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CNAA / Theses / 2009 / June /

Thermoelectroconvective phenomena and their applied aspects


Author: Grosu Feodor
Degree:doctor habilitat of engineering
Speciality: 05.14.05 - Heat engineering theory
Year:2009
Scientific consultant: Mircea Bologa
doctor habilitat, professor, Institute of Applied Physics of the
Institution:
Scientific council:

Status

The thesis was presented on the 11 June, 2009
Approved by NCAA on the 1 October, 2009

Abstract

Adobe PDF document – 1.10 Mb / in russian
Adobe PDF document – 1.17 Mb / in romanian

Summary

The thesis is dedicated to the investigation of the phenomena of interaction of electric fields with perfect or low-conducting liquid dielectric media, comparatively new sphere of physics – electric hydrodynamics (EHD) or narrower thermoelectric hydrodynamics (TEHD) in the case of thermally non-uniform media.

The aim of the research is the study of EHD phenomena and reveal of their applied aspects conformably to the solution of some urgent physicotechnical problems: control of the processes of transfer of heat, mass and charge; energy transformation; separation of heterogeneous systems (filtration); the search of new (alternate) energy sources.

Hydrodynamic effects of EHD interactions appear as macroscopic motion of the liquid under the influence of external electric fields called electric convection (EC). To investigate it the media are divided into two classes: perfect dielectrics from the point of view of the conductivity being zero and low-conducting ones when this parameter is small but not zero. It is shown that oned of the necessary conditions of the origin and existence of electroconvective phenomena is heterogeneity of the medium with respect to its electrophysical parameters (ε and/or σ), owing to the following inhomogeneities: thermal, mechanical (heterogeneous media – emulsions, suspensions) and caused by the electric field itself.

It has been realized the classification of EHD phenomena: thermoelectroconvective ones, such as electrothermal convection (ETC) in perfect (ETCP) and low-conducting (ETCL) liquids, as well as ETC caused by joule heating (ETCJ); mechanoelectroconvective ones in heterogeneous media (electromechanical convection, EMC); electroconvective phenomena in homogeneous isothermal gases and liquids typical for greatly non-uniform fields and known under the name of the electric wind (EW), and in the case of the uniform and weakly non-uniform external fields they are called electroisothermal convection (EITC). Much attention is given to the thermoelectroconvective phenomena as they are the most important from the standpoint of the applied aspects of EHD phenomena.

Equilibrium hydrostatic state and all types of electroconvective phenomena; convective instability; laminar convection; the developed convection intensity; one-dimensional flows have been studied.

Electrophysical parameters of disperse media are found and EMC regularities are examined in detail. In the case of isothermal phenomena there have been analyzed different mechanisms of electrization of liquids and almost all experimentally known types of charge generation have been explained. Proper distributions of electric field and charges are obtained. A number of problems on isothermal flows and regularities of charge relaxation in them interesting not only from theoretical point of view but practical as well have been solved. The notion of the “electric” Reynolds number (the main qualitative and quantitative characteristic of EHD phenomena) is introduced.

The regularities of electroconvective heat exchange are revealed and generalized criterial equations for the Nusselt number for all cases of convections ETCP; ETCL; ETCJ; EMC (emulsions, suspensions); EW (at various pressures); EITC are found.

The physical aspects of energy transformation methods : electric power into mechanical one (EHD pumps and inversely - mechanical energy into electric one (EHD generators) are examined and discussed. The procedure of transformation efficiency calculation is presented.

The computation of the wind EHD generator and isothermal EHD “flowmeter-generator” are presented. Much attention is given to TEHD methods of transformation as the case in point is the transformation of namely heat energy into other types being the priority problem. The found solutions of some problems are recommended as physical models of TEHD pumps in the case of perfect dielectrics or/and TEHD generators in low-conducting media. Formulas for liquids flows and current densities are obtained. The currents at one-dimensional isothermal flows and one-dimensional convection of wet air in the inclined capacitor simulating the natural convection on the hillside in the thundery weather, i.e. under the conditions of the electrified air, have been calculated.

Another target of investigation is the problem of filtration of dielectric low-conducting heterogeneous liquid systems, in the first place with the aim of their electric refinement. The foundation of electric filtration theory has been created and the mathematical simulation of the process in the form of composite-exponential function being the basis of the data treatment and generalization.

The laboratory simulation of the atmosphere moisture circulation has been carried out in order to examine the possibilities to get electric power and water from the atmosphere and soil. Encouraging results have been received which should be thoroughly analyzed. General conclusions and practical recommendations are presented.