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Electric field-assisted technologies show prospects for heat removal in electronic cooling scenarios with electro-thermo-convection phenomena. The coupled multiphysics field model is built using the finite volume method, and two configurations (depending upon the orientation of the electric field and gravity) are investigated for different shear-thinning properties and polymer elasticities. The results demonstrate a remarkable impact on the heat exchange efficiency, energy budget, plume morphology, and force distribution features. Two key partitions (buoyancy or Coulomb force-dominated regions) can be divided by Rayleigh number Ra ≤ 103 and electric Reynolds number R e E ≤ 1.57. A heat transfer boost of 13.9 times and 5.0 times was obtained in the two arrangements vs no electric reinforcement. The shear-thinning shows a noticeable positive contribution, and the heat transfer efficiency can be modulated by polymer elasticity within a wide parameter range. A detailed evaluation of the interfacial forces reveals the nonmonotonic curves of fluid convection and energy inputs. [ABSTRACT FROM AUTHOR]

The mechanisms of a charge injection-induced electrohydrodynamic pump using the lattice Boltzmann method are numerically investigated in this paper. The pump is composed of a dielectric liquid layer and two substrate layers with embedded electrodes. There are three possible flow modes found, which are associated with the generation of local convective rolls for different electrode arrangements, namely, modes associated with one and two vortices and an irrotational mode. For different flow modes, results are presented for both the transient development of the flow field and the steady-state total flow rate and pressure. A distinct four-state transition can be observed in the temporal record of the velocity field. Regarding pumping ability, it is found that the irrotational mode can lead to optimal performance, while the single-vortex flow mode gives the worst performance. [ABSTRACT FROM AUTHOR]

The direction of coupled buoyancy and electric forces has a significant effect on both the fluid flow and heat transfer in an electro-thermo-convection (ETC) system. Here, we theoretically and numerically investigate the instability and bifurcations of ETC inside a tilted square cavity. A linear stability analysis is conducted using a unified linearized-lattice Boltzmann model by solving the coupled linear Navier–Stokes equation, linear Poisson equation, linear Nernst–Planck equation, and the linear energy equation. The numerical simulation is performed by integrating our code with the Palabos library. Results show that the interactions between the stabilizing buoyancy force and electric force lead to a Hopf bifurcation for Rayleigh number Ra = 1 × 105. The steady flow transitions to a traveling-wave flow by a subcritical bifurcation when tilted angles are less than δc ∈ [48°,49°]. For tilted angles above δc, the flow loses its stability through a local oscillation caused by a supercritical bifurcation. Finally, the chaotic behavior is quantitatively analyzed through the calculation of the Lyapunov exponent, which increases linearly with the electric Rayleigh number and is weakly dependent on the tilted angle. [ABSTRACT FROM AUTHOR]

Due to the Onsager–Wien effect (enhanced electric field dissociation), electrohydrodynamic (EHD) conduction pumping problems in the Oldroyd-B viscoelastic dielectric liquid are solved using the finite volume method. Fully coupled nonlinear equations, including the Naiver–Stokes (N–S) equation, the Nernst–Plank equation of the ion conduction mechanism, and the constitutive equation of viscoelastic fluid, are thoroughly implemented. Our numerical model is fully verified with two benchmark cases, and simulations are performed under different conduction numbers C0 (0.01–103), Weissenberg numbers Wi (0.01–50), and viscosity ratios (0.3–0.9). Two limiting operating states of EHD conduction pumping, the Ohmic and the saturation regimes, are discussed in detail. Elastic instability is more likely to occur in the Ohmic regime, and the thickness of the heterocharge layer (called the dissociation layer) remains sensitive to C0 and the elasticity values. Current density and pressure generation show crucial degrees of dependence on the fluid elasticity and viscosity ratio. [ABSTRACT FROM AUTHOR]

