In the old good formula H 2 O, it would seem that no secrets are concluded. But in fact, water is the source of life and the most famous liquid in the world - a lot of mysteries in themselves, which sometimes not at the power to solve even scientists.
Before you 5 most interesting facts About water:
1. Hot water freezes faster cold
Take two tanks with water: in one nallem hot, and to another cold water, and put them in the freezer. Hot water will freeze faster cold, although cold water should turn into ice on the logic of things: after all, it is necessary to cool hot water to cool to the temperature cold, and then it is not necessary to cool into ice, while cold water does not need to cool. Why is it going on?
In 1963, Erasto B. Mpemba (Erasto B. MPEMBA), high school student high School In Tanzania, freezing the prepared mixture for ice cream noticed that the hot mixture was frozen in the freezer faster than cold. When the young man shared his discovery with physics teacher, he only laughed at him. Fortunately, the student was persistent and convinced the teacher to conduct an experiment, which confirmed its discovery: under certain conditions hot water It really freezes the fastest cold.
Now this phenomenon of hot water freezing faster than cold, is called "MPEMBA effect". True, for a long time, this unique property of water was noted by Aristotle, Francis Bacon and Ren Decartet.
Scientists so fully and do not understand the nature of this phenomenon, explaining it either by the difference in the supercooling, evaporation, the formation of ice, convection, or the impact of discovered gases on hot and cold water.
Note from X.Ru to the topic "Hot water freezes faster than cold."
Since the cooling issues, we, refrigerators are closer, then let themselves go into the essence of this problem and give two opinions about the nature of such a mysterious phenomenon.
1. A scientist from Washington University proposed an explanation of a mysterious phenomenon known since the times of Aristotle: why hot water freezes faster than cold.
The phenomenon that received the name of the effect of the MPEMBA is widely used in practice. For example, experts advise motorists to pour in winter in the washer tank cold, and not hot water. But what underlies this phenomenon, it remained unknown for a long time.
Dr. Jonathan Katz (Jonathan Katz) from Washington University investigated this phenomenon and came to the conclusion that an important role in it was played by dissolved substances that are deposited in water, which are deposited, reports EUREKALER.
Under dissolved substances Dr. Katz implies calcium and magnesium bicarbonates, which are contained in rigid water. When the water is heated, these substances are deposited, forming a scale on the walls of the kettle. Water that has never heated contains these impurities. As it freezes and the formation of ice crystals, the concentration of impurities in water increases 50 times. Because of this, the water freezing point is reduced. "And now water should still cool to frozen," explains Dr. Katz.
There is a second reason that prevents the freezing of non-heated water. A decrease in water freezing point reduces temperature differences between solid and liquid phases. "Because the speed with which water loses heat depends on this temperature difference, water that has not been heated, cool worse," comments Dr. Katz.
According to the scientist, its theory can be verified experimentally, because The effect of the MPEMBA becomes more noticeable for more rigid water.
2. Oxygen plus hydrogen plus cold generate ice. At first glance, this transparent substance seems very simple. In reality, the ice pays a lot of riddles. Ice, created by African Erasto Mpemba did not think about glory. Stood hot days. He wanted fruit ice. He took the packaging of juice and put it in the freezer. He made it more than once and therefore noticed that especially fast juice freezes if it was for it to hold it on the sun - to rolled it! It is strange, I thought a Tanzanian schoolchild, who arrived in the way of everyday wisdom. Does liquid turn into ice to be faster to ice, it is necessary to pre-warm it? The young man was so surprised that he shared his guess with the teacher. He reported the curiosity in print.
This story happened in the sixties of the last century. Now the "MPEMBE effect" is well known to the scientist. But for a long time, this as if a simple phenomenon remained a mystery. Why is hot water freeze faster than cold?
Only in 1996 the physicist David Auerbach found a solution. To answer this question, he spent the experiment for a whole year: heated water in the glass and cooled it again. So, what did he find out? When heated, air bubbles dissolved in water are destroyed. Water devoid of gases is easier to accompanse on the walls of the vessel. "Of course, water with a high air content will also freeze," says Auerbach, "but not at zero degrees Celsius, but only with minus four-six degrees." It is clear, waiting for longer. So, hot water freezes before cold, it is a scientific fact.
