Preface

E. Blūms - A. Cēbers

Institute of Physics, University of Latvia Salaspils, Latvia

Abstract
During the last decades exciting scientific results and applied achievements have been obtained in the field of magnetic fluids. Starting as an interesting interdisciplinary research area of physics, chemistry and hydrodynamics and owing to serious technological developments the ferrofluids have got a practical implementation as important materials of wide engineering and technological application. The journal "Magnetohydrodynamics" has been paying attention to the magnetic fluids since the early 70's when intensive research in ferrofluid dynamics started. Already in the first period, besides physical and hydrodynamic problems, the attention of researchers had been focused on the thermodynamic characteristics and heat and mass transfer properties of colloids under the action of a magnetic field. New phenomena such as thermo- and solute magnetic convection, magnetophoresis of colloidal particles and their high gradient magnetic separation, magnetically and thermally induced phase transition in colloids as well as some other macroscopic and microscopic properties of ferrofluids were considered and discussed. Recently, employing new sensitive measurement techniques -- an optically induced thermal grating in thin layers and convective separation in non-isothermal shear flows -- unusually high thermophoretic mobility of colloidal ferroparticles has been registered. The non-uniformity of the fluid magnetization due to temperature and concentration gradients reasons the dependence of the transport properties of colloid on the magnetic field; the interaction of thermal and Soret-driven solutal buoyancy is a reason of specific double-diffusive magnetoconvective instabilities' development. External factors (radiation, electromagnetic field, etc.) evoke some additional specific changes in the heat and mass transfer properties. Besides the scientific interest, some of these phenomena should be taken into account also in the ferrofluid applications. To attract the attention of readers to new research problems, we proposed to publish a special Issue of the Journal on heat and mass transfer. Many colleagues followed our invitation and submitted a number of review articles and contributed papers. Of course, it was not possible to reflect all the new ideas and results, some of them have to be investigated more thoroughly and precisely. Nevertheless, we hope that the Issue will arise an interest of readers and stipulate their new research activities.