Development of an electrohydrodynamic injection micropump and its potential application in pumping fluids in cryogenic cooling systems

Cryogenic cooling has become a widely adopted technique to improve the performance of electronics and sensors. A potential application of an electrohydrodynamic (EHD) pumping system is its use in pumping fluids in cryogenic cooling systems. In this paper, we present the results of a theoretical/experimental investigation to study the feasibility of using an EHD injection micropump for pumping liquid nitrogen. First, the mechanisms of charge transport and ionization phenomenon in cryogenic liquids are discussed. Next, the design and fabrication of an EHD injection micropump that employs an array of interdigitated saw-tooth/plane electrodes are described. Finally, experimental results and observations are presented. An asymmetric saw-tooth/plane geometry was designed to achieve a strong inhomogeneous electric field. Each emitter electrode had a base width of 10 /spl mu/m. Each tooth on the emitter electrode had a base length of 10 /spl mu/m with a tip angle of 60/spl deg/. The collector electrode consisted of a planar strip with a width of 10 /spl mu/m. The gap between emitter and collector electrodes was 20 /spl mu/m. The distance between each neighboring stage (a pair of emitter and collector electrodes) was 40 /spl mu/m. The patterned area was 10 mm by 20 mm allowing approximately 200 stages to be fabricated along the length of the micropump. The maximum pressure head achieved by this micropump in the absence of a net flow was 550 and 205 Pa for 3M's HFE-7100 thermal fluid and liquid nitrogen, respectively. Also, the maximum mass flow rate was 3.9 g/min at the generated pressure of 180 Pa during a closed loop test with HFE-7100.