Thermophoretic separation of ultrafine particles in ferrofluids in thermaldiffusion column under the effect of an MHD convection

The aim of the paper is to evaluate the Soret coefficient S-T of colloidal particles in ferrofluids from measurements of an unsteady particle separati on in a flat thermodiffusion column. The column theory is modified taking i nto account MHD effects of thermal convection affected by a concentration b uoyancy force. It is shown that the Hartmann effect, not only in hydrocarbo n based colloids but also in ionic magnetic fluids of relatively high elect ric conductivity, does not influence significantly the particle separation dynamics. From measurements, positive values of S-T of surfacted particles in tetradecane based colloids are calculated. An anisotropy of the Soret ef fect in the presence of a uniform magnetic field is experimentally establis hed. The obtained results agree qualitatively well with the authors hydrody namic theory of particle thermomagnetophoresis. (C) 2000 Elsevier Science L td. All rights reserved.