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Cunlu Zhao

Publications and source records attributed to Cunlu Zhao.

8 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

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↗
arXiv2015

Electroosmosis in conducting nanofluidic channels

Theoretical modeling of electroosmosis through conducting (ideally polarizable) nanochannels is reported. Based on the theory of induced charge electrokinetics, a novel nanofluidic system which possesses both adjustable ion selective characteristics and flexible flow control is proposed. Such nanofluidic devices operate only with very low gate control voltage applied on the conductive walls of nanochannels, and thus even can be energized by normal batteries. We believe that it is possible to use such metal-electrolyte configurations to overcome the difficulties met with conventional metal-isolator-electrolyte systems for nanofluidic applications.

physics.flu-dyn↗
arXiv2015

Electroosmotic mobilities of non-Newtonian fluids

Numerical analyses of transient electro-osmosis of a typical non-Newtonian liquid induced by DC and AC electric fields in a rectangular microchannel are conducted in the framework of continuum fluid mechanics. The famous power-law constitutive model is used to express the fluid dynamic viscosity in terms of the velocity gradient. Transient start-up characteristics of electro-osmotic power-law liquid flow in rectangular microchannels are simulated by using finite element method. Under a DC electric field, it is found out and the fluid is more inert to the external electric field and the steady-state velocity profile becomes more plug-like with decrease of the flow behavior index of the power-law liquids. The numerical calculations also confirm the validity of the generalized Smoluchowski slip velocity which can serve as the counterpart for the classic Smoluchowski slip velocity when dealing with electrokinetic flow of non-Newtonian power-law fluids. Under AC electric fields, the fluid is more obviously accelerated during oscillations and the amplitude of the oscillating velocity is closer to the magnitude of the generalized Smoluchowski velocity as the fluid behavior index increases. These dynamic predictions are of practical significance for the design of microfluidic devices that manipulate non-Newtonian fluids such as biofluids, polymer solutions and colloidal suspensions.

physics.flu-dyn↗
arXiv2015

Numerical analysis of dynamic electro-osmotic flows of non-Newtonian fluids in rectangular microchannels

Numerical analyses of transient electro-osmosis of a typical non-Newtonian liquid induced by DC and AC electric fields in a rectangular microchannel are conducted in the framework of continuum fluid mechanics. The famous power-law constitutive model is used to express the fluid dynamic viscosity in terms of the velocity gradient. Transient start-up characteristics of electro-osmotic power-law liquid flow in rectangular microchannels are simulated by using finite element method. Under a DC electric field, it is found out and the fluid is more inert to the external electric field and the steady-state velocity profile becomes more plug-like with decrease of the flow behavior index of the power-law liquids. The numerical calculations also confirm the validity of the generalized Smoluchowski slip velocity which can serve as the counterpart for the classic Smoluchowski slip velocity when dealing with electrokinetic flow of non-Newtonian power-law fluids. Under AC electric fields, the fluid is more obviously accelerated during oscillations and the amplitude of the oscillating velocity is closer to the magnitude of the generalized Smoluchowski velocity as the fluid behavior index increases. These dynamic predictions are of practical significance for the design of microfluidic devices that manipulate non-Newtonian fluids such as biofluids, polymer solutions and colloidal suspensions.

physics.flu-dyn↗
arXiv2010

AC electrokinetic phenomena over semiconductive surfaces: effective electric boundary conditions and their applications

Electrokinetic boundary conditions are derived for AC electrokinetic (ACEK) phenomena over leaky dielectric (i.e., semiconducting) surfaces. Such boundary conditions correlate the electric potentials across the semiconductor-electrolyte interface (consisting of the electric double layer (EDL) inside the electrolyte solutions and the space charge layer (SCL) inside the semiconductors) under AC electric fields with arbitrary wave forms. The present electrokinetic boundary conditions allow for evaluation of induced zeta potential contributed by both bond charges (due to electric polarization) and free charges (due to electric conduction) from the leaky dielectric materials. Subsequently, we demonstrate the applications of these boundary conditions in analyzing the ACEK phenomena around a semiconducting cylinder. It is concluded that the flow circulations exist around the semiconducting cylinder and are shown to be stronger under an AC field with lower frequency and around a cylinder with higher conductivity.

physics.flu-dyn↗