I. V. Kozhevnikov

Charge formation in liquid dielectrics under the influence of electrostatic field

Charge formation in liquid dielectrics under the influence of an electrostatic field is considered. Systematization of various types of electrization and their physical interpretations, as well as their mathematical descriptions are presented. Mechanisms of electrization, which can be subdivided into equilibrium, with and without taking into consideration diffusion currents, and nonequilibrium, with and without taking into consideration diffusion currents, are discussed. It is shown that, depending on the properties of the media, external field, and other factors, some mechanisms can be realized. Bipolar structures of the space charge are explained and the results of the numerical simulation of charge formation and current flow are given. Interrelation between media electrization and the Ohm law is considered.

Characteristics of an electrohydrodynamic pump

The head and flow rate characteristics—the dependences of the differential head and the fluid flow rate through an electrohydrodynamic pump (EHDP) on the electric field strength and the properties of the working fluid—have been derived. The head characteristics have been determined in hydrostatic and hydrodynamic modes; a linear dependence of the efficiency of the EHDP on the voltage has been found. The theoretical results are in agreement with the experimental data. Formulas for the calculation of the EHDP have been derived. It has been revealed that silicone fluid exhibits the best performance and can be used in EHD heat exchangers.

Boiling heat transfer in the field of electric forces

Comparative estimations of the vapor generation conditions on a heating surface with boiling both in the field and without it depending on the value of heat flux and the field strength are given. The pattern of the motion of the convective flows and vapor bubbles in connection with the heat transfer intensity is analyzed on the basis of high-speed filming of the boiling process.

Influence of the electric field and the arrangement of the stages on multistage pump characteristics

Results of the investigation of the influence of the geometric parameters of the gap between the stages and the galvanically isolated high voltage sources on the characteristics of a multistage electrohydrodynamic pump are presented. The optimum distance between the stages at which their mutual influence appearing due to Coulomb forces between neighboring electrodes of different stages is practically absent has been found. It is shown that similar results can be obtained under the conditions of galvanically isolated high voltage sources when the distances between the stages are comparable with the interelectrode gap in a stage. This fact will contribute to the reduction of multistage pump dimensions.

Electrohydrodynamic pump characteristics at different parameters of the interelectrode space

The possibility to improve EHD-pump characteristics by partially limiting and using the backward (cellular) flows in the interelectrode space is shown. The optimal parameters of the flow-limiting diaphragm, the accumulator, and the interelectrode space are determined.

Features of electrohydrodynamic flows in a multielectrode system

The electrohydrodynamic flow in the system “needle-two wires” has been investigated using the Shadow method with simultaneous recording of the transversal pumping intensity. An unstable electrohydrodynamic flow appears as a fluctuation of the central jet (flow from the blade) between the electrodes, which results in decreasing of the efficiency of the three-electrode system. The possibility of electrohydrodynamic flow stabilization by means of decreasing the interelectrode gap and using an additional, fourth electrode, which is situated behind the first two electrodes, is shown. A theoretical model of the pumping process considering the flow as a diffuser flow from the blade limited by two lateral eddies near the upper electrode collectors is proposed. As the electrohydrodynamic flow develops, the average speed of the diffuser flow, as well as the eddy dimensions, is increasing. These two factors influence the maximum flow rate of the electrohydrodynamic pump. The maximum flow rate was found theoretically, and the optimum parameters of the electrohydrodynamic pump were established.

The Effect of an Electric Field on Plane Wall Cooling

One of the most efficient and promising ways to intensify thermal exchange is to use electroconvection phenomena [1]. Under the effect of an external electric field, free space charges are formed in a dielectric fluid; during their motion, these charges entrain a neutral medium, intensively agitating it. In the process, electrohydrodynamic flows are formed at a certain field density; as this density increases, a transition from a laminar to a turbulized flow mode is observed. Flow velocities, depending on the electrophysical properties of the working material, can be as high as 1 m/s. As a rule, for the process to be intensified, electroconvection is used to agitate a heat carrier, which results in a decrease in the thickness of the thermal boundary layer and an increase in the coefficient of the wall heat transfer to the fluid.

Relaxation of Output Characteristics of Electrohydrodynamic Pumps

The principle of operation of an electrohydrodynamic pump (EHDP) is explained. Research problems are formulated for the study of the patterns and peculiarities of the operation of the EHDP for the purpose of its optimization. The experimental facility is described and the peculiarities of the relaxation of the output characteristics of a single-stage EHDP are determined. The dependences of the pressure and current characteristics on the time and voltage (dc) supplied to the EHDP are presented. New results related to very long operation of EHDPs are revealed, e.g., the fact that the pressure characteristics are fluctuating time functions. A theoretical model of the electric current transfer in an EHDP is presented, which is based on an analog electrical circuit.

Heat transfer of an evaporator–condensing system with electrohydrodynamic coolant circulation and different spatial orientation

The influence of the spatial orientation of an evaporator–condensing system (ECS) on the heat transfer coefficient is considered. As found, it varies according to the cosine law, which implies that it is at its minimum when the evaporator is in the top position, and it is at its maximum when the heater is in the bottom position. This is consistent with the physical considerations about the effect of buoyancy forces on heat transfer. The average velocity of coolant circulation through the ECS loop is found, and on this basis, the “electric” Reynolds number and heat transfer coefficient are estimated. The influence of pressure on heat transfer in the ECS has been analyzed. The considered phenomena have been physically interpreted; they agree well with the experimental data.

A corona-discharge dipole engine

The construction and operation of a small-sized electrostatic engine are described. It consists of a rotor in the form of a thin-walled cylinder made from a dielectric material. There are two strips of metal foil along the two diametrically opposite generatrices of the cylinder. The gap between the longitudinal edges of the strips can be varied. Similarly, two electrodes, in the form of thin rigid plates with sharp edges facing the cylinder surface, are diametrically opposed to each other and parallel to the generatrices of the cylinder. Distances from the sharp edges to the surface of the cylinder have been varied. The device is powered by a highvoltage DC source providing a symmetrical bipolar corona discharge. Experimental dependences of the engine speed on the voltage between the electrodes for different geometrical parameters are given. Regression equations are derived and presented in a graphical form. An analytic substantiation of the engine operation principle is presented, and experimental and theoretical results are discussed.