Search

This article deals with the electromagnetohydrodynamic (EMHD) flow through a microchannel with three-dimensional corrugated walls where the fluid is driven by non-uniform electric field and uniform magnetic field. The three-dimensional corrugations are depicted by the product of two sinusoid functions with small amplitude e and wave numbers α and β in two horizontal directions. The analytic expressions of the electric potentials, velocities and volume flow rates are deduced by utilizing the perturbation method. The impacts of the corrugations on the electric potentials, the EMHD velocities and volume flow rates are discussed. Moreover, the influences of relevant parameters, including Hartmann number Ha, aspect ratio χ (χ=β/α) of the corrugations and the parameter R (R=β·α) on the flow are analyzed. Furthermore, the comparisons of the flow rates with experimental data are performed. The results show that the maximum flow rate can be obtained by increasing magnetic field strength parameter Ha or adjusting the phases of the wavy walls.

In this paper, the separation of variables method is applied to investigate the effects of solution pH, background salt concentration and AC electric field frequency on time periodic electroosmotic flow in a pH-regulated parallel-plate nanochannel. The surface charge is generated by the protonation and deprotonation of the functional group SiOH. The background salt is KCl. The pH value of the solution is adjusted by HCl and KOH. Analytical and semi-analytical solutions for electric potential and velocity distributions are obtained. The results show that the electric potential caused by the electric double layer depends greatly on the solution pH and background salt concentration. The amplitudes of the velocity and flow rate of the time periodic electroosmotic flow decrease with the background salt concentration and increase with the deviation of the solution pH from the isoelectric point. In a nanochannel having a height less than 100 nm, the electroosmotic velocity amplitude is not affected by the AC electric field frequency because the oscillating Reynolds number is much less than unity.

Perturbation solutions for the velocity and electric potential of a time periodic magnetohydrodynamic slip flow in a microchannel with sinusoidal wall corrugations are obtained using perturbation method. The effects of wall corrugations, slip length, Hartmann number and the frequency of the electric potential on the flow are analyzed theoretically and graphically. The results show that velocity and electric potential are significantly disturbed by wall roughness and that there exists a phase lag between the velocity and the electric potential. The velocity profile is characterized by the ratio of momentum diffusion time scale to the period of the applied electric field. The phase lag increases with frequency, slip length and decreases with Hartmann number, the wavenumber and phase difference of the wall corrugations. However, for a sufficiently small frequency, the phase lag is almost nonexistent. The effect of the phase difference of the wall corrugations on the phase lag becomes unimportant when the wavenumber is larger than 2. The velocity amplitude increases with slip length and decreases with frequency, wavenumber and phase difference. However, the phase difference becomes unimportant for sufficiently large wavenumber. When the frequency is large enough, the velocity amplitude is not influenced by slip length.

By using the method of separation of variables, an analytical solution for the magnetohydrodynamic (MHD) flow of the generalized Maxwell fluids under AC electric field through a two-dimensional rectangular micropump is reduced. By the numerical computation, the variations of velocity profiles with the electrical oscillating Reynolds number Re , the Hartmann number Ha , the dimensionless relaxation time De are studied graphically. Further, the comparison with available experimental data and relevant researches is presented.

In this paper, 2D electromagnetohydrodynamic (EMHD) flow in a microparallel channel with slightly transverse corrugated walls is investigated using perturbation method. The corrugations of the two walls are presented by periodic sinusoidal waves with small amplitudes. The perturbation solutions of the stream function and a relation between flow rate and roughness are obtained. It is shown that the flow rate always decreases due to the wall corrugations irrespective of the phase difference. For prescribed Hartmann number and wave number of the wavy walls, the flow resistance increases as the phase difference between the wall corrugations increases. The effect of corrugation on the flow rate decreases with Hartmann number. With the increase of wave number, the effects of corrugations on the flow rate increase. The phase difference of wall corrugations becomes unimportant when the wave number is greater than 4. The obtained results for the flow rates as a function of the applied current are in qualitative agreement with the existing experimental results.

In this paper we analytically investigate the electroviscous effect and electrokinetic energy conversion in the time periodic pressure-driven flow of an incompressible viscous Newtonian liquid through a parallel-plate nanochannel with surface charge-dependent slip. Analytical and semi-analytical solutions for electric potential, velocity and streaming electric field are obtained and are utilized to compute electrokinetic energy conversion efficiency. The results show that velocity amplitude and energy conversion efficiency are reduced when the effect of surface charge on slip length is considered. The surface charge effect increases with zeta potential and ionic concentration. In addition, the energy conversion efficiency is large when the ratio of channel half-height to the electric double layer thickness is small. The boundary slip results in a large increase in energy conversion. Higher values of the frequency of pressure pulsation lead to higher values of the energy conversion efficiency. We also obtain the energy conversion efficiency in constant pressure-driven flow and find that the energy conversion efficiency in periodical pressure-driven flow becomes larger than that in constant pressure-driven flow when the frequency is large enough.

In this paper, a perturbation method is introduced to study the EOF in a microparallel channel with 3D wall roughness. The corrugations of the two walls are periodic sinusoidal waves of small amplitude in two directions either in phase or half-period out of phase. Based on linearized Poisson-Boltzmann equation, Laplace equation, and the Navier-Stokes equations, the perturbation solutions of velocity, electrical potential, and volume flow rate are obtained. By using numerical computation, the influences of the wall corrugations on the mean velocity are analyzed. The variations of electrical potential, velocity profile, mean velocity, and their dependences on the wave number α and β of wall corrugations in two directions, the nondimensional electrokinetic width K, and the zeta potential ratio between the lower wall and the upper wall ς are analyzed graphically.

In this paper a perturbation method is introduced to study the electromagnetohydrodynamic (EMHD) flow in a microparallel channel with slightly corrugated walls. The corrugations of the two walls are periodic sinusoidal waves of small amplitude either in phase or half-period out of phase, and the perturbation solutions of velocity and volume flow rate are obtained. Using numerical computation the effects of the corrugations on the flow are graphically analysed. The results show that the influence of corrugation on the flow decreases with Hartmann number. The phase difference of wall corrugations becomes unimportant when the wavenumber is greater than 3 or when the Hartmann number is greater than 4. With the increase in wavenumber, the decreasing effects of corrugations on the flow increase. When the wavenumber is smaller than the threshold wavenumber (it is a function of Hartmann number) and the wall corrugations are half-period out of phase, the corrugations can enhance the mean velocity of EMHD flow. However, the mean velocity is always decreased when the corrugations are in phase.