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More and more scientists have begun to pay attention to energy conservation and environmental protection. The traditional heating method is to burn fossil fuels, such as oil and coal, to obtain heat; however, this process inevitably produces harmful substances (carbon dioxide and solid waste) and damages the environment. In order to improve energy efficiency and reduce environmental pollution, China has implemented a large-scale "coal to electricity" policy. By using electric heating equipment autonomously, electrical energy can be converted into thermal energy, thereby effectively reducing environmental pollution and promoting the development of a low-carbon society. Traditional electric heating materials are mainly metal-based. For example, Cu-based and Fe-Cr-Al-based alloy electric heating materials have a wide range of applications. However, metal-based electric heating materials have high cost, low thermal efficiency, complex preparation process, and are susceptible to acid and alkali corrosion. In contrast, non-metal-based electric heating materials, such as carbon-based electric heating materials, have become excellent candidates to replace metal-based electric heating materials due to their light weight, good thermal and electrical conductivity, and high electric heating efficiency. Carbon-based electric heating materials are usually prepared by dispersing carbon nanoparticles such as graphene, carbon black, carbon nanotubes (CNTs) or other highly conductive nanoparticle fillers into a substrate. In recent years, graphene and carbon nanotubes have received extensive attention as the main fillers and are research hotspots in the field of carbon materials, with graphene accounting for 40.35% and carbon nanotubes accounting for 35.09%. However, several chemicals are used in the preparation of graphene oxide, which can cause serious explosion hazards and environmental pollution.
The main point of this paper
Characteristics of carbon nanotubes (CNTs):
CNTs are ideal materials for electric heating elements due to their light weight, high aspect ratio, large specific surface area, high strength and modulus, excellent electrical and thermal conductivity, and chemical stability
Classification of CNTs:
CNTs can be divided into two types: single-walled (SWCNT) and multi-walled (MWCNT)
Dispersion challenges of CNTs:
Due to the strong intermolecular forces and chemical inertia between CNTs, they are difficult to disperse and easily form bundles or clusters, which limits their large-scale application in electric heating
Surface functionalization of CNTs:
In order to improve the uniform distribution of CNTs in different solutions, the surface of CNTs needs to be functionalized, such as carboxylation of MWCNTs to stabilize in different solvents
CNTs and polymer composite electric heating materials:
By combining CNTs with polymer substrates, electric heating composite materials can be prepared. For example, Yang et al. blended CNTs with aramid fibers to achieve uniform distribution of CNTs in the composite material, and the surface temperature of the electrothermal material can reach 203°C
Preparation of CNTs film:
Xu et al. prepared CNTs film using chemical vapor deposition method, and its surface temperature can reach 206°C at 2 V input voltage
Advantages of electrospinning process:
Electrospinning process does not rely on adding a large number of CNTs with high conductivity particles, is easy to operate, and is suitable for large-scale practical applications
Preparation method:
CNT/CNF composite electrothermal film was prepared by electrospinning.
Influencing factors:
The conductivity of CNT/CNF composite electrothermal film is directly affected by the carbon nanotube content and carbonization temperature.
Electrothermal performance:
The electrothermal performance is positively correlated with the CNT content, carbonization temperature and applied voltage.
Temperature control:
The surface temperature of CNT/CNF can be controlled within the range of 30-260℃.
Durability:
The composite material has no loss after 100 consecutive heating and cooling.
Heat transfer controllability:
The convection heat transfer with air is controllable within the range of 0.008 ~ 31.75 W/m²K.
Radiative heat transfer is controllable within the range of 0.29 ~ 1.92 W/m²K.
Heat transfer efficiency:
The heat transfer efficiency of CNT/CNF is as high as 94.5%.
Rapid heating capability:
CNT/CNF composites can melt 1 cm thick ice in 3 minutes through thermal convection and thermal radiation alone.
Electrospinning technology is used to cleverly insert carbon nanotubes into the inner surface of CNF. Due to the excellent physical and chemical properties of CNF, its electrical conductivity and electrothermal properties can be further improved. CNT/CNF does not require a large driving voltage, only a safe voltage (<36 V), with a significant safe working space and unparalleled electrothermal conversion efficiency. CNF content and carbonization temperature directly affect the electrical conductivity and electrothermal properties of CNT/CNF composites. The content and carbonization temperature of carbon nanotubes can be adjusted to meet the requirements. CNT/CNF can drive low-voltage LED lights to light up in a closed-loop circuit, and can de-ice in a very short time.
In summary, the prepared CNT/CNF has excellent performance and broad application prospects in electrical conductivity and electrothermal.
