Galactic Tech Empire

Chapter 403 Thermoelectric Power Generation
Huang Haojie flipped through the information on ion emission and photon emission one by one. Many of these materials are theoretical papers. Of course, there are still many practical applications in ion emission.

Milijia, Sun Nation, and Xizhou Alliance all have satellites or detectors with ion beams, especially for deep space probes. Plutonium isotope batteries can only fly for decades with ion beams.

Otherwise, there is no way for those detectors that have been flying for decades to use chemical fuel engines.

After watching it for a long time, there are still very few useful solutions to the heat problem of nuclear fusion miniaturization.

However, ion hair and photon hair still have great potential. Huang Haojie asked Zhong:
"I remember if we had an ion engine institute?"

[Yes, the Institute of Ion Engines is in Keelung City, the director is Botong Zhou, and the chief engineer is Ji Mishima. ]
"Zhou Botong?" Huang Haojie raised his head curiously.

［╭(′ o ′)╭ is a blogger who is knowledgeable and versatile. ]
"Eh..." Huang Haojie was embarrassed, and quickly changed the subject:

"Send the small reactors No. 5, 6, and 7 in my laboratory to the Ion Engine Research Institute, let them study the ion engine for nuclear fusion, and give them the task of the photon engine by the way."

[OK. ]
After Huang Haojie gave this order, he focused on thermoelectric power generation, which is a simple and direct power generation technology.

There is no need for complicated equipment, as long as a special material called "thermoelectric material" is applied with a temperature difference between its two ends - for example, one end is cold water at 27 degrees Celsius, and the other end is boiling water at 100 degrees Celsius, the temperature difference of 73 degrees Celsius , you can make this material emit a certain power of electricity.

Since there are so many advantages and great potential of power generation technology, why is it rarely heard of its application?
Because thermoelectric power generation has a fatal flaw - the efficiency is too low.

The thermal efficiency of the best existing thermoelectric power generation materials is less than half of that of conventional thermal power plants, which is even lower than that of geothermal power generation (the efficiency of geothermal power generation is about 6-18%). Those capitalists are not stupid with such a low thermal efficiency Fork, how could you do such a loss-making business.

However, when Huang Haojie read a paper published in Nature, he found that this paper gave him a lot of inspiration.

This paper was published by a research team led by Professor Ernst Bauer of the Western European Union-Technical University of Vienna, Austria.

The data in the paper show that they have doubled the thermoelectric figure of merit (ZT value), a key performance indicator for thermoelectric power generation materials.

The thermoelectric material they developed has a thermoelectric figure of merit as high as 5 to 6, compared with the best previous materials of about 2.5 to 2.8.

Huang Haojie immediately focused on it, and asked Zhong to collect the team's information on thermoelectric materials. After a while, a lot of information appeared in his holographic computer.

In order to improve thermoelectric efficiency in thermoelectric power generation, the ZT value of thermoelectric materials must be increased. Only when the ZT value reaches or exceeds 4, this technology has commercial value.However, more than 100 years have passed since the thermoelectric effect was discovered, and it is difficult for scientists to even achieve 3.

Why is it so difficult to increase the ZT value of thermoelectric materials? This starts with the physical principle on which thermoelectric power generation technology relies—the thermoelectric effect itself.

There are a certain number of carriers (such as electrons or holes) inside the metal or semiconductor, and the density of these carriers will change with the change of temperature. If one end of the object has a high temperature and the other end has a low temperature, Different carrier densities will appear in the same object.

As long as the temperature difference between the two ends of the object can be maintained, the carriers can continue to diffuse, thereby forming a stable voltage. This is the principle of thermoelectric power generation.

The efficiency of thermoelectric power generation depends on three important characteristics of thermoelectric materials:
First, the Seebeck coefficient (the ability of a material to generate an electromotive force under a temperature difference), the higher the Seebeck coefficient, the higher the electromotive force generated under the same temperature difference, which means that the more electricity can be emitted.

Second, the conductivity (the conductivity of the material). The higher the conductivity, the easier it is for electrons to diffuse inside the material.

Third, thermal conductivity (the thermal conductivity of the material). The higher the thermal conductivity, the faster the heat can be transferred from the hot end to the cold end, so that the temperature difference on which thermoelectric power generation depends disappears, and the electromotive force also disappears. .