There is hardly a substance that arose before our eyes with the same ease as ice. It consists only of water molecules - that is, elementary molecules containing two hydrogen atoms and one - oxygen. However, ice, perhaps the most mysterious substance in the universe. Some of his properties scientists have never managed to explain.
2. Supercoiling and "Instant" freezing
Everyone knows that water always turns into ice when cooling to 0 ° C ... Except for some cases! Such a case, for example, is "supercoiling", which is a property of very clean water to remain liquid, even being cooled to a temperature below the freezing point. This phenomenon becomes possible due to the fact that the environment does not contain centers or crystallization cores that could provoke the formation of ice crystals. And therefore water remains in liquid form, even being cooled to a temperature below zero degrees Celsius. The crystallization process can be triggered, for example, gas bubbles, impurities (contaminants), an uneven surface of the container. Without them, water will remain in liquid state. When the crystallization process starts, you can observe how ultra-plate water is instantly turning into ice.
Look at the video (2 901 kb, 60 c) from Phil Medina (www.mrsciguy.com) and see for yourself \u003e\u003e
Comment. Highly pump water also remains liquid, even being heated to the temperature above the booster point.
3. "Glass" water
Quickly and without thinking, name how many different states have water?
If you answered three (solid, liquid, gaseous), then you are mistaken. Scientists identify at least 5 different states of water in liquid form and 14 ice states.
Remember the conversation about super-acted water? So, whatever you do, at a temperature of -38 ° C, even the cleanest ultra-plate water suddenly turns into ice. What happens with further decrease
temperatures? At -120 ° C with water, something strange begins with water: it becomes ultra-plate or dirt, as a pattern, and at temperatures below -135 ° C - turns into a "glass" or "vitreous" water - a solid in which there is no crystalline structure.
4. Quantum properties of water
At the molecular level, the water is even more surprising. In 1995, scientists conducted by scientists the neutron scattering experiment gave an unexpected result: physicists found that neutrons aimed at water molecules "see" 25% less than hydrogen protons than expected.
It turned out that at the speed of one Attestocenda (10-18 seconds) there is an unusual quantum effect, and the chemical formula of water instead of the usual one - H 2 O, becomes H 1.5 o!
5. Does water have a memory?
Homeopathy, alternative to official medicine, argues that a diluted solution of the drug may have a healing effect on the body, even if the dilution coefficient is so large that nothing else remains in the solution, except for water molecules. Proponents of homeopathy explain this paradox with the concept called "Memory of Water", according to which water at the molecular level has "memory" about the substance, once in it dissolved and retains the properties of the initial concentration solution after it does not remain any ingredient molecule.
An international group of scientists led by Professor Madeline Ennis (Queen "from the Royal University in Belfast (Queen" S University of Belfast), criticized the principles of homeopathy, in 2002 he conducted an experiment to refute this concept once and for all. The result turned out to be reverse. After What, scientists declared that they managed to prove the reality of the effect of "memory of water". However, the experiments conducted under the supervision of independent experts did not bring results. Disputes on the existence of the phenomenon of "Memory of Water" continue.
Water has many other unusual properties that we have not talked about this article.
Literature.
1. 5 Really Weird Things ABOUT WATER / http://www.neatorama.com.
2. The mystery of the water: the theory of the effect of Aristotle-Mpemba is created / http://www.o8ode.ru.
3. Non-disconnecting N.N. Secrets inanimate nature. The most mysterious substance in the universe / http://www.bibliotekar.ru.
