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DY: Fachverband Dynamik und Statistische Physik

DY 40: Posters II

DY 40.8: Poster

Thursday, March 17, 2011, 17:00–19:00, P3

The Role of Convection in the Mpemba Effect — •Heiko Engelke and Jürgen Vollmer — Max Planck Institute for Dynamics and Self-Organization, 37073 Göttingen

Mpemba’s cooling effect has long been a counter-intuitive puzzle [1]: Two identical samples of liquid are kept at different temperatures, then put into the freezer. The initally hotter sample is the one that freezes first.

Research in the late 20th century indicated that evaporative cooling and supercooling of the liquid contribute to this effect [2]. Surprisingly though, the role of convection for this effect has not thoroughly been addressed so far.

To fill in this gap we explore the flow patterns: After being put into the freezer the probe starts to cool inwards from the walls, a temperature gradient builds up, and convection arises. Depending on initial parameters, we see a transition between convective and diffusive cooling. This affects the temperature distribution at the arrest of the flow, and the freezing pattern.

For various viscosities, initial temperatures and geometric configurations the evolution of the temperature and the flow field are measured. The results are compared to numerical simulations.
[1] E. Mpemba & D. Osborne, Phys Educ 4 (1969) 172.
[2] M. Jeng, Am J Phys 74 (2006) 514.