ELECTROHYDRODYNAMICS (EHD) PUMPING OF LIQUID NITROGEN APPLICATION TO SPOT CRYOGENIC COOLING OF SENSORS AND DETECTORS

Abstract

Superconducting electronics require cryogenic conditions as well as certain conventional electronic applications exhibit better performance at low temperatures. A cryogenic operating environment ensures increased operating speeds and improves the signal-to-noise ratio and the bandwidth of analog devices and sensors, while also ensuring reduced aging effect. Most of these applications require modest power dissipation capabilities while having stricter requirements on the spatial and temporal temperature variations. Controlled surface cooling techniques ensure more stable and uniform temporal and spatial temperature distributions that allow better signal-to-noise ratios for sensors and elimination of hot spots for processors. EHD pumping is a promising technique that could provide pumping and mass flow rate control along the cooled surface. In this work, an ion-drag EHD pump is used to provide the pumping power necessary to ensure the cooling requirements.

The present study contributes to two major areas which could provide significant improvement in electronics cooling applications. One direction concerns development of an EHD micropump, which could provide the pumping power for micro-cooling systems capable of providing more efficient and localized cooling. Using a 3M fluid, a micropump with a 50 mm gap between the emitter and collector and a saw-tooth emitter configuration at an applied voltage of about 250 V provided a pumping head of 650 Pa. For a more optimized design a combination of saw tooth emitters and a 3-D solder-bump structure should be used.

The other major contribution involves the application, for the first time, of the EHD pumping technique to cryogenic liquids. Successful implementation of these cooling techniques could provide on-demand and on-location pumping power which would allow tight cryogenic temperature control on the cooling surface of sensors, detectors and other cold electronics. Pumping heads of up to 1 Pa with mass flow rates of 0.8 g/s were achieved using liquid nitrogen. Although the pressure head results seem relatively small, the corresponding liquid nitrogen mass flow rate meets the targeted heat removal requirements specific to superconducting sensors and detectors.