Modern problems of electroconvective heat and masstransfer
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GROSU, Fiodor, BOLOGA, M.. Modern problems of electroconvective heat and masstransfer. In: Materials Science and Condensed Matter Physics, Ed. 6, 11-14 septembrie 2012, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2012, Editia 6, p. 261. ISBN 978-9975-66-290-1.
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Materials Science and Condensed Matter Physics
Editia 6, 2012
Conferința "Materials Science and Condensed Matter Physics"
6, Chișinău, Moldova, 11-14 septembrie 2012

Modern problems of electroconvective heat and masstransfer


Pag. 261-261

Grosu Fiodor, Bologa M.
 
Institute of Applied Physics
 
Disponibil în IBN: 25 martie 2020


Rezumat

Problems of heat and mass transfer comprise broad areas of scientific and technological activities and are an integral part of numerous technologies and processes. We consider a special case of those problems, namely, electroconvective (EC) heat and mass transfer (HMT). Unlike the classical HMT, the driving forces of EC HMT are ponderomotive forces of electrical nature. Taking into account that in the problems of natural convection, the acceleration due to gravity is constant while in the problems of electric convection, the spatial distribution of the electric field intensity is a variable quantity, it becomes clear that electroconvective heat and mass transfer phenomena are much more complicated. There are many cases where problems admit solutions, including the analytical ones, some of such problems are considered in this report. The problems of EC HMT form a subdomain of scientific area, electrohydrodynamics (EHD), which studies the interaction of electric fields and dielectric fluids. One of the main problems is the electrification of media. The solution of this problem lies in the possible existence in the liquids, especially in an electric field, of polycrystalline structures with sizes in the nano-range.Another problem is related to the mathematical difficulties in solving the complex equations of EHD, which includes the set of equations of electrodynamics (Maxwell’s equations), hydrodynamics (the Navier-Stokes equations), heat and mass transfer (such as Fourier and Fick’s equations, etc.) and are being successfully overcome by numerical and graphical methods. However, analytical, even approximate solutions of problems, are very valuable, because they are transparent from a physical point of view. The use of innovative approaches in research and new progressive technologies allows overcoming the practical problems. Concerning practical aspects, we can note that the development of electrohydrodynamics is much connected with the effect of the intensification of heat transfer in the dielectric liquids under the influence of the electric field due to electric convection (electroconvective phenomena). Professor G.A. Ostroumov was the first to formulate the most complete system of equations of electric convection, based on which its main regularities and characteristics were determined.Problems of heat transfer have been studied systemically in the Institute of Applied Physics,Academy of Sciences of Moldova. Electroconvective heat transfer in homogeneous and heterogeneous media (emulsions, suspensions), at phase transitions (boiling and condensation), in aerosol and other dispersed systems have been studied. Dimensionless dependencies, confirmed by numerous experimental results, have been found. As far as mass transfer is concerned, the electrical purification of liquids has been thoroughly investigated. The essence of purification consists in particles charging with their subsequent removal. The main problem of electroconvective mass transfer is the electrification of both continuous and dispersed phases. The problem of the distribution of the concentration of the dispersed phase is solved analytically, by splitting the space of electroprecipitator into the emitter region (charging of dispersions) and the collector region (capture and retaining of particles). As soon as the gradients of concentration of particles in both regions are very small, it is expected that their transfer takes place due to the Coulomb forces. At the interface between two regions exists almost abrupt change in concentration and the mass transfer is controlled by diffusion and is analyzed based on the theory of the boundary layer. Heat and mass transfer are associated with a large variety of physically interesting processes, including those connected with electrohydrodynamic pumping of liquids, EHD power generation, as well as with the phenomena associated with electrotransfer in the clouds, especially in a storm. All these phenomena and processes are on the stage of in-depth research and innovative developments, as well as possible practical applications.