According to people’slifeAs a rule of thumb, heating an object seems to be much faster than making it cold. For example, when we put to:foodput it in the microwave oven and it can heat up to 100°C or higher in a few minutes; If you want to lower the temperature of the food, it will take much longer.
Traditional thermodynamics believes that heating and cooling are essentially “mirrors” of each other, and that these two fundamental thermodynamic processes should be symmetrical and follow similar paths.
However, a study published in “natureA paper in the journal Physics challenges the traditional view of thermodynamics. Experiments conducted by European researchers using silica microspheres show that our life experience is right and traditional thermodynamics is wrong. They reveal the essential asymmetry of heating and cooling and their evolution along different paths.
Heating speed is faster than cooling speed
Most of us have an intuitive sense of temperature. For example, if you feel hot today, the temperature is high; If you feel cold, that is the low temperature. However, this is not the essence of temperature. Physicists have debated for centuries how to define temperature accurately. School textbooks may say that temperature is the molecular heat inside an objectmotionMeasure of strength.
Thermodynamics is the study of the relationship between heat and other forms of energy, and it describes temperature as a measure of how many different values (such as velocity or energy) configurations all atoms in a system can have. These configurations are called “microstates”. Based on this understanding, traditional thermodynamics believes that heating and cooling are symmetrical in nature and are two processes that mirror each other. However, this theory assumes that the change in temperature will either occur slowly or very little.
When an object heats up or cools over a long period of time, traditional thermodynamics may “fail”, and the result may even be counterintuitive. For example, heatwaterIt freezes more easily than warm water, a phenomenon known as the Mpamba effect.
Now, the University of Granada in Spain is multidisciplinary with Max Planck in GermanyscienceResearchers at the institute have discovered a new phenomenon: microscopic spheres of silica under the action of an electric field exhibit significant asymmetry during heating and cooling, that is, heating faster than cooling speed.
Carry out the “hot spring bath” small ball experiment
At the microscopic level, heating and cooling involve the process of energy exchange and redistribution between various particles within a system. Heating involves injecting energy into individual particles, intensifying their motion; Refrigeration, on the other hand, releases energy and inhibits its movement. butWhyIs the heating process always more efficient than the cooling process?
To answer this question, the new research focuses on understanding the dynamics of microsystems that undergo thermal relaxation, that is, how these systems evolve from a state to an equilibrium state when temperature changes. To do this, the researchers employed sophisticated experimental setups to observe and quantify this process.
At the heart of the experiment is:lightTweezers, a powerful technology that uses a laser to capture individual particles made of silica or plastic. The researchers placed tiny spheres in water and captured them using lasers. The temperature of the particles’ surroundings is then controlled by applying an electric field, similar to soaking particles in a “hot spring bath,” and the degree of jitter and movement of the particles is measured. They repeated this process tens of thousands of times.
Measuring a single particle in this way is equivalent to measuring a single microscopic state. Such measurements are not possible for materials composed of many particles, as they may have countless configurations. But by taking multiple measurements of a single microscopic particle, the team was able to map out the number of microscopic states that could occur.
“These particles collide with water molecules and move in a distinctly random way. When they are confined to a small area by forceps, they perform what is known as Brownian motion. “explains Professor Raul Rika Alarcón of the University of Granada in Spain. The higher the temperature of the water, the more frequent and violent the collision of these particles with water molecules, and the more intense the Brownian motion. ”
On the other hand, the lower the temperature of water, the energy of individual particles is released and the movement is inhibited.
Propose “Law 2.5 of Thermodynamics”
The researchers then measured how many different microscopic states these particles need to go through as they transition between the two temperatures through heating or cooling. They found that the number of microscopic states that particles need to go through during heating is smaller than during the cooling process, which means that the heating process is faster.
They proposed a new theoretical framework called thermokinematics to explain this asymmetry. It has been found that there is asymmetry between heating and cooling between any two temperatures, and thermokinematics provides a way to quantitatively explain this phenomenon.
Aljaz Goldek of the Max Planck Institute for Multidisciplinary Sciences said that although it is unclear why this fundamental difference exists and that it is not common, it should be present in any system with a sufficiently large heating or cooling amplitude. This is because such large temperature changes often cause changes in the system itself, such as freezing or boiling, masking this newly observed effect. Goldek believes that this asymmetry may be important to help improve the efficiency of Brownian heat machines, microcargo transport motors, and self-assembled or self-healing materials.
The second law of thermodynamics states that heat can always only be transferred from hot to cold. For example, cooked meals can get cold if not eaten in time;RefrigeratorThe ice cream taken out will melt by absorbing ambient heat. But Janet Anders of the University of Exeter in the UK believes that the second law does not talk about speed, but only about possibility. The newly discovered effect can almost be considered an additional law of thermodynamics, an extension of the second law.
“The new theory, which I call ‘Law 2.5 of Thermodynamics,’ holds that any process can occur, but some of them take a little longer than the reverse process.” Anders said.