MPEMBA effect or why hot water freeze faster than cold? The effect of the MPEMBA (Paradox of MPEMBI) is a paradox that says that hot water will freeze in some conditions faster than cold, although it must pass the temperature of the cold water during the freezing process. This paradox is an experimental fact that contradicts the usual ideas, according to which, with the same conditions, the more heated body for cooling to a certain temperature requires more time than the less heated body for cooling to the same temperature. This phenomenon was noticed at one time Aristotle, Francis Bacon and Rene Descart, but only in 1963, Tanzanian schoolboy Erassto Mpembea found that the hot mixture of ice cream freezes faster than cold. As a student of Magambaba High School in Tanzania, Erasto Mpembea did practical work on the cook case. He needed to make homemade ice cream - boil milk, dissolve sugar in it, cool it to room temperature And then put in the fridge for freezing. Apparently, MPembba was not particularly a diligent student and priedered with the fulfillment of the first part of the task. Fearing that he would not have time for the end of the lesson, he put in the refrigerator still hot milk. To his surprise, it froze even earlier than the milk of his comrades cooked according to a given technology. After that, MPEMBA experimented not only with milk, but also with ordinary water. In any case, already as a student of the Mkvava high school, he asked the question of Professor Dennis Osborne from the University College in Dar Es Salama (to read the students a lecture on physics in the university classroom: "If you take two identical containers with equal volumes of water So, in one of them, water has a temperature of 35 ° C, and in the other - 100 ° C, and put them in the freezer, then in the second water freezes faster. Why? " Osborne became interested in this issue and soon in 1969, together with Mpemba published the results of their experiments in the magazine "Physics Education". Since then, the effect discovered by them is called the effect of scam. Until now, no one knows how to explain this strange effect. Scientists have no single version, although there are many. It's all about the difference in the properties of hot and cold water, but it is not yet clear which properties play a role in this case: the difference in supercooling, evaporation, ice formation, convection or the effects of discharged gases on water at different temperatures. The paradoxicality of the effect of the MPEMBA is that the time during which the body cools up to the ambient temperature should be in proportion to the difference in the temperatures of this body and the environment. This law was still established by Newton and since then many times confirmed in practice. In this effect, water with a temperature of 100 ° C cools to a temperature of 0 ° C faster than the same amount of water with a temperature of 35 ° C. Nevertheless, it does not imply a paradox, since the effect of the MPEMBA can be found an explanation and within the framework of the famous physics. Here is a few explanations of the effect of MPEMBA: evaporation of hot water is evaporated faster from the container, thereby reducing its volume, and the smaller volume of water with the same temperature freezes faster. Maintaining up to 100 with water loses 16% of its mass when cooling to 0 C. Effect effect - double effect. First, the mass of water is reduced, which is necessary for cooling. And secondly, the temperature is reduced due to the fact that the heat of evaporation of the transition from the water phase to the steam phase is reduced. The temperature difference due to the fact that the temperature difference between hot water And the cold air is more - hence the heat exchange in this case is intensively and the hot water is faster cooled. Precooling When the water is cooled below 0 C It does not always freeze. Under some conditions, it can undergo hypothermia, continuing to remain liquid at temperatures below the temperature of the freezing point. In some cases, water may remain liquid even at a temperature of -20 C. The reason for this effect is that in order to begin to form the first ice crystals need crystal formation centers. If they are not in liquid water, then the supercooling will continue until the temperature decreases so much that the crystals will begin to form spontaneously. When they begin to form in a supercooled fluid, they will begin to grow faster, forming a Lorth Shuhuh, which freezing will form ice. Hot water is most susceptible to supercooling since its heating eliminates dissolved gases and bubbles, which in turn can serve as centers for the formation of ice crystals. Why does the supercooling cause hot water to stick faster? In the case of cold water, which is not overcooked by the following. In this case, the thin layer of ice will be formed on the surface of the vessel. This layer of ice will act as an insulator between water and cold air and will prevent further evaporation. The rate of formation of ice crystals in this case will be less. In the case of hot water, undergoing supercooling, supercooled water does not have a protective surface layer of ice. Therefore, it loses heat much faster through open top. When the process of hypothermia ends and water freezes, much more heat is lost and therefore more ice is formed. Many researchers of this effect consider supercooling to the main factor in the case of the MPEMB effect. Convection Cold water begins to freeze from above, thereby worsening the processes of heat emissions and convection, and hence the heat loss, while the hot water begins to freeze from below. This effect of water density anomaly is explained. Water has a maximum density at 4 C. If cooling water to 4 s and put it at a lower temperature, the surface layer of water will freeze faster. Because this water is less dense than water at a temperature of 4 s, it will remain on the surface, forming a thin cold layer. Under these conditions, the thin layer of ice will be formed on the surface of the water for a short time, but this layer of ice will serve as an insulator that protects the lower layers of water, which will remain at a temperature of 4 C. Therefore, the further cooling process will be slower. In the case of hot water, the situation