The Mpemba effect is the name given to the assertion that it is quicker to cool water to a given temperature when the initial temperature is higher. This assertion seems counter-intuitive and yet references to the effect go back at least to the writings of Aristotle. Indeed, at first thought one might consider the effect to breach fundamental thermodynamic laws, but we show that this is not the case. We go on to examine the available evidence for the Mpemba effect and carry out our own experiments by cooling water in carefully controlled conditions. We conclude, somewhat sadly, that there is no evidence to support meaningful observations of the Mpemba effect.
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http://dx.doi.org/10.1038/srep37665 | DOI Listing |
Sci Rep
November 2016
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA, UK.
ACS Macro Lett
January 2016
Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Strasse 6, 01069 Dresden, Germany.
Using molecular dynamics simulations and primitive path analysis, we show that hot entangled polymer melts can crystallize faster with higher crystallinities and larger crystalline stem lengths, as compared to cold melts under rapid quenching conditions or during cold-crystallization. This counterintuitive phenomenon similar to the so-called Mpemba effect observed for water can be explained by the temperature dependence of entanglements. Our results demonstrate the key role of the entanglement state for crystallization properties and provide a new approach to understand the role of thermal history and to the open question of thickness selection in polymer crystallization.
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