Miad Yazdani

Electrically Induced Dielectric Liquid Film Flow Based on Electric Conduction Phenomenon

Electrohydrodynamic (EHD) conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes, generated by the process of dissociation of the neutral electrolytic species and recombination of the generated ions. The theoretical formulation for EHD conduction pumping of liquid film is presented and fundamentally analyzed with the aid of numerical solutions. This model includes fluid dynamics governing equations under laminar and isothermal conditions which are modified to account for the presence of electric body force. The model also includes charge transport equations which are related to the dissociation/recombination phenomenon along with Maxwells relations that govern the electric field distribution. This paper determines how liquid film flow is generated based on the electric conduction phenomenon. Specifically, the role of controlling dimensionless parameters on the heterocharge layers and flow structures along with the impact of liquid film velocity on charge distribution are illustrated and fundamentally analyzed. In addition, the contribution of unique electrode designs toward electric body force distribution and flow pattern is investigated followed by the effect of interaction between adjacent electrode pairs in multi-pair configurations on generated flow rate. Further, a brief discussion of the conduction pumping efficiency is presented. Finally, the numerical results are verified against experimental data.

Numerical Investigation of Electrohydrodynamic-Conduction Pumping of Liquid Film in the Presence of Evaporation

Electrohydrodynamic (EHD) conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes, generated by the process of dissociation of the neutral electrolytic species and the recombination of the generated ions. This paper numerically investigates the EHD-conduction pumping of a liquid film in the presence of evaporation. The flow system comprises a liquid film flowing over a two-dimensional flat plate. The vapor phase above the flat plate is extended far beyond the interface. The channel is separated into four different sections: the entrance, electrode, evaporation, and downstream sections. The entrance, electrode, and downstream regions are adiabatic while a constant heat flux is applied in the evaporation section. The concept of EHD-conduction pumping of liquid film in the presence of phase change is numerically demonstrated in this paper. The resultant heat transfer due to conduction pumping is evaluated as well. The results for heat transfer coefficient along the channel indicate considerable improvement of heat transfer coefficient compared with the pressure-driven counterpart.

Heat Transfer Augmentation of Parallel Flows by Means of Electric Conduction Phenomenon in Macro- and Microscales

Electrohydrodynamic conduction phenomenon takes advantage of the electrical Coulomb force exerted on a dielectric liquid generated by externally applied electric field and dissociated charges from electrolytes. The electric conduction phenomenon can be applied to enhance or control mass transport and heat transfer in both terrestrial and microgravity environments with advantages of simplicity and no degradation of fluid properties for isothermal as well as nonisothermal liquids. This paper numerically studies the heat transfer augmentation of externally driven macro- and microscale parallel flows by means of electric conduction phenomenon. The electric conduction is generated via electrode pairs embedded against the channel wall to mainly enhance the heat transfer and not necessarily to pump the liquid. Two cases of Poiseuille and Couette parallel flows are considered where for the former, a constant external pressure gradient is applied along the channel and for the latter, the channel wall moves with a constant velocity. The electric field and electric body force distributions along with the resultant velocity fields are presented. The heat transfer enhancements are illustrated under various operating conditions for both macro- and microscales. DOI: 10.1115/1.4000977

Thermal Homogenization in Spherical Reservoir by Electrohydrodynamic Conduction Phenomenon

Effect of electric conduction phenomenon on the mixing mechanism is studied numerically to thermally homogenize a dielectric liquid with an initial nonuniform temperature distribution. The fluid is stored in a spherical reservoir, and the electrodes are embedded on the reservoir surface such that the resultant local electric body forces mix the fiuid. The electric field and electric body force distributions along with the resultant velocity field at the final steady-state condition are presented. The mixing mechanism is illustrated by the time evolution of temperature distribution inside the reservoir. The effects of primary dimensionless numbers on the mixing time are studied.

Heat transfer enhancement of a Poiseuille flow by means of electric conduction phenomenon

Electrohydrodynamic (EHD) conduction phenomenon involves the interaction of electric field and flow field in a dielectric fluid medium via the process of dissociation and recombination of free charges. This paper numerically studies the effect of electric conduction phenomenon on the heat transfer characteristics of a Poiseuille flow. The numerical domain consists of six electrode pairs positioned along the tube wall. The flow is primarily generated by an external pressure-gradient imposed along the tube. The electric field and electric body force distributions and the resultant velocity fields are presented. The heat transfer enhancements are illustrated under various operating conditions.

