The Mpemba effect is the observation that, in some specific, fairly common circumstances, hotter water freezes faster than colder water. Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ...

The effect is named for the Tanzanian high-school student Erasto B. Mpemba. Mpemba first encountered the phenomenon in the classroom of Eugene Marschall at Mkwawa Secondary (formerly High) School, Iringa, Tanzania, where Mpemba was a student. Eugene Marschall, a member of the Teachers for East Africa/TEA program, taught chemistry and physics at this school from 1965 to 1967. Mpemba first noticed the effect in 1963 after his account of the freezing of hot ice cream mix in cookery classes, and went on to publish experimental results with Dr. Denis G. Osborne in 1969. For other uses, see High school (disambiguation). ... Hilltop view over Iringa town. ... For other uses, see Chemistry (disambiguation). ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... Missing image Ice cream is often served on a stick Boxes of ice cream are often found in stores in a display freezer. ...

At first sight, the behaviour seems contrary to thermodynamics. However, most thermodynamicists believe that each observation of the Mpemba effect can be explained with standard physical theory. Many effects can contribute to the observation, depending on the experimental set-up: Thermodynamics (from the Greek θερμη, therme, meaning heat and δυναμις, dynamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ...

• Different definition of freezing (Is it the physical definition of the point at which water forms a visible surface layer of ice, or the point at which the entire volume of water becomes a solid block of ice?)
• Evaporation, reducing the volume to be frozen. Evaporation is endothermic.
• Convection, accelerating heat transfers. Reduction of water density below 4°C tends to suppress the convection currents cooling the lower part of the liquid mass; the lower density of hot water would reduce this effect, perhaps sustaining the more rapid initial cooling.
• The insulating effects of frost
• The effect of boiling on dissolved gases
• Supercooling. It is hypothesized that cold water, when placed in a freezing environment, supercools more than hot water in the same environment, thus solidifying slower than hot water. However, supercooling tends not to be significant where there are particles, which act as nuclei for ice crystals, thus precipitating rapid freezing.
• The effect of solutes such as calcium and magnesium carbonate.

According to an article by Monwhea Jeng, there is no unique explanation yet for why, in some specific circumstances, hotter water freezes faster than colder water. The article makes no attempt to focus on the relevant transport phenomena concepts such as temperature and fluid flow fields. Indeed when temperature fields are introduced, the author states: “Vaporization” redirects here. ... Convection in the most general terms refers to the internal movement of currents within fluids (i. ... Thermal insulation on the Huygens probe The term thermal insulation can refer to materials used to reduce the rate of heat transfer, or the methods and processes used to reduce heat transfer. ... Frost on black pipes Frost is a solid deposition of water vapor from saturated air. ... Italic text This article is about the boiling point of liquids. ... For the connotation of the term relating to chemistry, see Solvation. ... For other uses, see Gas (disambiguation). ... Supercooling is the process of chilling a liquid below its freezing point, without it becoming solid. ... Look up Hypothesis in Wiktionary, the free dictionary. ... A substance is soluble in a fluid if it dissolves in the fluid. ... Calcium carbonate is a chemical compound, with the chemical formula CaCO3. ... Magnesium carbonate, MgCO3, is a white solid that occurs in nature as a mineral. ...

Analysis of the situation is now quite complex, since we are no longer considering a single parameter, but a scalar function, and computational fluid dynamics (CFD) is notoriously difficult. The greatest difficulties with CFD are with turbulent flow; with laminar (streamline) flow, as we have in this case, there is much better consistency between independent analyses, and a CFD analysis could be expected to be illuminating.

This effect is a heat transfer problem, therefore well suited to be studied from a transport phenomena viewpoint, based on continuum mechanics. When heat transfer is analyzed in terms of partial differential equations, whose solutions depend on a number of conditions, it becomes clear that measuring only a few lumped parameters, such as the water average temperature is generally insufficient to define the system behaviour, since conditions such as geometry, fluid properties and temperature and flow fields play an important role. The counterintuitiveness of the effect, if analyzed only in terms of simplified thermodynamics illustrates the need to include all the relevant variables and use the best available theoretical tools when approaching a physical problem. The first edition of Transport Phenomena was published in 1960, two years after having been preliminarily published under the title Notes on Transport Phenomena based on mimeographed notes prepared for a chemical engineering course taught at the University of Wisconsin during the academic year 1957-1958. ... Continuum mechanics is a branch of physics (specifically mechanics) that deals with continuous matter, including both solids and fluids (i. ... In mathematics, and in particular analysis, a partial differential equation (PDE) is an equation involving partial derivatives of an unknown function. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...

Similar behavior may have been observed by ancient scientists such as Aristotle, and Early Modern scientists such as Francis Bacon and René Descartes. Aristotle's explanation involved a physical property he called antiperistasis, defined as "the supposed increase in the intensity of a quality as a result of being surrounded by its contrary quality". He used the concept of antiperistasis to provide evidence for his conjecture that human bodies and bodies of water were hotter in the winter than in the summer, a theory that was later disproved by Medieval and Renaissance observations. Aristotle (Greek: AristotélÄ“s) (384 BC – 322 BC) was a Greek philosopher, a student of Plato and teacher of Alexander the Great. ... The early modern period is a term used by historians to refer to the period in Western Europe and its first colonies, between the Middle Ages and modern society. ... For other persons named Francis Bacon, see Francis Bacon (disambiguation). ... “Descartes” redirects here. ... This article is about modern humans. ... The Middle Ages formed the middle period in a traditional schematic division of European history into three ages: the classical civilization of Antiquity, the Middle Ages, and modern times. ... The Renaissance (French for rebirth, or Rinascimento in Italian), was a cultural movement in Italy (and in Europe in general) that began in the late Middle Ages, and spanned roughly the 14th through the 17th century. ...

External links and references

• Cool? - EB Mpemba, DG Osborne - Physics Education, 1969
• David Auerbach, Supercooling and the Mpemba effect: when hot water freezes quicker than cold, American Journal of Physics, 63(10), 1995. Auerbach attributes the Mpemba effect to differences in the behaviour of supercooled formerly hot water and formerly cold water.
• Can hot water freeze faster than cold water? Nov, 1998 by Monwhea Jeng (Momo), Department of Physics, University of California
• The Straight Dope: Which freezes faster, hot water or cold water? by Cecil Adams, The Straight Dope, Chicago Reader Inc.
• HyperPhysics: The Mpemba Effect
• Charles A. Knight, The MPEMBA effect: The freezing times of hot and cold water, American Journal of Physics -- May 1996 -- Volume 64, Issue 5, p. 524
• The Mpemba Effect: Hot Water Freezes before Cold
• Other citations to the Mpemba Effect.
• Monwhea Jeng, 2006. "The Mpemba effect: When can hot water freeze faster than cold?" American Journal of Physics, volume 74, number 6, page 514. preprint
• Why water freezes faster after heating (New Scientist)

The American Journal of Physics is a peer-reviewed scientific journal published by the American Association of Physics Teachers devoted to the educational and cultural aspects of physics. ...

Bibliography

• Ball, P. (2006) "Does hot water freeze first?", Physics World, 19(4), April, 19-21