Fluctuations in nonequilibrium thermodynamics
J.V. Sengers

Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742 USA

Abstract: The lecture will deal with thermal fluctuations on hydrodynamic scales in fluids and fluid mixtures that are out of thermal or mechanical equilibrium, but in the absence of convection or turbulence. The principle of local thermodynamic equilibrium is known to be valid for the thermodynamic properties, however, it is never valid for the fluctuations of these properties. While thermal fluctuations in equilibrium fluids are spatially short ranged except at states near a critical point, fluctuations in nonequilibrium fluids are always long ranged, even far away from any hydrodynamic instability. These physical features will be demonstrated for temperature fluctuations in nonisothermal fluids, for concentration fluctuation in mixtures in the presence of a concentration gradient and for velocity fluctuations in laminar flows.