Highly Efficient Electrohydrodynamic Pumping: Molecular Isomer Effect of Dielectric Liquids, and Surface States of Electrodes

Abstract

Highly efficient electrohydrodynamic (EHD) pumping was obtained by a combination of a dielectric liquid having a molecular isomer and electrodes with a smooth surface. Four kinds of surface states of Cu electrodes were processed by conventional mechanical polishing, fine diamond paste polishing, chemical etching and Au vapor deposition. A series of hydrofluoroether liquids (HFEs) were used as dielectric liquids: C3F7OCH3 (HFE-7000), C4F9OCH3 (HFE-7100), C4F9OC2H5 (HFE-7200), C6F13OCH3 (HFE-7300), and C5H5F6OC3HF6 (HFE-7600). The coexistence of normal (n-) and isomer (i-) HFEs and their molar fractions were examined by NMR spectroscopy. Among the dielectric liquids, the hybrid n- and i-HFE-7600 showed highly efficient EHD pumping, where the electric current, I, was sufficiently suppressed by the smooth surface of the electrodes. The maximum hydrostatic pressure Δpmax was ∼7500 Pa with 12 kV and I = 19 μA. The smooth surface of the electrodes contributes not only to the formation of a stable electric double layer (EDL) but also to the prevention of charge injection from the electrodes. Polarization pumping derived from the stable EDL enables highly efficient energy transfer without discharging, or damage to the sample and electrodes. The dipole moments of the HFEs were estimated by density functional theory calculations. The hydrostatic pressure was found to be proportional to the difference in the calculated dipole moment between n- and i-HFEs. Numerical simulations were carried out to examine the experimentally obtained electrode gap dependence of the hydrostatic pressure.

In-depth description of electrohydrodynamic conduction pumping of dielectric liquids: Physical model and regime analysis

“…Experimental studies by Jeong and Seyed-Yagoobi 7 have shown the effect of electrode geometry on pressure generation in more detail, with numerical models from Feng and Seyed-Yagoobi 23 showing the profiles of the heterocharge layers in perforated electrode geometries. Experimental studies by Mahmoudi et al 24 and Gharraei et al 25 have also shown the effect of different working fluids on pressure generations, and experimental studies by Abe et al 26 showed the effect of the surface characteristics of the electrodes on the pressure generation performance of an EHD conduction pump. It should be noted that the traditional efficiency of EHD conduction pumps in terms of flow generation (defined as the flow power generated divided by the input electric power) is very small since the transmission of electrical energy into pressure is not direct, but passes through the chemical reaction.…”

Hydrodynamic channeling as a controlled flow reversal mechanism for bidirectional AC electroosmotic pumping using glassy carbon microelectrode arrays

“…Here, various types of transmitters continuously transfer non-mechanical energy directly to the fluid to generate momentum. The most extensively studied dynamic approaches include thermal [6], electrohydrodynamic (EHD) [7], magnetohydrodynamic (MHD) [8], and DC and AC electroosmotic micropumps [9,10]. In this case, the lack of moving parts significantly simplifies the micropump structural framework, generally leading to a straightforward and cost-effective device fabrication process.…”