2020 Fiscal Year Annual Research Report
Analysis and control of bubble generation in solid state nanopores
| Project/Area Number |
20J22422
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| Research Institution | The University of Tokyo |
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Principal Investigator |
PAUL SOUMYADEEP 東京大学, 工学系研究科, 特別研究員(DC1)
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| Project Period (FY) |
2020-04-24 – 2023-03-31
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| Keywords | Joule heating / nanopore / bubble nucleation / microelectronic cooling |
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| Outline of Annual Research Achievements |
Control over nanobubble size and generation periodicity is key to realizing a bubble seed emitter for micro-electronic cooling applications. In the past year, the effects of changing nanopore diameter and bias voltages were studied on bubble size and periodicity. Bubble nucleation is actuated inside a solid state nanopore through localized Joule heating. As a bubble nucleates and grows at this hotspot to block the pore, we record transient current dips using a high bandwidth oscilloscope. A signal processing software was developed to analyze the bubble blockage events. Additionally, three theoretical models were constructed: (i) a continuum Joule heating model for nanopore temperature estimation, (ii) a 1D moving boundary model to capture bubble growth and collapse and (iii) a cluster competition model to explain the transition between nucleation modes. Our analysis indicates that as the pore diameter is increased, periodic and homogenous nucleation at the pore center transitions into predominantly heterogeneous nucleation on the pore walls, making the bubble generation stochastic. Also, with an increase in pore diameter, larger homogenous bubbles were generated. These results were summarized into two journal publications (Paul et al., Phys. Rev. Res. 2, 043400 (2020) and Paul et al., JTST 16, JTST0007 (2021)) and presented at two online conferences (57th NHTS (2020) and 73rd APS DFD meeting (2020)).
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
Our target for the first year was to understand the influence of pore diameter on periodic and non-periodic bubble generation in nanopores. Our investigation led us to the finding that transition between homogeneous and heterogeneous nucleation is responsible for the different bubble generation modes observed. This finding and the underlying analyses were well received by the thermal engineering and applied physics community, according to the response from conference audience and journal reviewers. Thus we reach the assessment of "above-expectation progress".
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| Strategy for Future Research Activity |
In the following year, we plan to perform acoustic measurements of bubble dynamics using piezo-electric type hydrophones. In addition, we are working on
developing an optical thermometry experimental setup to measure superheat temperatures inside nanopore, caused as a result of Joule heating. Also, to better analyze the bubble signal data, we are working on adding a machine learning based binary classifier to our signal processing software for clear differentiation between homogeneous and heterogeneous bubbles.
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