An experimental and theoretical study of laminar vortical flows driven by oscillating electromagnetic forces that act in orthogonal directions in a shallow electrolytic fluid layer is presented. Forces are generated by the interaction of the field of a dipolar permanent magnet and two imposed alternating electric currents perpendicular to each other with independent frequencies varying in the range of 10–30 mHz. Velocity fields of the time-dependent flow are obtained using particle image velocimetry, while particle tracking allows exploration of the Lagrangian trajectories and time maps. An approximate two-dimensional analytical solution is obtained for the laminar creeping regime so that Lagrangian trajectories are integrated explicitly. These trajectories resemble Lissajous figures with the usual property that, when the ratio of the frequencies of the imposed currents is rational, closed paths are found, while non-closed paths occur when this ratio is irrational. Deviations of this regime that account for slight increase of inertial effects are explored through a quasi-two-dimensional numerical simulation. In this case, non-closed paths are found even for rational frequency ratios. This case was observed in the experiment. Lagrangian trajectories calculated numerically show a qualitative agreement with experimental particle tracking. Furthermore, numerical time maps obtained for increasing inertial effects and rational frequency ratios reveal a chaotic behaviour. Some features of the Lagrangian trajectories are validated experimentally. In particular, topological properties of the calculated and observed time maps are in qualitative agreement. In a characteristic case, a partial time map calculated numerically is compared with the section acquired from the experimental tracking of one particle.

In this paper, we address the problem of heat and electric charge transport in a thermoelectric nanoscaled layer when an electric current is applied. The analysis is based on constitutive equations of the Maxwell-Cattaneo type describing the time evolution of dissipative flows with transport and thermoelectric coefficients depending on the width of the layer. This introduces memory and nonlocal effects and consequently a wave-like behaviour of system's temperature. We study the effects of the application of an electric current in two cases, namely, a constant current and a pulsed current. The time evolution of the system and the stationary state are determined. Besides the well known supercooling effect obtained when the electric pulse is applied, our results show the existence of a similar effect during the transient due to the wave-like behaviour of the temperature. The thermal figure of merit (TFM) is calculated at the minimum temperature reached during the supercooling, both in the transient and the pulsed regime. The maximum value of TFM in the transient reaches 114 improving the value of long length scale devices by a factor of 100. When the electric pulse is applied, TFM is improved by a factor of 20 over long length scale devices. We use the spectral methods of solution which assure a well representation of wave behaviour of heat and electric charge in short time scales given their spectral convergence.

The dynamics of vertically vibrating liquid drops has been studied by several researchers and different phenomena have been reported. In the present work, we report experimental results for some interesting phenomena that can be observed in a liquid drop subjected to vertical vibrations. For this purpose, a drop of Mercury was kept on a spherical watch glass and it was perturbed with different amplitudes and frequencies. The oscillations of the drop were recorded using a video camera and image analysis was used to further understand its behavior. The method of correlation was then employed to analyze the videos recorded with different perturbations. We report phenomena like subharmonic oscillations and rotation of the drop; and also the resonance and superpropulsion in the droplet ejection.

The flow generated by a free-moving magnet floating in a thin electrolyte layer is studied experimentally and numerically. The magnet is dragged by a traveling vortex dipole produced by a Lorentz force created when a uniform dc current injected in the electrolyte interacts with the magnetic field of the same magnet. The problem represents a typical case of fluid-solid interaction but with a localized electromagnetic force promoting the motion. Classical wake flow structures are observed when the applied current varies in the range of 0.2 to 10 A. Velocity fields at the surface of the electrolyte are obtained for different flow conditions through particle image velocimetry. Quasi-two-dimensional numerical simulations, based on the immersed boundary technique that incorporates the fluid-solid interaction, reproduce satisfactorily the dynamics observed in the experiments.

The time-dependent flow driven by electromagnetic forcing of an electrolytic fluid in the gap of a concentric spheres set-up is studied experimentally and theoretically. The driving Lorentz force is generated by the interaction of an alternating current radially injected through electrodes located at the equatorial zone of the spheres and a dipolar magnetic field produced by a permanent magnet inside the inner sphere. Experimentally, the time-dependent flows were explored in the laminar regime with a Reynolds number .