Miniature, metal 3D-printed, multiplexed electrohydrodynamic gas pumps

Abstract

We report the design, fabrication, and experimental characterization of the first additively manufactured, miniature, metal multi-needle ionic wind pumps in the literature. The pumps are needle-ring corona diodes composed of a monolithic inkjet binder-printed active electrode, made in stainless steel 316L, with five sharp, conical needles, and a thin plate counter-electrode, made in copper, with electrochemically etched apertures aligned to the needle array; by applying a large bias voltage across the diode, electrohydrodynamically driven airflow is produced. The influence of tip multiplexing and tip sharpening on the ion current, airflow velocity, volumetric flow rate, and kinetic conversion efficiency of the pumps was characterized under different interelectrode separations, counter-electrode aperture diameters, and applied bias voltages, while triggering a negative corona discharge. At the optimal operating bias voltage (7.4 kV), the as-printed five-needle ionic wind pumps eject air at 2.66 m s−1 and at a volumetric flow rate of 316 cm3 s−1 –a twofold larger than the flow rate of an as-printed single-needle device and with 35% higher efficiency (i.e. 0.27%). Using a two-step electropolishing procedure, the needles of the active electrode can be uniformly sharpened down to 83.4 μm average tip diameter, i.e. about one quarter of their as-printed dimension (∼300 μm). Operated under the same conditions, the electropolished five-needle pumps eject air at 3.25 m s−1, i.e. 22% higher speed compared to the as-printed devices, with the same kinetic conversion efficiency. A two-module model was built in COMSOL Multiphysics, consisting of a three-species corona discharge module and a gas dynamics module, to gain insights into the operation of the pumps and to determine trends for increasing device performance. The electrohydrodynamic (EHD) body force calculated using this model has the same periodic behaviour of the Trichel pulse current. A time-dependent EHD body force analysis was performed, and the stabilized forces averaged over a multiple of the Trichel pulse period were used to predict the large-timescale airflow. The EHD force from the corona simulation can be rescaled to calculate the flow at different bias voltages, greatly reducing the simulation time, and making possible to systematically study the relevant parameters and optimize the design of the air pump. The experimental data agree with the simulation results and the reduced-order modelling.