is completely different. The surface layer of water will be cooled faster due to evaporation and greater temperature difference. In addition, cold water layers are more dense than hot water layers, therefore the cold water layer will fall down, lifting a layer of warm water to the surface. Such water circulation provides a rapid drop in temperature. But why does this process do not reach the equilibrium point? To explain the effect of the motion from this point of view of convection, it would be necessary to adopt that cold and hot water layers are separated and the convection process itself continues after average temperature Water drops below 4 C. However, there are no experimental data that would confirm this hypothesis that cold and hot water layers are separated during convection. Water dissolved in water in water always contains gases dissolved in it - oxygen and carbon dioxide. These gases have the ability to reduce water freezing point. When the water is heated, these gases are released from water, since their solubility in water high temperatures below. Therefore, when hot water is cooled, there are always fewer dissolved gases in it than in non-heated cold water. Therefore, the freezing point of heated water is higher and it freezes faster. This factor is sometimes considered as the main thing when explaining the effect of the MPEMB, although there are no experimental data confirming this fact. Thermal conductivity This mechanism can play a significant role when water is placed in the freezer of the refrigerator in small containers. Under these conditions, it is noted that the hot water container is shifted by a freezer ice from a freezer, thereby improving thermal contact with the freezer wall and thermal conductivity. As a result, the heat is removed from the container with hot water faster than from cold. In turn, the container with cold water does not shive below the snow. All these (as well as others) conditions were studied in many experiments, but a unambiguous answer to the question - which of them provide one hundred percent reproduction of the MPEMBE effect - and was not received. For example, in 1995, the German physicist David Auerbach studied the effect of water hypothermia on this effect. He found that hot water, reaching a supercooled state, freezes at a higher temperature than the cold, which means faster the latter. But cold water reaches a supercooled state faster than hot, thereby compensating for the previous lag. In addition, the results of Auerbakh contradicted the data obtained earlier that hot water is capable of achieving greater overcooling due to a smaller number of crystallization centers. When the water is heated from it, the gases dissolved in it are removed, and during its boiling, some salts dissolved in it are precipitated. You can say so far only one thing is possible - the reproduction of this effect significantly depends on the conditions in which the experiment is carried out. It is precisely because it is not always reproduced. O. V. Mosin
Mpemba effect (Paradox of MPEMBI) - a paradox that says that hot water at some conditions freezes faster than cold, although it must undergo the temperature of the cold water in the freezing process. This paradox is an experimental fact that contradicts the usual ideas, according to which, with the same conditions, the more heated body for cooling to a certain temperature requires more time than the less heated body for cooling to the same temperature.
This phenomenon was noticed at one time Aristotle, Francis Bacon and Rene Descart, but only in 1963, Tanzanian schoolboy Erassto Mpembea found that the hot mixture of ice cream freezes faster than cold.
As a student of Magambaba High School in Tanzania, Erasto Mpembea did practical work on the cook case. He needed to make homemade ice cream - boil milk, dissolve sugar in it, cool it to room temperature, and then put it in the fridge for freezing. Apparently, MPembba was not particularly a diligent student and priedered with the fulfillment of the first part of the task. Fearing that he would not have time for the end of the lesson, he put in the refrigerator still hot milk. To his surprise, it froze even earlier than the milk of his comrades cooked according to a given technology.
After that, MPEMBA experimented not only with milk, but also with ordinary water. In any case, already as a student of the Mkvava high school, he asked the question of Professor Dennis Osborne from the University College in Dar Es Salama (to read the students a lecture on physics in the university classroom: "If you take two identical containers with equal volumes of water So, in one of them, water has a temperature of 35 ° C, and in the other - 100 ° C, and put them in the freezer, then in the second water freezes faster. Why? " Osborne became interested in this issue and soon in 1969, together with Mpemba published the results of their experiments in the magazine "Physics Education". Since then, the effect found is called the effect of Mpemba.
Until now, no one knows how to explain this strange effect. Scientists have no single version, although there are many. It's all about the difference in the properties of hot and cold water, but it is not yet clear which properties play a role in this case: the difference in supercooling, evaporation, ice formation, convection or the effects of discharged gases on water at different temperatures.
The paradoxicality of the effect of the MPEMBA is that the time during which the body cools up to the ambient temperature should be in proportion to the difference in the temperatures of this body and the environment. This law was still established by Newton and since then many times confirmed in practice. In this effect, water with a temperature of 100 ° C cools to a temperature of 0 ° C faster than the same amount of water with a temperature of 35 ° C.
Nevertheless, it does not imply a paradox, since the effect of the MPEMBA can be found an explanation and within the framework of the famous physics. Here are a few explanations of the effect of MPEMBU:
Evaporation
Hot water faster evaporates from the container, thereby reducing its volume, and the smaller volume of water with the same temperature freezes faster. Heated to 100 with water loses 16% of its mass during cooling to 0 C.
