Ultra-efficient two-phase evaporators/boilers enabled by nanotip-induced boundary layers
Microfluidic devices, along with methods of their fabrication, are provided. The microfluidic device can include a substrate defining a microchannel formed between a pair of side walls and a bottom surface and a plurality of nanotips positioned within the microchannel and proximate to each side wall such that a boundary layer is formed along each side wall between the plurality of nanotips and the side wall upon addition of a liquid into the microchannel.
1. A microfluidic device, comprising:
a substrate defining a microchannel formed between a pair of vertical side walls and a bottom surface;
a pair of aligned nanotip arrays positioned within the microchannel, each nanotip array extending from the bottom surface of the substrate adjacent a vertical side wall such that a boundary layer is formed along an upper end of the vertical side wall between the nanotip array and the vertical side wall upon addition of a liquid into the microchannel, wherein each nanotip array comprises a plurality of vertically-extending nanotips; and
a midchannel gap extending between the pair of aligned nanotip arrays, the midchannel gap having a length and a width, wherein the midchannel gap is free of nanotips along the length and the width, wherein the width of the midchannel gap is from 170 μm to 495 μm, wherein the microchannel defines a microgap resent between one of the pair of aligned nanotip arrays and a nearest vertical side wall, wherein the microgap has a width ranging from about 2.5 μm to about 15 μm.
2. The microfluidic device as in claim 1 , the microchannel defining a diameter measuring the shortest distance between the side walls, wherein each nanotip defines an average pitch that is at least 20 times smaller than the diameter of the microchannel.
3. The microfluidic device as in claim 1 , wherein each nanotip defines an average pitch that is at least 10 times smaller than the diameter of the microchannel.
4. The microfluidic device as in claim 1 , wherein a pitch between the nanotips is from about 2 μm to about 10 μm.
5. The microfluidic device as in claim 1 , the microchannel defining a diameter measuring the shortest distance between the side walls, wherein the diameter of the microchannel is about 200 μm to about 500 μm.
6. The microfluidic device as in claim 5 , wherein each nanotip defines an average pitch of about 1 μm to about 20 μm.
7. The microfluidic device as in claim 1 , wherein the substrate comprises silicon.
8. The microfluidic device as in claim 7 , wherein a glass wafer is positioned on the substrate to enclose the microchannels.
9. The microfluidic device as in claim 1 , wherein the pair of nanotip arrays are integrally formed from the same material as the substrate.
10. The microfluidic device as in claim 2 , wherein the microgap is greater than 5.0 μm.
11. The microfluidic device as in claim 1 , wherein the nanotips are tapered vertically.
12. The microfluidic device as in claim 1 , wherein each of the nanotips are independent.
13. The microfluidic device as in claim 1 , further comprising a second microchannel in parallel and having a substantially similar internal structure as the microchannel.