Savako Nakamae

Thermoelectric diffusion in ferrofluids: Possible application of complex fluids in waste-heat recovery

Par Sawako Nakamae, SPEC/IRAMIS/DRF/CEA, Saclay, France

Mardi 15 Mars, 14h, Salle des séminaires, 3ème étage, Batiment A4

Abstract :

In simplest terms, thermopower describes the material’s property where an electric voltage ∆V, is induced by the application of a temperature difference ΔT across its body: ∆V=-Se ∆T, where Se is the Seebeck coefficient. The great majority of today’s thermoelectric (TE) research is focused on improving the efficiency of solid-state TE materials via nanostructuring; which presents a substantial production cost. A cheaper and simpler alternative to convert low temperature waste heat into electrical energy can be found in “liquid thermocells” using complex fluids such as ferrofluids. In ferrofluids, Se is coupled to the movement of charged ionic species (macro-ions, nanoparticles, etc.) and thus it is closely related to the “Soret effect,” i.e., the thermal diffusion of nanoparticles.
At SPEC/CEA-Saclay, we are investigating the thermopower of ionically stabilized ferrofluids made of maghemite nanoparticles dispersed in various non-magnetic liquid media (e.g., dimethyl sulfoxide, water and ionic liquids) under a temperature gradient. The thermopower is measured as a function of nanoparticle concentration and the results are compared to the corresponding Soret coefficients determined via Forced Rayleigh scattering technique (by PHENIX/UPMC). We interpret the connection between the thermoelectric and thermodiffusion effects in terms of a common parameter, the Eastman entropy of transfer of nanoparticles. The values of the Eastman entropy of transfer obtained from both experiments are a few orders of magnitude larger than typical electrolyte ions and are in a quantitative agreement, lending support to the existing theoretical models. Simultaneously, our findings open a new research and technological path for ferrofluids, and other complex fluids in thermoelectric device applications.
With time permitting, I will also discuss other examples of thermoelectric complex fluids currently studied in our group.