Effect of evaporation - double effect. First, the mass of water is reduced, which is necessary for cooling. And secondly, the temperature is reduced due to the fact that the heat of evaporation of the transition from the water phase to the steam phase is reduced.
Temperature difference
Due to the fact that the temperature difference between hot water and cold air is more - therefore heat exchange in this case there is more intense and hot water is cooled faster.
Supercooling
When the water is cooled below 0 C It does not always freeze. Under some conditions, it can undergo hypothermia, continuing to remain liquid at temperatures below the temperature of the freezing point. In some cases, water can remain liquid even at a temperature of -20 C.
The reason for this effect is that in order to begin to form the first ice crystals need crystal formation centers. If they are not in liquid water, then the supercooling will continue until the temperature decreases so much that the crystals will begin to form spontaneously. When they begin to form in a supercooled fluid, they will begin to grow faster, forming a Lorth Shuhuh, which freezing will form ice.
Hot water is most susceptible to supercooling since its heating eliminates dissolved gases and bubbles, which in turn can serve as centers for the formation of ice crystals.
Why does the supercooling cause hot water to stick faster? In the case of cold water, which is not overcooked by the following. In this case, the thin layer of ice will be formed on the surface of the vessel. This layer of ice will act as an insulator between water and cold air and will prevent further evaporation. The rate of formation of ice crystals in this case will be less. In the case of hot water, undergoing supercooling, supercooled water does not have a protective surface layer of ice. Therefore, it loses heat much faster through open top.
When the process of hypothermia ends and water freezes, much more heat is lost and therefore more ice is formed.
Many researchers of this effect consider supercooling to the main factor in the case of the MPEMB effect.
Convection
Cold water begins to freeze from above, thereby worsening the processes of heat emission and convection, and therefore heat loss, while hot water begins to freeze from below.
This effect of water density anomaly is explained. Water has a maximum density at 4 C. If cooling water to 4 s and put it at a lower temperature, the surface layer of water will freeze faster. Because this water is less dense than water at a temperature of 4 s, it will remain on the surface, forming a thin cold layer. Under these conditions, the thin layer of ice will be formed on the surface of the water for a short time, but this layer of ice will be an insulator that protects the lower layers of water, which will remain at a temperature of 4 C. Therefore, the further cooling process will be slower.
In the case of hot water, the situation is completely different. The surface layer of water will be cooled faster due to evaporation and greater temperature difference. In addition, cold water layers are more dense than hot water layers, therefore the cold water layer will fall down, lifting a layer of warm water to the surface. Such water circulation provides a rapid drop in temperature.
But why does this process do not reach the equilibrium point? To explain the effect of the MPEMBA from this point of view of convection, it would be necessary to make that cold and hot water layers are separated and the convection process itself continues after the average water temperature drops below 4 C.
However, there are no experimental data that would confirm this hypothesis that cold and hot water layers are divided during convection.
Dissolved gases
Water always contains gases dissolved in it - oxygen and carbon dioxide. These gases have the ability to reduce water freezing point. When the water is heated, these gases are released from water, since their solubility in water at high temperatures below. Therefore, when hot water is cooled, there are always fewer dissolved gases in it than in non-heated cold water. Therefore, the freezing point of heated water is higher and it freezes faster. This factor is sometimes considered as the main thing when explaining the effect of the MPEMB, although there are no experimental data confirming this fact.
Thermal conductivity
This mechanism can play a significant role when water is placed in the freezer of the refrigeration chamber in small containers. Under these conditions, it is noted that the hot water container is shifted by a freezer ice from a freezer, thereby improving thermal contact with the freezer wall and thermal conductivity. As a result, the heat is removed from the container with hot water faster than from cold. In turn, the container with cold water does not shive below the snow.
All these (as well as others) conditions were studied in many experiments, but a unambiguous answer to the question - which of them provide one hundred percent reproduction of the MPEMBE effect - and was not received.
For example, in 1995, the German physicist David Auerbach studied the effect of water hypothermia on this effect. He found that hot water, reaching a supercooled state, freezes at a higher temperature than the cold, which means faster the latter. But cold water reaches a supercooled state faster than hot, thereby compensating for the previous lag.