The transition process from laminar to chaotic flow in electro-thermal convection of a dielectric liquid is numerically investigated using a unified lattice Boltzmann method. The liquid is confined in a closed square cavity, and free charges are introduced into the system through a strong unipolar injection mechanism. Three cases with different Rayleigh numbers are considered. With the increase of electric Rayleigh number, various complicated dynamical behaviors are observed and three diverse transition routes to chaos are identified, namely, the quasi-periodic sequence involving four incommensurable frequencies, the intermittency sequence, and the alternating periodic-chaotic sequence. Numerical results are illustrated using time histories, Fourier frequency spectra, and phase portraits. The chaotic behavior is quantitatively analyzed through the calculation of fractal dimension and Lyapunov exponent. Typical flow patterns for both steady-state regime and periodic regime are also presented and discussed. [ABSTRACT FROM AUTHOR]

Highlights • Oscillatory flow of electro-thermo-convection in eccentric annulus is studied for the first time. • A unified lattice Boltzmann model is adopted to solve the whole set of governing equations. • Results are presented for different control parameters and radius ratio. • The flow undergoes steady state, periodic oscillation and chaotic state as electric Rayleigh number increase. • The formation of oscillating flows is strongly related to the value of radius ratio. Abstract A detailed numerical investigation for oscillatory electro-thermo-convection of dielectric liquids in horizontal eccentric annulus is carried out based on a unified lattice Boltzmann method (LBM). The liquid is under the simultaneous action of a strong unipolar charge injection and a thermal gradient. The self-oscillatory behaviors and heat transfer characteristics for different Rayleigh number Ra , electric Rayleigh number T , Prandtl number Pr , mobility parameter M and radii ratio are studied systematically. The results show that the values of Ra within the range from 103 to 104 have little effect on the periodic oscillatory convection, while the flow develops from steady to periodic oscillatory and finally evolves into chaotic as T increases, and the fundamental frequency and the fluctuation amplitude as well as the heat transfer rate increase with T. Moreover, it is found that the fluid properties have significant impact on the oscillatory convection, and the formation of oscillating flows is strongly related to the value of radius ratio. [ABSTRACT FROM AUTHOR]

The externally imposed direct current (DC) electric field mightily impacts on the conjugate heat transfer existing somewhere between the solid and liquid phases, which is numerically investigated via Lattice Boltzmann method (LBM) in this paper. The model is a square cavity filled with dielectric liquid, in which has a centred heat-generating solid body, and the spatially inhomogeneous physical properties such as thermal conductivity, heat capacity, permittivity and mobility are considered distinctively. The lattice Boltzmann method is used to solve the entirely coupled equations and the developed code is first verified by three cases for the hydrostatic solution, conjugate heat transfer with and without heat source. The LBM results show the highly agree well with both the derived analytical solution and the results obtained by other papers. Then, enhancement effect of the flow and heat transfer when electrohydrodynamic (EHD) forces in existence are studied under the different governing parameters and the internal heat source intensity. It is found that the solid-liquid two phases conjugate heat transfer can be significantly enhanced when applying a DC electric field across the domain. [ABSTRACT FROM AUTHOR]

Experiments on the electrohydrodynamic (EHD) flow characteristics of a dielectric liquid in a sharp needle-plate configuration under direct current (DC) and alternating current (AC) electric field are carried out. The current-voltage characteristics and the velocity field are simultaneously recorded for understanding the flow behavior and its mechanism. For the DC case, a critical voltage separating the conduction and injection regimes and the corresponding flow reverse is observed. Results indicate the polarity of voltage only influences the flow's intensity in the injection regime. For the AC case, two types of signals with the same 50% duty cycle are considered. For the pulsed voltage (−2.0kV to 0), the flow generally keeps the plume structure and shows weaker strength than the corresponding DC case. For the AC signal (-2.0kV–+2.0kV), the velocity amplitude first decreases and then tends to be constant with the increase of frequency. The weak flow motion with high frequency AC field is due to conduction. • EHD flow characteristics of liquid under DC and AC electric field are investigated. • The influence of DC polarity on charge generation mechanisms is studied. • The velocity field of liquid under applied different AC signals is reported. [ABSTRACT FROM AUTHOR]