The refrigerator is now one of the most common household appliances in every household. In China in the 1980s, refrigerators are one of the “four big pieces” that symbolizes the prosperity of life. It can be seen that refrigerators are very important in our daily life. But like a car, the refrigerator has a negligible effect on the environment while it is convenient for people.
The working principle of the traditional refrigerator is called steam compression. The refrigerant liquid in the refrigerator pipe absorbs the heat generated by the stored food and turns into a gas. The gas entering the refrigerator releases the heat to cool the liquid, and then enters the pipeline again to cool the food. This cycle repeatedly maintains the low temperature inside the refrigerator. However, the negative impact of refrigerant gas on the environment cannot be ignored. These gases seriously damage the earth’s umbrella, the ozone layer, and exacerbate the greenhouse effect. The experimental results show that one kilogram of refrigerant contributes two tons to the greenhouse effect. carbon dioxide.
Is there a more environmentally friendly refrigerant? The main alternatives we think of today are hydrocarbons such as R134a (tetrafluoroethane) and R600a (isobutane). But this is just a transitional expediency, because R134a fluorine is still harmful to the atmosphere, R600a is relatively more environmentally friendly, but it will emit flammable and explosive gases, and safety is not guaranteed.
Is there any good substitute? Recently scientists have found a better refrigerant – plastic crystals, a solid refrigerant.
What is a plastic crystal?
Particles that make up a substance, such as atoms, molecules, etc., are regularly arranged to form a solid substance. We call it a crystal. The crystal has a symmetrical shape and a fixed melting temperature, such as salt, ice, and metal. The order of the particles inside the plastic is irregular, and there is no fixed melting temperature. After heating to a certain extent, the plastic will always melt, so the plastic is not a crystal.
However, there is a material that has both crystalline and plastic properties and is called a “plastic crystal.” The molecular structure of the plastic crystal exhibits a high degree of disorder, that is, the lattice arrangement is irregular; however, relatively small pressure can induce changes in these structures, thereby switching between crystal and amorphous. Therefore, these materials are highly compressible and reversible, that is, they can be restored to their original shape after compression. This property is called “plasticity”. Because this new material is plastic, it is named as a plastic crystal. For example, neopentyl glycol, recently studied by scientists at the Chinese Academy of Sciences, is a plastic crystal material that can be used as a new solid-state refrigerant for refrigerators.
A new era of solid refrigeration
The advantage of a plastic crystal as a refrigerant is that when the plastic crystal is under the influence of an external force, its internal molecular arrangement changes, and at this time, it not only changes the shape, but also generates a large energy change, thereby changing the temperature. The traditional refrigerator uses a compressor to control the pressure, so that the liquid refrigerant changes its shape and temperature to adjust the temperature in the refrigerator. The plastic crystal replaces the traditional liquid refrigerant and regulates the temperature.
Initially, the molecules of the plastic crystal are randomly arranged, and their temperature is consistent with room temperature. At the beginning of the cycle, the compressor is pressurized, and the molecules in the plastic crystal change from disordered to ordered and the temperature rises. The heat sink inside the refrigerator discharges the heat of the plastic crystal to the external environment, and the temperature of the crystal returns to the initial value, but the molecular arrangement is still ordered. After the compressor pressure disappears, the crystal molecules return to the disordered state. At this time, its temperature drops drastically, far below the initial temperature. The plastic crystal can absorb the heat emitted from the food inside the refrigerator, and wait until the temperature inside the crystal and the refrigerator are the same. The compressor is pressurized again and enters the next cycle.
Scientists have found that the molecular arrangement of neopentyl glycol from ordered to disordered, the temperature drops by dozens of times that of conventional refrigerants, so the solid refrigerant no longer needs to flow and maintain The low temperature inside the entire refrigerator.
Because the plastic crystal is solid state throughout the refrigeration process, it does not produce gas that damages the atmosphere and causes the greenhouse effect, and it is not threatened by high-pressure gas when it is used. It does not require a dense steam-sealed piping system, and the new refrigerator can be manufactured. In any shape, the cooling system can even be scaled down to a single microchip, which greatly increases the portability of the refrigerator. However, there is still a problem to be solved by relying on plastic crystal cooling. Compared with conventional refrigerators, plastic crystals require more external force to change the molecular state, which means that more energy is needed. Researchers are experimenting with more energy-efficient methods, and maybe two or three years later we can see such a new environmentally friendly new refrigerator.