In addition, the results of Auerbakh contradicted the data obtained earlier that hot water is capable of achieving greater overcooling due to a smaller number of crystallization centers. When the water is heated from it, the gases dissolved in it are removed, and during its boiling, some salts dissolved in it are precipitated.
You can say so far only one thing is possible - the reproduction of this effect significantly depends on the conditions in which the experiment is carried out. It is precisely because it is not always reproduced.
21.11.2017 11.10.2018 Alexander Feri
« What water freezes faster cold or hot?"- try to ask a question with your familiar, most likely most of them will answer that cold water freeze faster - and make a mistake.
In fact, if you simultaneously put two models in the freezer and volume of the vessel, in one of which there will be cold water, and in a different one, then hot water will be frown faster.
Such an approval may seem absurd and unreasonable. If you follow logic, then hot water should first cool down to the temperature of the cold, and the cold at that time should already turn into a lot.
So why is hot water overtakes cold on the way to freezing? Let's try to figure out.
History of observations and research
Paradoxical effect people have observed for a long time, but no one attacked him much importance. So not docked in the speed of frozen cold and hot water noted in his records arrest, as well as Rene Descartes and Francis Bacon. An unusual phenomenon was often manifested in everyday life.
For a long time, the phenomenon did not have been studied and did not make much interest among scientists.
The beginning of the study of an unusual effect was found in 1963 when an inquisitive schoolboy from Tanzania - Erasto Mpembea, noticed that hot milk for ice cream freezes faster than cold. In the hope of obtaining an explanation of the causes of an unusual effect, the young man asked his physician teacher at school. However, the teacher only laughed at him.
Later, MPemba repeated the experiment, but in his experience, he used no longer milk, and the water and paradoxical effect repeatedly repeatedly.
After 6 years - in 1969, Mpembea asked this question to Professor Physician Dennis Osborne who came to his school. Professor interested in observation of the young man, as a result, an experiment was conducted, which confirmed the effect of the effect, but there was no causes of this phenomenon.
Since then, the phenomenon was called the effect of Mpemba.
In the entire history of scientific observations, a variety of hypotheses on the causes of the phenomenon were put forward.
So in 2012, the British royal chemical society would be announced a contest of hypotheses explaining the effect of the MPEMBA. In the competition, scientists from around the world participated, 22,000 were registered scientific work. Despite such an impressive number of articles, none of them made clarity into the paradox of the MPEMB.
The most common version was performed according to which, hot water freezes faster, as it just evaporates faster, it becomes less, and as the volume decreases, its cooling speed increases. The most common version was eventually refuted as an experiment was conducted, in which evaporation was excluded, and the effect was nevertheless confirmed.
Other scientists believed that the cause of the effect of the MPEMBA is to evaporate dissolved in water gases. In their opinion, in the process of heating the gases dissolved in water are evaporated, due to which it takes on a higher density than the cold. As you know, the increase in density leads to a change physical properties water (increasing thermal conductivity), and consequently an increase in the cooling rate.
In addition, a number of hypotheses were put forward, which describe the rate of water circulation, depending on the temperature. In many studies, an attempt was made to establish the relationship between the container material in which the liquid was located. Very many theories seemed very believable, but scientifically confirm them did not succeed due to the lack of initial data, contradictions in other experiments, or due to the fact that the identified factors were simply not comparable with the speed of cooling the water. Some scientists in their works questioned the existence of the effect.
In 2013, researchers from Technological University Nanyang in Singapore stated that they solved the mystery of the effect of the MPEMBA. According to the research conducted by them, the cause of the phenomenon lies in the fact that the amount of energy stored in hydrogen bonds between the cold and hot water molecules is significantly different.
Computer simulation methods have shown the following results: the higher the water temperature, the larger the distance between molecules due to the fact that the repelling forces increase. And in consequently, hydrogen bonds of molecules are stretched, a substantial amount of energy. When cooled, the molecules begin to close with each other, releaseing energy from hydrogen bonds. In this case, the return of energy is accompanied by a decrease in temperature.
In October 2017, Spanish physicists, during the next study, found out that a large role in the formation of the effect plays exactly the removal of a substance from equilibrium ( strong heating Before a strong cooling). They determined the conditions at which the probability of the effect of the effect is maximum. In addition, scientists from Spain confirmed the existence of the reverse effect of the MPEMB. They revealed that when heated, a colder sample can achieve a high temperature faster than warm.
