Mpemba effect
Encyclopedia
The Mpemba effect is the observation that warmer water sometimes freezes faster than colder water. Although the observation has been verified, there is no single scientific explanation for the effect.
, and early modern scientists such as Francis Bacon
and René Descartes
. Aristotle's explanation involved an erroneous 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".
n Erasto Mpemba
. He first encountered the phenomenon in 1963 in Form 3 of Magamba Secondary School, Tanganyika
when freezing ice cream
mix that was hot in cookery classes and noticing that they froze before cold mixes. After passing his O-level examinations, he became a student at Mkwawa Secondary (formerly High) School, Iringa
, Tanzania
. The headmaster invited Dr. Denis G. Osborne from the University College in Dar Es Salaam
to give a lecture on physics
. After the lecture, Erasto Mpemba asked him the question "If you take two similar containers with equal volumes of water, one at 35 °C (95 °F) and the other at 100 °C (212 °F), and put them into a freezer, the one that started at 100 °C (212 °F) freezes first. Why?" only to be ridiculed by his classmates and teacher. After initial consternation, Dr. Osborne experimented on the issue back at his workplace and confirmed Erasto's finding. They published the results together in 1969.
. Blocking heat transfer from the top with a film of oil drastically slowed cooling. Also, the effect of dissolved air was accounted for by using boiled water. The beakers were also insulated from the bottom.
At first sight, the behaviour seems contrary to thermodynamics
. Many standard physical theory effects contribute to the phenomenon, although no single explanation is conclusive. Several effects may contribute to the observation, depending on the experimental set-up:
(CFD) is notoriously difficult."
This effect is a heat transfer problem, and 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.
writes, "Even if the Mpemba effect is real — if hot water can sometimes freeze more quickly than cold — it is not clear whether the explanation would be trivial or illuminating." He pointed out that investigations of the phenomenon need to control a large number of initial parameters (including type and initial temperature of the water, dissolved gas and other impurities, and size, shape and material of the container, and temperature of the refrigerator) and need to settle on a particular method of establishing the time of freezing, all of which might affect the presence or absence of the Mpemba effect. The required vast multidimensional array of experiments might explain why the effect is not yet understood.
New Scientist
recommends starting the experiment with containers at 35 °C (95 °F) and 5 °C (41 °F) to maximize the effect.
Historical observations
Similar behavior was observed by ancient scientists such as AristotleAristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...
, and early modern scientists such as Francis Bacon
Francis Bacon
Francis Bacon, 1st Viscount St Albans, KC was an English philosopher, statesman, scientist, lawyer, jurist, author and pioneer of the scientific method. He served both as Attorney General and Lord Chancellor of England...
and René Descartes
René Descartes
René Descartes ; was a French philosopher and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day...
. Aristotle's explanation involved an erroneous property he called antiperistasis
Antiperistasis
Antiperistasis, in philosophy, is a general term for various processes, real or contrived, in which one quality heightens the force of another, opposing, quality...
, defined as "the supposed increase in the intensity of a quality as a result of being surrounded by its contrary quality".
Origin
The effect is named after TanzaniaTanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
n Erasto Mpemba
Erasto Mpemba
Erasto Barthlomeo Mpemba is a Tanzanian scientist who observed what became known as the Mpemba effect, whereby hot water sometimes freezes faster than cold water. This effect had been observed previously by Aristotle, Francis Bacon, and René Descartes.Mpemba made the discovery at the age of about...
. He first encountered the phenomenon in 1963 in Form 3 of Magamba Secondary School, Tanganyika
Tanganyika
Tanganyika , later formally the Republic of Tanganyika, was a sovereign state in East Africa from 1961 to 1964. It was situated between the Indian Ocean and the African Great Lakes of Lake Victoria, Lake Malawi and Lake Tanganyika...
when freezing ice cream
Ice cream
Ice cream is a frozen dessert usually made from dairy products, such as milk and cream, and often combined with fruits or other ingredients and flavours. Most varieties contain sugar, although some are made with other sweeteners...
mix that was hot in cookery classes and noticing that they froze before cold mixes. After passing his O-level examinations, he became a student at Mkwawa Secondary (formerly High) School, Iringa
Iringa
Iringa is a city in Tanzania with a population of 112,900 . It is situated at a latitude of 7.77°S and longitude of 35.69°E. The name is derived from the Hehe word lilinga, meaning fort....
, Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
. The headmaster invited Dr. Denis G. Osborne from the University College in Dar Es Salaam
Dar es Salaam
Dar es Salaam , formerly Mzizima, is the largest city in Tanzania. It is also the country's richest city and a regionally important economic centre. Dar es Salaam is actually an administrative province within Tanzania, and consists of three local government areas or administrative districts: ...
to give a lecture on physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
. After the lecture, Erasto Mpemba asked him the question "If you take two similar containers with equal volumes of water, one at 35 °C (95 °F) and the other at 100 °C (212 °F), and put them into a freezer, the one that started at 100 °C (212 °F) freezes first. Why?" only to be ridiculed by his classmates and teacher. After initial consternation, Dr. Osborne experimented on the issue back at his workplace and confirmed Erasto's finding. They published the results together in 1969.
Causes
Osborne observed that the top is warmer than the bottom in a beaker of water being cooled, the difference being sustained by convectionConvection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. Blocking heat transfer from the top with a film of oil drastically slowed cooling. Also, the effect of dissolved air was accounted for by using boiled water. The beakers were also insulated from the bottom.
