HR: 17:50h
AN: NG14A-08    [Abstracts]
TI: Entropy Budgets in Oscillating and Freezing Systems
AU: * Lorenz, R D
EM: rlorenz@lpl.arizona.edu
AF: Lunar and Planetary Lab, University of Arizona, 1629 E. University Blvd, Tucson, AZ 85721 United States
AB: An interesting spontaneously oscillating system was demonstrated some decades ago by Welander : an open-topped water tank supplied with a continuous supply of heat is exposed to chilled air. A layer of ice forms, as one might expect. However, the ice retards the loss of heat to the air, and the water temperature rises until eventually the ice melts. The enhanced heat loss allows the system to cool again to the point where ice can form, and the cycle repeats. The oscillating behaviour is counterintuitive (like another freezing phenomenon, the Mpemba effect, wherein a warm liquid will begin freezing before a cool one), but is in full accord with the laws of thermodynamics and can be demonstrated in the laboratory and with numerical models. Oscillations occur in specific regions of parameter space (heating rate, heat transfer coefficients etc) - smooth variation, e.g. of the ice:air heat transfer coefficient yields a smooth variation of entropy production, except for a jump to increased entropy production when oscillations begin. A geophysical system where similar oscillations may occur is the icy Jovian satellite Europa, which appears to have a young crust. More generally, where a system is subject to a varying excitation (such as diurnal or seasonal forcing of the climate of Earth or Mars) the presence of phase changes such as melting of water or the condensation of carbon dioxide as frost have an important impact on the entropy budget of the system.
DE: 0748 Ponds
DE: 0766 Thermodynamics (1011, 3611, 8411)
DE: 4435 Emergent phenomena
DE: 6221 Europa
DE: 6225 Mars
SC: Nonlinear Geophysics [NG]
MN: Fall Meeting 2005