Obviously, for thermoelectric materials, the stronger the first two abilities, the better, while the weaker the latter ability is, the better.

The thermoelectric figure of merit ZT is a collection of these three parameters: the higher the Seebeck coefficient, the higher the electrical conductivity, and the lower the thermal conductivity, the higher the ZT value, and the higher the efficiency of the material for thermoelectric power generation.

Therefore, the key to the study of thermoelectric materials is how to increase the ZT value of the material, that is, to obtain low thermal conductivity while achieving high Seebeck coefficient and electrical conductivity.

However, it is very difficult to optimize these three parameters at the same time.Because these three properties are interrelated, the improvement of one property is often accompanied by the weakening of the indicators of the other or even two properties.

In general, increasing the Seebeck coefficient of a material reduces its electrical conductivity.The interrelated nature of these three parameters has kept the development of thermoelectric materials slow.

However, the relationship between the three parameters "one loses and one wins and one prospers" is not completely absolute.

This "community of interests" also has a "traitor" - thermal conductivity, more precisely, a part of thermal conductivity.The thermal conductivity of a material consists of two components, electronic thermal conductivity and phonon thermal conductivity.

Among them, the former is closely related to electrical conductivity and is a member of the "community of interests"; however, phonon thermal conductivity is the only one among the various parameters that determine the properties of thermoelectric materials that has no effect on all other parameters in the ZT value. parameters.

The research idea of ​​the University of Vienna team is to reduce the overall thermal conductivity by reducing the phonon thermal conductivity without affecting the electronic thermal conductivity of the material.

Specific to the microscopic level of the material, it is to enhance the scattering of phonons through some special structures under the premise of not affecting the electron transport, so as to only reduce the phonon thermal conductivity of the material without changing other parameters.

Starting in 2013, after years of research, they discovered a material that can simultaneously achieve high electronic thermal conductivity and low phonon thermal conductivity.

Using a layer of alloy material composed of iron, vanadium, tungsten and aluminum elements covering the silicon crystal, a ZT value as high as 5 to 6 is achieved, which doubles the ZT value compared to the existing best level.

Under normal circumstances, this alloy composed of four elements: iron, vanadium, aluminum, and tungsten has a very regular structure. For example, there must be only iron atoms next to vanadium atoms, and the same is true for aluminum atoms, while two adjacent elements of the same element The distance between atoms is also always the same.

However, when the scientists combined a thin layer of the material with a silicon substrate, something magical happened.

Although the atoms still maintain the original cubic structure, the relative positions of the atoms have changed drastically.

Where a vanadium atom should have appeared before, it may now be an iron atom or an aluminum atom; and an iron atom next to an aluminum atom may still be an aluminum atom, or even a vanadium atom.

Moreover, this change of position between atoms is completely random and has no rules to follow.

This combination of order and disorder in the crystal structure gives the material its unique properties:

Electrons can still have their own special path and "freely" shuttle in the crystal, so that the electrical conductivity and electronic thermal conductivity are not affected; but the phonon migration that heat conduction depends on is blocked by the irregular structure, resulting in phonon thermal conductivity rate dropped significantly.

In this way, the temperature difference between the hot and cold ends is maintained and the resulting potential difference does not disappear.

The team at the University of Vienna also achieved the coveted goal of keeping the electronic thermal conductivity of thermoelectric materials unchanged and the phonon thermal conductivity decreasing, thereby greatly increasing the ZT value to 6.

In their theory, if the topological structure of related conceptual materials can be changed, the ZT value reaching 20 will no longer be just a dream.

When the ZT value reaches 6, the thermal efficiency will reach about 12%. If the ZT value can be increased to 20, the thermal efficiency can be compared with that of a steam turbine.

Compared with steam turbines, thermoelectric power generation equipment has an extremely simple structure, such as the plutonium isotope battery mentioned above, which is a thermoelectric power generation battery.

However, in terms of materials science, Huang Haojie is not as good as the orthodox Li Xiang and the others. He quickly sent a research topic to the Materials Research Institute, asking the Materials Research Institute to develop a thermoelectric material with a ZT value of around 20.

　This is an update today!That inauspicious chapter number was skipped.

　　
　
(End of this chapter)