Thursday, December 24, 2009

Chinese Researchers Fire Up First Carbon Nanotube Based Heaters-CNT Wires Prove Superior to Traditional Metal Heating Coils



Heaters based on carbon nanotube wires have been developed by Tsinghua University (Beijing City, CN)  researchers and may be developed for the marketplace by Hon Hai Precision Industry Co., Ltd (Tu-Cheng City, TW).

Carbon nanotube wires used in the heating coil prove to be superior in performance and have a longer life than traditional wire heating coils, according to inventors Chen Feng,  Kai Liu,  Ding Wang, Kai-Li Jiang, Chang-Hong Liu Shou-Shan Fan (Beijing City, CN).  In Tsinghua's and Hon Hai's joint U.S. Patent Application 20090314765, the two organizations reveal both hollow and planar carbon nanotube based fabricated. 


The heating elements include carbon nanotube structures. The carbon nanotube structures include a plurality of carbon nanotubes uniformly distributed therein. The carbon nanotubes can be combined by van der Waals attractive force. The carbon nanotube structure can be a substantially pure structure of the carbon nanotubes, with few impurities. The carbon nanotubes can be used to form many different structures and provide a large specific surface area.

The heat capacity per unit area of the carbon nanotube structure can be less than 2.times.10-4 J/m2K. Typically, the heat capacity per unit area of the carbon nanotube structure is less than 1.7.times.10-6 J/m2K. As the heat capacity of the carbon nanotube structure is very low, and the temperature of the heating element  can rise and fall quickly, which makes the heating element have a high heating efficiency and accuracy. 

As the carbon nanotube structure can be substantially pure, the carbon nanotubes are not easily oxidized and the life of the heating element will be relatively long. Further, the carbon nanotubes have a low density, about 1.35 g/cm3, so the heating element is light. As the heat capacity of the carbon nanotube structure is very low, the heating element has a high response heating speed.

As the carbon nanotube has large specific surface area, the carbon nanotube structure with a plurality of carbon nanotubes has large specific surface area. When the specific surface of the carbon nanotube structure is large enough, the carbon nanotube structure is adhesive and can be directly applied to a surface.

A typical heater includes a heating element and at least two electrodes. The heating element is located on the two electrodes. The heating element generates heat when a voltage is applied to it. The heating element is often made of metal such as tungsten. Metals, which have good conductivity, can generate a lot of heat even when a low voltage is applied. However, metals may be easily oxidized, thus the heater element has short life. Furthermore, since metals have a relative high density, metal heating elements are heavy, which limits applications of such a heater. Additionally, metal heating elements are difficult to bend to desired shapes without breaking. 

The carbon nanotube hollow heater includes a hollow supporter, a heating element and at least two electrodes. The least two electrodes electrically connected to the heating element. The hollow supporter defines a hollow space, and the hollow supporter has an inner surface and an outer surface. The heating element is located on the inner surface or the outer surface of the hollow supporter. The heating element comprises at least one carbon nanotube film comprising a plurality of carbon nanotubes, and an angle between a primary alignment direction of the carbon nanotubes and a surface of the carbon nanotube film is 0 degrees to 15 degrees. 

Heaters are configured for generating heat. According to the structures, the heaters can be divided into three types: linear heater, planar heater and hollow heater.

The linear heater has a linear structure, and is a one-dimensional structure. An object to be heated can be wrapped by linear heater when the linear heater is used to heat the object. The linear heater has an advantage of being very small in size and can be used in appropriate applications.

The planar heater has a planar two-dimensional structure. An object to be heated is placed near the planar structure and heated. The planar heater provides a wide planar heating surface and an even heating to an object. The planar heater has been widely used in various applications such as infrared therapeutic instruments, electric heaters, etc.

The hollow heater defines a hollow space therein, and is three-dimensional structure. An object to be heated can be placed in the hollow space in a hollow heater. The hollow heater can apply heat in all directions about an object and will have a high heating efficiency. Hollow heaters have been widely used in various applications.

FIG. 7 is a Scanning Electron Microscope (SEM) image of an untwisted carbon nanotube wire used to form heating coils.





FIG. 8 is a Scanning Electron Microscope (SEM) image of a twisted carbon nanotube wire used to form heating coils for carbon nanotube based heaters.



 
FIG. 9 is an isotropic view of a hollow heater having a carbon nanotube structure.


 

FIG. 14 below  is a flow chart of a method for fabricating the hollow heater






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