THESIS
2016
xiv, 101 pages : illustrations ; 30 cm
Abstract
Fluid flows at micro- and nanoscale are essential in integrated fluidic devices and micro total analysis systems such as Micro-/Nano-Electro-Mechanical Systems (MEMS/NEMS), which have tremendous applications in biology, medicine, chemistry and engineering. Nanoscale flows could be very different from macroscopic flows due to the high surface-area-to-volume ratio and complex molecular interactions. To promote the applications of nanoscale flows, extensive work is required to study the flows in nanoconfinements. The objectives of this thesis are to investigate the flow fashions and explore the applications of nanochannel flows through experiments.
First, the Poiseuille flows in nanochannels are examined. Experimental results show that the flow rate undergoes a transition between two...[
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Fluid flows at micro- and nanoscale are essential in integrated fluidic devices and micro total analysis systems such as Micro-/Nano-Electro-Mechanical Systems (MEMS/NEMS), which have tremendous applications in biology, medicine, chemistry and engineering. Nanoscale flows could be very different from macroscopic flows due to the high surface-area-to-volume ratio and complex molecular interactions. To promote the applications of nanoscale flows, extensive work is required to study the flows in nanoconfinements. The objectives of this thesis are to investigate the flow fashions and explore the applications of nanochannel flows through experiments.
First, the Poiseuille flows in nanochannels are examined. Experimental results show that the flow rate undergoes a transition between two linear regimes as the shear rate is varied. The transition indicates that the nonslip boundary condition is valid at low shear rate. When the shear rate is larger than a critical value, slip takes place and the slip length increases linearly with increasing shear rate before approaching a constant value.
Second, a nanofluidic diode for simple fluids without moving part is proposed and investigated by using heterogeneous nanochannels, half of which is hydrophilic and the other half is hydrophobic. The device accepts water flows in the direction from hydrophilic to hydrophobic, while the flows in the other direction are blocked for pressure drop range between 0 and 0.63 MPa. As the upstream pressure becomes higher than 0.63 MPa, the fluidic diode turns to be a rectifier, which allows flows in both directions but with different flow rates. At sufficient high driving pressure, the fluidic system fails in flow rectification, analogous to the breakdown of electro diodes.
Finally, a waste heat driven self-adaptive cooling system based on heterogeneous nanochannels is fabricated and studied. It is found that continuous coolant flux from the hydrophilic side to the hydrophobic side can be generated under symmetric temperature gradients. Linear dependence of volumetric flux on the temperature gradient is observed. The mechanism of flow behaviors is evaluated through the coupling effects of temperature gradient and fluid-surface interaction.
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