At first sight, the behaviour seems contrary to thermodynamics
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
. Many standard physical theory effects contribute to the phenomenon, although no single explanation is conclusive. Several effects may contribute to the observation, depending on the experimental set-up:
- Definition of frozenFreezingFreezing or solidification is a phase change in which a liquid turns into a solid when its temperature is lowered below its freezing point. The reverse process is melting....
: 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? Some experiments have instead measured the time until the water reached 0°C. - EvaporationEvaporationEvaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
: The evaporation of the warmer water reduces the mass of the water to be frozen. Evaporation is endothermicEndothermicIn thermodynamics, the word endothermic describes a process or reaction in which the system absorbs energy from the surroundings in the form of heat. Its etymology stems from the prefix endo- and the Greek word thermasi,...
, meaning that the water mass is cooled by vapor carrying away the heat, but this alone probably does not account for the entirety of the effect. - ConvectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
: Accelerating heat transferHeat transferHeat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...
s. Reduction of water density below 4 °C (39.2 °F) tends to suppress the convection currents that cool the lower part of the liquid mass; the lower density of hot water would reduce this effect, perhaps sustaining the more rapid initial cooling. Higher convection in the warmer water may also spread ice crystals around faster. - FrostFrostFrost is the solid deposition of water vapor from saturated air. It is formed when solid surfaces are cooled to below the dew point of the adjacent air as well as below the freezing point of water. Frost crystals' size differ depending on time and water vapour available. Frost is also usually...
: Has insulatingThermal insulationThermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
effects. The lower temperature water will tend to freeze from the top, reducing further heat loss by radiation and air convection, while the warmer water will tend to freeze from the bottom and sides because of water convection. This is disputed as there are experiments that account for this factor. - SupercoolingSupercoolingSupercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid....
: It is hypothesizedHypothesisA hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
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 to be less significant where there are particles that act as nuclei for ice crystals, thus precipitating rapid freezing. - SolutesSolutionIn chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
: The effects of calciumCalcium carbonateCalcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
, magnesium carbonateMagnesium carbonateMagnesium carbonate, MgCO3, is a white solid that occurs in nature as a mineral. Several hydrated and basic forms of magnesium carbonate also exist as minerals...
among others. - The effect of heating on dissolvedSolvationSolvation, also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute...
gasGasGas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
es; however, this was accounted for in the original article by using boiled water.
Scalar functionality
According to an article by Monwhea Jeng: "Analysis of the situation is now quite complex, since we are no longer considering a single parameter, but a scalar function, and computational fluid dynamicsComputational fluid dynamics
Computational fluid dynamics, usually abbreviated as CFD, is a branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. Computers are used to perform the calculations required to simulate the interaction of liquids and gases with...
(CFD) is notoriously difficult."
This effect is a heat transfer problem, and therefore well suited to be studied from a transport phenomena
Transport phenomena (engineering & physics)
In engineering and physics, the study of transport phenomena concerns the exchange of mass, energy, or momentum between observed and studied engineering systems. This subject is a fundamental component of disciplines involved with fluid mechanics, heat transfer, and mass transfer...
viewpoint, based on continuum mechanics
Continuum mechanics
Continuum mechanics is a branch of mechanics that deals with the analysis of the kinematics and the mechanical behavior of materials modelled as a continuous mass rather than as discrete particles...
. 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.
Recent view of the Mpemba effect
A reviewer for Physics WorldPhysics World
Physics World is the membership magazine of the Institute of Physics, one of the largest physical societies in the world. It is an international monthly magazine covering all areas of physics, both pure and applied, and is aimed at physicists in research, industry and education worldwide...
writes, "Even if the Mpemba effect is real — if hot water can sometimes freeze more quickly than cold — it is not clear whether the explanation would be trivial or illuminating." He pointed out that investigations of the phenomenon need to control a large number of initial parameters (including type and initial temperature of the water, dissolved gas and other impurities, and size, shape and material of the container, and temperature of the refrigerator) and need to settle on a particular method of establishing the time of freezing, all of which might affect the presence or absence of the Mpemba effect. The required vast multidimensional array of experiments might explain why the effect is not yet understood.
New Scientist
New Scientist
New Scientist is a weekly non-peer-reviewed English-language international science magazine, which since 1996 has also run a website, covering recent developments in science and technology for a general audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of...
recommends starting the experiment with containers at 35 °C (95 °F) and 5 °C (41 °F) to maximize the effect.
See also
- Leidenfrost effectLeidenfrost effectThe Leidenfrost effect is a phenomenon in which a liquid, in near contact with a mass significantly hotter than the liquid's boiling point, produces an insulating vapor layer which keeps that liquid from boiling rapidly...
– lower temperature boilers can vaporize water faster than higher temperature boilers - Arrhenius equationArrhenius equationThe Arrhenius equation is a simple, but remarkably accurate, formula for the temperature dependence of the reaction rate constant, and therefore, rate of a chemical reaction. The equation was first proposed by the Dutch chemist J. H. van 't Hoff in 1884; five years later in 1889, the Swedish...
– chemical reactions happen faster at higher temperatures
External links
- http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&db_key=PRE&sim_query=YES&aut_xct=NO&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=&txt_logic=OR&text=Mpemba+&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1assabs.harvard.edu] article collection. - History and analysis of the Mpemba Effect. in the University of CaliforniaUniversity of CaliforniaThe University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
Usenet Physics FAQ An analysis of the Mpemba effect. London South Bank UniversityLondon South Bank UniversityLondon South Bank University is a university in south London. With over 25,000 students and 1,700 staff, it is based in the London Borough of Southwark, near the South Bank of the River Thames, from which it takes its name...
. A possible explanation of the Mpemba Effect