Abstract
Measurement of liquid film thickness is essential for understanding the dynamics of two-phase flow in microchannels. In this work, a miniaturized sensor matrix with impedance measurement and MEMS technology to measure the thin liquid film underneath a bubble in the air–water flow in a horizontal microchannel has been developed. This miniaturized sensor matrix consists of 5 × 5 sensors where each sensor is comprised of a transmitter and a receiver electrode concentrically. The dimension and performance of the sensor electrodes were optimized with simulation results. The maximum diameter of the sensor ring is 310 µm, allowing a measurable range of liquid film thickness up to 83 µm. These sensors were distributed on the surface of a wafer with photolithography technology, covering a total length of 8 mm and a width of 2 mm. A spatial resolution of 0.5 × 2.0 mm2 and a temporal resolution of 5 kHz were achieved for this sensor matrix with a measurement accuracy of 0.5 µm. A series of microchannels with different heights were used in the calibration in order to achieve the signal-to-thickness characteristics of each sensor. This delicate sensor matrix can provide detailed information on the variation of film thickness underneath gas–water slug directly, accurately and dynamically.
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Abbreviations
- \(D_{\text{Ri}}\) :
-
Inner diameter of receiver
- \(D_{\text{Ro}}\) :
-
Outer diameter of receiver
- \(D_{T}\) :
-
Diameter of transmitter
- \({\mathbf{E}}\) :
-
Electric field
- \(f\) :
-
Frequency
- \(H\) :
-
Height of simulation area
- \(I\) :
-
Current
- \(I^{*}\) :
-
Normalized current
- \({\mathbf{J}}\) :
-
Electric current density
- \(L\) :
-
Length of simulation area
- \(\hat{n}\) :
-
Unit normal vector
- \(R_{t}\) :
-
The maximum roughness height
- \(t\) :
-
Time
- \(t_{ 0}\) :
-
Initial time
- \(V\) :
-
Electric potential, voltage
- \(V^{*}\) :
-
Normalized voltage
- \(W\) :
-
Width of simulation area
- Ca :
-
Capillary number
- \(\sigma\) :
-
Electrical conductivity of media
- \(\varepsilon\) :
-
Material permittivity
- \(\delta\) :
-
Liquid film thickness
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Acknowledgements
This study was performed when one of the authors (Haojie Huang) stayed at University of California, Los Angeles, as a visiting graduate researcher. He would like to acknowledge the support of Natural Science Foundation of China (Grant No: 51376201) and the Chinese Scholar Council. He wishes to thank Prof. Vijay K. Dhir and Liang-ming Pan for their supervisor.
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Huang, H., Dhir, V.K. & Pan, Lm. Liquid film thickness measurement underneath a gas slug with miniaturized sensor matrix in a microchannel. Microfluid Nanofluid 21, 159 (2017). https://doi.org/10.1007/s10404-017-1998-0
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DOI: https://doi.org/10.1007/s10404-017-1998-0