Space Electroosmotic Thrusters in Ion Partitioning Soft Nanochannels

Abstract

Space electroosmotic thrusters (EOTs) are theoretically investigated in a soft charged nanochannel with a dense polyelectrolyte layer (PEL), which is considered to be more realistic than a low-density PEL. When the PEL is dense, its permittivity is smaller than the one of the electrolyte solution layer, leading to rearrangement of ions in the channel, which is denoted as the ion partitioning effect. It is noted that fluid viscosity becomes high within the PEL owing to the hydration effect. An analytical solution for electroosmotic velocity through the channel is obtained by utilizing the Debye–Hückel linearization assumption. Based on the fluid motion, thruster performances, including thrust, specific impulse, thrust-to-power ratio, and efficiency, are calculated. The ion partitioning effect leads to enhancement of the thruster velocity, while increase of the dynamic viscosity inside the PEL reduces the flow rate of the fluid. Therefore, these performances are further impacted by the dense soft material, which are discussed in detail. Moreover, changes or improvements of the thruster performances from the dense PEL to the weak PEL are presented and compared, and distributions of various energy items are also provided in this study. There is a good result whereby the increase in electric double layer thickness promotes the development of thruster performances. Ultimately, the simulated EOTs produce thrust of about 0 to 20 μN and achieve thruster efficiency of 90.40%, while maintaining an appropriate thrust–power ratio of about 1.53 mN/W by optimizing all design parameters.

Steric Effects on Space Electroosmotic Thrusters in Soft Nanochannels

“…Moreover, the applied axial electric field is set as 5 × 10 8 V/m with a voltage drop between the electrodes of 500 V for a 1 µm length channel, which is for producing the needed force and energy for space propulsion. The value of the voltage drop as high as 500-700 V has been used in molecular dynamic simulations of EOF for water solutions [5,6,20,21,40,41,48]. As the steric factor is zero, the problem becomes independent of the steric effect, which has been performed in previous studies [20].…”

“…We had considered the influence of soft nanochannel on the electroosmotic thrusters and found that the thruster could achieve efficiency up to 90% and deliver thrust at about 0-20 µN when the soft material was dense [20,21]. When the PEL is dense, its dielectric permittivity is lower than the bulk aqueous medium, resulting in the rearrangement of ions in the channel, which is denoted as the ion partitioning effect.…”

“…Based upon the distributions of the electric potential and flow velocity, the variations of thruster performances are obtained and analyzed by finite difference methods. Our main purpose is not only to understand the reality that there are size effects of ions in the electrolyte solution but also to understand and improve the exploration of thruster performances with soft nanochannels [20,21].…”

Improved ionic current rectification utilizing cylindrical nanochannels coated with polyelectrolyte layers of non-uniform thickness

“…Nanopores, nanopipettes, and nanochannels have various applications such as in biological sensing, 1,2 biological separation, 3 energy conversion, 4,5 water desalination, 6 etc. Accordingly, the understanding and control of the transport phenomena, especially ionic transport, in such elements have been the subject of many research studies during the past two decades.…”

Micro Electro-Osmotic Thrusters of Power-Law Fluids for Space Propulsion

“…Huang and Huang [ 15 ] further combined nano electrokinetic thrusters with two-liquid electro-osmotic flows and analyzed performances of the thrusters under the small wall zeta potential. Zheng and Jian [ 16 , 17 ] investigated the influence of the soft nanochannel on the electro-osmotic thrusters and found that the thruster could achieve an efficiency as high as 90% and deliver a thrust of about 0–20 μN.…”