Design and Characterization of an Electrohydrodynamic (EHD) Micropump for Cryogenic Spot Cooling Applications
Ohadi, Michael M.
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High-temperature superconducting (HTSC) components are being incorporated into communication and monitoring electronic devices to increase their signal-to-noise ratio or their channel capacity. Those devices must be maintained at cryogenic temperatures to prevent the loss of their superconducting properties and retain their performance superiority. They are conventionally cooled via direct heat conduction, which leads to undesirable temperature differences among the various components being cooled. Compact micropumps capable of pumping liquid nitrogen at 77 K into liquid-cooling circuits would enable a much more compact and lightweight method of maintaining a uniform temperature across the cooling circuit. These pumps can also address the demand for delivering small doses of LN2 to particular spots in bioengineering applications.<br /> One of the main objectives of the present study was to develop an electrohydrodynamic (EHD) ion-drag micropump with LN2 as the working liquid. EHD ion-drag pumping phenomenon refers to liquid motion caused by an interaction between electric and hydrodynamic fields in a dielectric liquid.<br /> To investigate the effect of each design parameter on the performance of the micropump, several prototypes with four distinct designs were fabricated and packaged. The designs included a variety of emitter shapes, inter-electrode spacings, electrode-pair spacings, and channel heights. The micropumps were tested at different DC voltages ranging from 0 to 2.5 kV. Two test rigs with novel measurement techniques were also designed, built, and calibrated to measure the generated static pressure head, electric current, and flow rate with an acceptable level of accuracy.<br /> The relationships between pressure/current (P-I) and pressure/voltage (P-V) for various designs were investigated experimentally. The results showed good agreement with the general analytical trends reported for EHD pumping in the literature. The experimental results also demonstrated that electrode geometry and gaps are effective in determining the pressure onset voltage. The results also show that a maximum static pressure head of 160 Pa at 1400 V is achievable for a design with a combination of a 50-μm emitter-collector gap, a 200-μm electrode-pair gap, and a saw-tooth shaped emitter/flat collector.