Fluid Dynamics Seminar

Monday, April 17th, 2006, 11:30 AM
Cullimore Lecture Hall, Room 611
New Jersey Institute of Technology


Entropy extraction rate and a test for fluctuation relation in compressible turbulence

Mahesh M. Bandi


Department of Physics and Astronomy, University of Pittsburgh



Fluctuations at equilibrium being tiny, statistical averages carry a clear meaning for such systems, providing easy characterization of temperature and entropy. When energy is injected into a system it is driven out of thermal equilibrium. Such energy has to eventually dissipate into heat for the system to relax back into equilibrium. Such systems exhibit long range correlations in space and time, thus resulting in wild fluctuations. It becomes difficult therefore, to ascribe a meaningful temperature or entropy to nonequilibrium processes. However, since dissipation corresponds to an increase in entropy, understanding the evolution of temperature or entropy becomes imperative. In a nonequilibrium steady state the rate at which the system loses entropy to the environment (entropy extraction rate) naturally attains a constant value. Indeed, recent theory suggests that the entropy extraction rate plays a more meaningful role in nonequilibrium processes than the entropy itself. We experimentally measure the entropy extraction rate for a system of particles floating on the surface of a tank of water maintained in turbulent steady state and compare our results with existing theory.