arXiv subjects

Qiuwang Wang

Publications and source records attributed to Qiuwang Wang.

4 recordsLinked to original sources

arXiv2023

Thermoelectric effect and temperature-gradient-driven electrokinetic flow of electrolyte solutions in charged nanocapillaries

A systematic theoretical study of thermoelectric effect and temperature-gradient-driven electrokinetic flow of electrolyte solutions in charged nanocapillaries is presented. The study is based on a semianalytical model developed by simultaneously solving the non-isothermal Poisson-Nernst-Planck-Navier-Stokes equations with the lubrication theory. Particularly, this paper clarifies the interplay and relative importance of the thermoelectric mechanisms due to (a) the convective transport of ions caused by the fluid flow, (b) the dependence of ion electrophoretic mobility on temperature, (c) the difference in the intrinsic Soret coefficients of cation and anion. Additionally, synergy conditions for the three thermoelectric mechanisms to fully cooperate are proposed for thermo-phobic/philic electrolytes. The temperature-gradient-driven electrokinetic flow is shown to be a nearly unidirectional flow whose axial velocity profiles vary with the axial location. Also, the flow can be regarded as a consequence of the counteraction or cooperation between a thermoelectric-field-driven electroosmotic flow and a thermo-osmotic flow driven by the osmotic pressure gradient and dielectric body force. Moreover, the Seebeck coefficient and the fluid average velocity are demonstrated to be affected by electrolyte-related parameters. The results are beneficial for understanding the temperature-gradient-driven electrokinetic transport in nanocapillaries and also serve as theoretical foundation for the design of low-grade waste heat recovery devices and thermoosmotic pumps.

physics.flu-dyn↗

arXiv2023

Simultaneous thermoosmotic and thermoelectric responses in nanoconfined electrolyte solutions: Effects of nanopore structures and membrane properties

Hypothesis: Nanofluidic systems provide an emerging and efficient platform for thermoelectric conversion and fluid pumping with low-grade heat energy. As a basis of their performance enhancement, the effects of the structures and properties of the nanofluidic systems on the thermoelectric response (TER) and the thermoosmotic response (TOR) are yet to be explored. Methods: The simultaneous TER and TOR of electrolyte solutions in nanofluidic membrane pores on which an axial temperature gradient is exerted are investigated numerically and semi-analytically. A semi-analytical model is developed with the consideration of finite membrane thermal conductivity and the reservoir/entrance effect. Findings: The increase in the access resistance due to the nanopore-reservoir interfaces accounts for the decrease of short circuit current at the low concentration regime. The decrease in the thermal conductivity ratio can enhance the TER and TOR. The maximum power density occurring at the nanopore radius twice the Debye length ranges from several to dozens of mW K$^{-2}$ m$^{-2}$ and is an order of magnitude higher than typical thermo-supercapacitors. The surface charge polarity can heavily affect the sign and magnitude of the short-circuit current, the Seebeck coefficient, and the open-circuit thermoosmotic coefficient, but has less effect on the short-circuit thermoosmotic coefficient. Furthermore, the membrane thickness makes different impacts on TER and TOR for zero and finite membrane thermal conductivity.

cond-mat.soft↗

arXiv2023

Ion steric effect induces giant enhancement of thermoelectric conversion in electrolyte-filled nanochannels

Ionic thermoelectricity in nanochannels has received increasing attention because of its advantages such as high Seebeck coefficient and low cost. However, most studies have focused on dilute simple electrolytes that neglect the effects of finite ion sizes and short-range electrostatic correlation. Here, we reveal a new thermoelectric mechanism arising from the coupling of ion steric effect due to finite ion sizes and ion thermodiffusion in electric double layers, using both theoretical and numerical methods. We show that this mechanism can significantly enhance the thermoelectric response in nanoconfined electrolytes, depending on the properties of electrolytes and nanochannels. Compared to the previously known mechanisms, the new mechanism can increase the Seebeck coefficient by 100\% or even one order of magnitude enhancement under optimal conditions. Moreover, we demonstrate that the short-range electrostatic correlation can help preserve the Seebeck coefficient enhancement in weaker confinement or in more concentrated electrolytes.

cond-mat.soft↗

arXiv2019

Temperature-gradient-induced electrokinetic flow and thermoelectricity of electrolyte solutions in a capillaries

A systematic theoretical study of temperature-gradient-induced electrokinetic flow and thermoelectric potential of electrolyte solutions in a micro-/nanocapillary is presented. The study is based on a semi-analytical model developed by simultaneously solving the energy equation and the Poisson-Nernst-Planck/Navier-Stokes equations with the lubrication theory. The semi-analytical model is shown to be mainly governed by eight parameters, including two temperature-related parameters (temperature and its gradient), two electrokinetic parameters ($ζ$ potential and the ratio of capillary radius to the Debye length $κ_0a$) and four physical properties of cation and anion (i.e. Soret coefficient difference $ΔS_T$, average Soret coefficient $S_T$, normalized difference in diffusivities $χ$ and intrinsic Peclet number $λ$). It is found that the thermoelectric field is induced by three effects, which are respectively due to (1) the difference in the Soret coefficients of cation and anion; (2) the selective ion diffusion resulting from the temperature-modified Boltzmann distribution of ions; (3) the advective transport of ions caused by the fluid flow. The first thermoelectric effect prevails for lower $ζ$ potentials or large $κ_0a$, while the second is dominant for higher $ζ$ potentials with very small $κ_0a$. The first two thermoelectric effects can cooperate or counteract depending on the sign of $ζΔS_T$. Finally, the temperature-gradient-induced electrokinetic flow is found to be a superposition of an electroosmotic flow component due to the thermoelectric field and a thermoosmotic flow component due to the combined effects of osmotic pressure and dielectric body force. These two flow components may cooperate or counteract depending on values of $ζ$ and $κ_0a$.

physics.flu-dyn↗