| With the development of my country’s goal of "2030 carbon peak and 2060 carbon neutrality",natural gas is an important transition in the transition to renewable energy as a low-carbon and clean fossil energy.Most of the current natural gas boilers use condensing boilers to improve the overall thermal efficiency of the system.However,the accuracy of the evaluation method for boiler thermal performance testing needs to be improved.In order to improve the accuracy of boiler performance test and evaluation,NBT47066-2018 "Condensing Boiler Thermal Performance Test Method" proposes a method to accurately measure the temperature and humidity of condensing flue gas when using the inverse balance method to evaluate the energy efficiency of condensing boilers.The heating section solves the influence of condensed liquid droplets on the sampling flue gas.However,due to the safety voltage and heating power control of the heating cable,the entire sampling gun is too long and the auxiliary power supply makes the entire equipment too large.Therefore,it is necessary to develop high-efficiency heat tracing materials to simplify the structure of the sampling gun and improve the practicability of the sampling gun application.In this paper,a carbon-based polydimethylsiloxane(PDMS)high-flexibility composite material was prepared in the form of a thin film,and related research was carried out through composite film preparation methods,microstructure characterization,electrothermal performance testing,and thermal conductivity analysis.Using polydimethylsiloxane(PDMS)as the matrix material,carbon nanotubes(CNTs)-graphene(GR)-polydimethylsiloxane(PDMS)composite film was prepared by a combination of vacuum filtration and spin coating.The scanning electron microscopy(SEM)was used to analyze the influence mechanism of the surface and cross-sectional micromorphology of the composite film on its structure and electrothermal performance.The temperature field distribution recorded by the infrared thermal imager and the output dynamic temperature curve were used to analyze the resistance,stable temperature,heating rate and electrothermal stability,etc.Thermogravimetric analyzer were used to explore the high-temperature thermal stability and decomposition rules of the composite film.The results show that the synergistic effect of graphene and carbon nanotubes can build a more complete conductive network.The temperature of the composite film is linearly positively correlated with the applied voltage,and the composite film with CNT:GR=2:1 has the lowest resistance of 15Ω,the temperature rises to a stable temperature of 260°C within 30 seconds under 10 V voltage,and it will not cause decomposition and plastic deformation after repeated use.In addition,using an alternating electric field to orient carbon nanotubes to enhance their electrothermal performance,the orientation of carbon nanotubes in the composite film was analyzed by Raman test(Raman)and X-ray diffraction test(XRD),and the orientation composite film was compared and analyzed electrothermal performance.Representative volumetric element thermal conductivity simulations were performed to determine the influence of directional carbon nanotubes on the thermal conductivity of composite films.The dispersion and order of carbon nanotubes after electric field orientation are improved.The insulating polymer layer between carbon nanotubes is reduced,and the increase of conductive contact points increases the heating rate of the composite film by about 1.2 times.The scattering of lattice waves is reduced after orientation,and the thermal conductivity of the composite film is also improved.The flexible composite film with excellent electrothermal performance prepared in this study can be applied to the sampling gun to achieve rapid heat tracing at low voltage,simplify the structure of the sampling gun,and assist the accurate measurement of energy efficiency evaluation of condensing boiler. |
