Tanzanian student Erasto Mpemba first encountered the situation while he was studying in Magamba Secondary School, in 1963. During a cookery class, he surprisingly found that a hot ice-cream mix freezes faster than a comparatively colder ice-cream mix! He and Dr. Denis Osborne investigated the matter and the phenomenon was confirmed by Dr. Osborne later. They produced a paper on the topic in 1969. Historically, it was first noted by Aristotle who explained it with a property called antiperistasis, modern science has dismissed this property of matter as an erroneous conception. Medieval scientist Francis Bacon wrote, "aqua parum tepida facilius conglacietur quam omnino frigida." It means that slightly tepid water freezes faster than very cold water. The pioneer of modern co-ordinate geometry Rene Descartes also noted this phenomenon and explained it with his theory of vortices. This theory expounds the nature of empty spaces and how it can be filled up with matter.
However, modern scientists have come up with a good number of explanations, which are dependant upon the experimental setup, dissolved air content in water, its purity, electrolytes dissolved in it and other relatable factors. Some of the most common explanations include:
1. Evaporation: Warmer water evaporates faster thus leaving a relatively smaller mass to be frozen. The endothermic nature of evaporation draws heat from the rest of the content. But this explanation is insufficient and unsatisfactory.
2. Supercooling: This hypothesis states that colder water in a low temperature environment supercools more than hot water and therefore it takes more time to solidify. But this theory does not explain the phenomenon wholly. Experiments that have utilized this theory have drawn significant differences in the conclusions. Scientist Auerbach noted supercooling near the wall in all cases during his experiment but Thomas reported no supercooling in the middle portion of the sample! The main problem is not exactly how supercooling can affect the freezing time but how supercooling is dependant upon the initial temperature. According to Dorsey's theory of phase transition, the temperature of supercooling can be affected by pre-heating. It may also vary by freezing and melting. This theory allows different portions of a bulk sample of liquid to vastly vary its supercooling properties. However, this theory allows no simple explanation to the understanding of the effect.
3. Effect of the Dissolved Solutes: This theory takes into account the effect of sodium, magnesium and other carbonate compounds and explains how these can affect the freezing properties of water.
4. Thermal Conductivity: The container of the hotter water may "melt" through a layer of frost which is an insulator. This allows the container to come in contact of a much colder layer. So, a faster process of cooling occurs. The lower temperature water will tend to freeze from the top but the hotter water will tend to freeze from the bottom.
5. Latent Heat of Condensation: The cooler container draws more condensation than the warmer container during the cooling cycle. This effectively reduces the rate of cooling. Mpemba effect is poorly understood from this theory!
According to J. D. Brownridge, "Hot water will freeze before cooler water only when the cooler water supercools, and then, only if the nucleation temperature of the cooler water is several degrees lower than that of the hot water. Heating water may lower, raise or not change the spontaneous freezing temperature." The fact that this phenomenon is not fully understood is an indication that fundamental problems lie beneath it. According to 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 dynamics (CFD) is notoriously difficult."
So, there is always a scope to do this experiment and come up with a theory that would explain this phenomenon fully and be accepted universally. Research work on this field is going on and it is expected that new theories will arise from the current concepts and would possibly include a precise mathematical modelling to account for the discrepancies in the results that have come up over the decades. Will warmer water freeze faster than colder water in the near future? Surely yes!
However, modern scientists have come up with a good number of explanations, which are dependant upon the experimental setup, dissolved air content in water, its purity, electrolytes dissolved in it and other relatable factors. Some of the most common explanations include:
1. Evaporation: Warmer water evaporates faster thus leaving a relatively smaller mass to be frozen. The endothermic nature of evaporation draws heat from the rest of the content. But this explanation is insufficient and unsatisfactory.
2. Supercooling: This hypothesis states that colder water in a low temperature environment supercools more than hot water and therefore it takes more time to solidify. But this theory does not explain the phenomenon wholly. Experiments that have utilized this theory have drawn significant differences in the conclusions. Scientist Auerbach noted supercooling near the wall in all cases during his experiment but Thomas reported no supercooling in the middle portion of the sample! The main problem is not exactly how supercooling can affect the freezing time but how supercooling is dependant upon the initial temperature. According to Dorsey's theory of phase transition, the temperature of supercooling can be affected by pre-heating. It may also vary by freezing and melting. This theory allows different portions of a bulk sample of liquid to vastly vary its supercooling properties. However, this theory allows no simple explanation to the understanding of the effect.
3. Effect of the Dissolved Solutes: This theory takes into account the effect of sodium, magnesium and other carbonate compounds and explains how these can affect the freezing properties of water.
4. Thermal Conductivity: The container of the hotter water may "melt" through a layer of frost which is an insulator. This allows the container to come in contact of a much colder layer. So, a faster process of cooling occurs. The lower temperature water will tend to freeze from the top but the hotter water will tend to freeze from the bottom.
5. Latent Heat of Condensation: The cooler container draws more condensation than the warmer container during the cooling cycle. This effectively reduces the rate of cooling. Mpemba effect is poorly understood from this theory!
According to J. D. Brownridge, "Hot water will freeze before cooler water only when the cooler water supercools, and then, only if the nucleation temperature of the cooler water is several degrees lower than that of the hot water. Heating water may lower, raise or not change the spontaneous freezing temperature." The fact that this phenomenon is not fully understood is an indication that fundamental problems lie beneath it. According to 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 dynamics (CFD) is notoriously difficult."
So, there is always a scope to do this experiment and come up with a theory that would explain this phenomenon fully and be accepted universally. Research work on this field is going on and it is expected that new theories will arise from the current concepts and would possibly include a precise mathematical modelling to account for the discrepancies in the results that have come up over the decades. Will warmer water freeze faster than colder water in the near future? Surely yes!
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