Search Results (4)

In this article, electro-osmotic thrusters (EOTs), which are full of non-Newtonian power-law fluids with a flow behavior index n of the effective viscosity, are theoretically investigated in a microchannel. Different values of the flow behavior index represent two kinds of non-Newtonian power-law fluids, pseudoplastic fluids (n < 1) and dilatant fluids (n > 1), which have not yet been considered to be used as propellants in micro-thrusters. Analytical solutions of the electric potential and flow velocity are obtained using the Debye–Hückel linearization assumption and the approximate scheme of hyperbolic sine function. Then, thruster performances of power-law fluids, including specific impulse, thrust, thruster efficiency, and thrust-to-power ratio, are explored in detail. Results show that these performance curves strongly depend on the flow behavior index and electrokinetic width. It is noted that the non-Newtonian pseudoplastic fluid is most suitable as a propeller solvent in micro electro-osmotic thrusters owing to its improving or optimizing deficiencies in the performances of the existing Newtonian fluid thrusters. Full article

Here, space electroosmotic thrusters in a rigid nanochannel with high wall zeta potentials are investigated numerically, for the first time, considering the effect of finite size of the ionic species. The effect, which is called a steric effect, is often neglected in research about micro/nano thrusters. However, it has vital influences on the electric potential and flow velocity in electric double layers, so that the thruster performances generated by the fluid motion are further affected. These performances, including thrust, specific impulse, thruster efficiency, and the thrust-to-power ratio, are described by using numerical algorithms, after obtaining the electric potential and velocity distributions under high wall zeta potentials ranging from −25.7 mV to −128.5 mV. As expected, the zeta potential can promote the development of thruster performances so as to satisfy the requirement of space missions. Moreover, for real situation with consideration of the steric effect, the thruster thrust and efficiency significantly decrease to 5–30 micro Newtons and 80–90%, respectively, but the thrust-to-power ratio is opposite, and expends a short specific impulse of about 50–110 s. Full article

The influence of steric effects on the performances of space electroosmotic thrusters (EOTs) was numerically delineated in soft nanochannels for which its walls are covered with polyelectrolyte materials. The size effect of the ionic species, namely the steric effect, is neglected in many previous research studies, but it has vital influences on electrostatic potential and electroosmotic velocity, which is further introduced into the present study in order to understand and improve the exploration of nano electroosmotic thrusters with soft channels. The thruster’s thrust, specific impulse, total input power, thruster efficiency and thrust-to-power ratio are computed based on finite difference methods. It is found that the thruster’s thrust and specific impulse increase with the steric parameter while the efficiency and thrust-to-power ratio possess opposite trends due to the enhancement of Joule heating dissipation. For real situations with the consideration of ion size, although the thruster’s thrust could be promoted, the efficiency is only 30–70%, and the peak values of thrust-to-power ratio fade away. Full article

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. Full article