flow stage, the liquid slug number reaches maximum, while at the end of the bubble slug flow stage the liquid slugs are quickly flushed out of the microchannels. Two or three large bubbles are observed in the inlet liquid plenum, affecting the two-phase distributions in microchannels. The bubble slug lengths, cycle periods as well as the mass flow rates are analyzed with different mass concentrations of hydrogen peroxide and pressure drops. The bubble slug length is helpful for the selection of the future microreactor length ensuring the complete hydrogen peroxide decomposition. Future studies on the temperature effect on the transient two-phase flow with chemical reactions are recommended. |
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