The mini refrigerator is actually a “distant relative” of the “nuclear power plant”?

　　In the hot summer, five minutes outside the home can make people sweat profusely. In order to drink a can of iced Coke, you can buy a mini refrigerator for tens of yuan. It can not only cool down, but also become a heating box in winter. But is this cheap and cold refrigerator really reliable?
Is the mini fridge a “proper” fridge?

　　This kind of mini refrigerator and the large refrigerator at home, except that there is a refrigerator in the name, the refrigeration principle can be said to have nothing to do with it. The core element of the mini refrigerator is a semiconductor refrigeration chip.
　　The structure of this semiconductor refrigeration chip is very simple: a small square piece and two wires. When electricity is applied to the cooling chip, one side of the small square will heat up and the other side will cool down. After changing the direction of power supply, the heating surface and the cooling surface will also be reversed, and the small refrigerator using semiconductor refrigeration chips can both cool and heat. Moreover, the voltage required by the semiconductor refrigeration sheet is also very low, and it can be powered by a power bank. Most of the car refrigerators in the car are also semiconductor refrigeration.
　　The peltier cooler sticks two different semiconductor materials together, and then leads a wire from each of the two materials. When working, connect the wire to a DC power supply, and the heat will be transferred from one material to another, showing that one side is cooling and the other side is heating.

semiconductor cooler

The structure of the semiconductor refrigerator

　　This phenomenon is called the Peltier effect. This effect was discovered in 1834 by French physicist JCA Peltier. Peltier was originally a watchmaker, but at the age of 30, he started experiments and observations in physics. His daily life is either boiling water in the Alps and measuring the temperature of boiling water, or observing waterspouts by the sea and thinking about how tornadoes are formed.
　　However, it is precisely because of these seemingly “useless” actions that many “useful” scientific principles have been produced.
The principle of non-“serious” refrigerators is widely used

　　With the development of physics becoming more and more perfect, scientists have summed up the Peltier effect and the effects discovered by two other scientists, collectively known as the thermoelectric phenomenon. Machines made using these three phenomena are now spread all over the world.
　　Seebeck Effect: When two different conductors are connected into a loop and the materials on both sides have different temperatures, a current will flow in the circuit. This effect is the inverse of the Peltier effect. That is to say, take a semiconductor cooling chip and create a temperature difference on both sides (for example, stick ice cubes on one side and put a heat preservation bag on the other side), and this semiconductor cooling chip will become a generator that uses the temperature difference to generate electricity.
　　Thomson effect: When a current flows through a uniform conductor with a temperature gradient (a piece of iron wire with one end hot and the other cold), the conductor will absorb or release a certain amount of heat.
　　The semi-conductor refrigeration sheet made of the Peltier effect allows us to enjoy iced cola and hot milk tea, but power generation depends on the Seebeck effect: temperature difference + thermoelectric converter = generator.

A small kettle thermoelectric generator developed by scientists during World War II

　　During World War II, the Soviet guerrillas suffered from the lack of places to charge radio stations, and ordinary generators were large and noisy. So they commissioned scientists to develop a kettle thermoelectric generator based on the Seebeck effect. It looks no different from an ordinary kettle, but it uses the temperature difference of about 300°C between the campfire and the water to generate electricity, and this The charging power of the generator can reach 6 watts.
Small “Nuclear Power Plant”

　　Because the thermoelectric generator itself has no moving parts, it has become the darling of the aerospace industry because of its durable construction.
　　When conducting deep space exploration missions, the spacecraft may be far away from the sun or in a shadowed area, with severe insufficient illumination and low temperature environment. The power supply of the spacecraft in this environment is a big problem.
　　The solution to this problem is the radioisotope thermoelectric generator, or RTG for short. RTGs use the Seebeck effect to convert the heat generated by the decay of radioactive isotopes into electricity.
　　The power generation process of RTG is divided into the decay heat collection stage and the thermoelectric power generation stage. Take a typical RHU/RTG as an example: when the radioactive element (plutonium-238) decays, it will release rays, and the high-energy particles that make up the rays will be prevented from interacting with the surrounding substances. and absorption, a process that generates heat. With a long-lasting heat source, the power generation capacity of RHU/RTG is also very long-lasting and stable, and the waste heat generated during power generation can keep the spacecraft warm, killing two birds with one stone.
　　The RTG installed on the “Voyager 2” probe has been working stably for 45 years. The Curiosity Mars train and the Chang’e 4 lander are also equipped with RTGs. Therefore, RTG can even overcome the extreme environment of the universe, and the extreme environment on the earth is a piece of cake for it.

The RTG on the tail of the Curiosity rover

　　In the arctic winter with the long polar night, the energy supply of the lighthouse depends on RTG. As of 1992, the military installations deployed by the US military in the Arctic also use RTGs for power supply. Miniaturized plutonium-238 batteries were once also used as pacemaker batteries.
　　With the emergence of flexible circuits and new materials, the performance of devices made using thermoelectric phenomena will also be greatly improved. Perhaps future smart watches will be able to obtain sufficient power by using the temperature difference between the human skin and the air, or by implanting flexible semiconductor cooling devices into clothes, you can get a cooling suit that is not afraid of summer.