A high-fidelity approach towards simulation of pool boiling

A novel numerical approach is developed to simulate the multiscale problem of pool-boiling phase change. The particular focus is to develop a simulation technique that is capable of predicting the heat transfer and hydrodynamic characteristics of nucleate boiling and the transition to critical heat flux on surfaces of arbitrary shape and roughness distribution addressing a critical need to design enhanced boiling heat transfer surfaces. The macro-scale of the phase change and bubble dynamics is addressed through employing off-the-shelf Computational Fluid Dynamics (CFD) methods for interface tracking and interphase mass and energy transfer. The micro-scale of the microlayer, which forms at early stage of bubble nucleation near the wall, is resolved through asymptotic approximation of the thin-film theory which provides a closed-form solution for the distribution of the micro-layer and its influence on the evaporation process. In addition, the sub-grid surface roughness is represented stochastically throug...

An Electrically Driven Impinging Liquid Jet for Direct Cooling of Heated Surfaces

An electrically driven impinging liquid jet concept is being proposed and numerically investigated for direct cooling of heated surfaces. The liquid jet flow is generated with the aid of uniquely designed electrodes immersed in a liquid bath and positioned nearby a heated surface. The jet flow is generated based on the electric conduction phenomenon. This numerical study reveals that high impinging jet velocities can be generated with the proposed electrode design, allowing for the effective removal of the heat from the heated surfaces.

Thermal Homogenization in Spherical Reservoir by EHD Conduction Phenomenon

Electrohydrodynamic (EHD) conduction phenomenon involves the interaction of electric field and flow field in a dielectric fluid medium via the process of dissociation and recombination of free charges. This paper numerically studies the effect of electric conduction phenomenon on the mixing mechanism of two fluids with identical physical properties but separated due to the non-homogeneity of the temperature field. The fluid is designated to be restored in a spherical reservoir and it is not spontaneously mixed since the reservoir is predicted to be located in non-gravity environment. The electrodes are embedded on the reservoir surface such that the resultant electric body force causes the fluid with higher temperature mixes with the colder fluid and vice versa. The electric field and electric body force distribution and the resultant velocity field are presented. The results are illustrated in the form of time evolution of temperature distribution inside the reservoir. The effects of primary dimensionless numbers on the mixing time are studied.Copyright

Enhancement of External Condensation Heat Transfer by Pumping of Liquid Condensate Circumferentially With Electric Conduction Phenomenon

Electrohydrodynamic (EHD) conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes, generated by the process of dissociation of the neutral electrolytic species and recombination of the generated ions. This paper numerically investigates the effect of EHD conduction pumping of liquid condensate circumferentially on the heat transfer performance of a condensation tube. The local interface profile is determined by the balance of fluid velocity and inter-phase momentum exchange. The conduction mechanism is designated to pump the liquid film from the top portion of the tube where the gravity body force plays minimal role. The interface profile, liquid condensate flow structure, and heat transfer rate under operating of one electrode pair and two electrodes pairs are investigated. The heat transfer performance for various operating conditions is also studied in this paper.Copyright

Numerical Investigation of EHD Conduction Pumping of Liquid Film With Phase-Change

Electrohydrodynamic (EHD) conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes, generated by the process of dissociation of the neutral electrolytic species and recombination of the generated ions. This paper numerically investigates the EHD conduction pumping of a thin liquid film in the presence of phase change. The flow system comprises a liquid film flowing over a two-dimensional flat plate while the vapor phase extended far beyond the interface to result in almost motionless vapor. The channel is separated into four different sections: the entrance, electrode, evaporation, and downstream sections. The entrance, electrode and downstream regions are adiabatic while a constant heat flux is applied in the evaporation side. The concept of EHD conduction pumping of liquid film in the presence of phase change is demonstrated in this paper. The enhanced heat transfer due to conduction pumping is evaluated.Copyright