Despisable information and numerous experiments, scientists intend to continue learning the effect.
MPEMBA effect in real life
And you thought about it, why in winter the roller is poured with hot water, and not cold? As you already understood, do it because the roller filled with hot water will frozen faster than if it was filled with cold. For the same reason, the slides in the winter ice towns are filled with hot water.
Thus, knowledge of the existence of a phenomenon allows people to save time in the preparation of sites for winter sports.
In addition, the effect of the scan is sometimes used in industry - to reduce frost products, substances and materials containing water.
Water is one of the most amazing liquids in the light that unusual properties are inherent. For example, ice is a solid condition of the fluid, has a specific weight lower than the water itself, which made the emergence and development of life on Earth. In addition, there are discussions in the near-scientific, and the scientific world about which water freezes faster - hot or cold. The one who proves the faster freezing of hot fluid in certain conditions and scientifically justifies its decision, will receive from the British Royal Society of Chemists a reward in 1000 pounds.
History of the question
The fact that when performing a number of conditions for hot water in the speed of freezing is ahead of the cold, it was noticed in the Middle Ages. The explanation of this phenomenon was spent a lot of effort to Francis Bacon (Francis Bacon) and René Descartes. However, from the point of view of classical heat engineering, this paradox is impossible to explain, and they tried to shy about it. A somewhat curious story that happened to Tanzanian schoolboy Erasto Mpemba in 1963 was the impetus for the continuation of the disputes. One day during the cooking lesson in the school of cooks, the boy, distracted by outsiders, did not have time to cool the mixture for ice cream on time and put a sugar solution in the freezer in the freezer hotter. For his surprise, the product cooled somewhat faster than his fellow workers temperature mode Creating ice cream.
Trying to understand the essence of the phenomenon, the boy appealed to the physics teacher, which, without going into details, ridiculed his culinary experiments. However, Erasto was distinguished by enviable perseverance and continued its experiments no longer on milk, but on the water. He was convinced that in some cases the freezing of hot water occurs faster than cold.
Entering University in Dar Es Salaam, Erasto Mpember visited the lecture of Professor Denis Osborne (Dennis G. Osborne). After her end, the student puzzled the scientist about the rate of freezing of water depending on its temperature. D.G. Osborne ridicked the question itself, saying with aplomb that any two-room is known that cold water will freeze faster. However, the natural perseverance of the young man made itself felt. He signed a bet with Professor, offering here, in the laboratory, to conduct an experimental check. Erasto placed two containers with water in the freezer, the temperature of which in one was equal to 95 ° F (35 ° C), and in the second - 212 ° F (100 ° C). What was the surprise of professors and the surrounding "fans" when the water in the second container frozen faster. Since then, this phenomenon has received the name of the "Paradox of MPEMS".
However, so far there is no slender theoretical hypothesis explaining the Paradox of MPEMBA. Not clear what external factors chemical composition Water, the presence of dissolved gases and minerals in it affect the freezing rate of fluids at different temperatures. The paradoxicality of the "MPEMBE effect" is that it is contrary to one of the laws open by I. Newton, which states that the time of cooling water is directly proportional to the difference in fluid temperature and the environment. And if all other fluids are completely obeyed by this law, the water in some cases is an exception.
Why hot water faster frozent.
There are several versions, why hot water freezes faster than cold. The main ones are considered:
- hot water evaporates faster, while its volume decreases, and the smaller fluid volume cools faster - when water is cooling from + 100 ° C to 0 ° C, the volumetric losses with atmospheric pressure reach 15%;
- the heat exchange intensity between the liquid and environmental the higher the greater the temperature difference, therefore thermal losses boiling water are faster;
- when cooled hot water on its surface, the cry is formed, which prevents the complete freezing of the liquid and its evaporation;
- at high water temperature, its convection mixing occurs, the reduction time of the freezing;
- the gases dissolved in water decrease the freezing point, selecting the energy to crystal formation, - there are no dissolved gases in hot water.
All these conditions were repeatedly subjected to experimental verification. In particular, the German scientist David Auerbach (David Auerbach) found that hot water crystallization temperature is slightly higher than that of cold, which makes it possible to faster freezing the first. However, later his experiments were criticized and many scientists are convinced that the "MPMBE effect" about what water freezes faster - hot or cold, it is possible to reproduce only under certain conditions, the search and concretization of which no one has been engaged in the current time.
