Study On The Flame Retardancy And Thermal Properties Of Carbon Nanotubes Composite Phase Change Materials And Its Application

The technology of building energy conservation has become important issues of building materials fields. The phase change energy storage technology is becoming one significant way to improve energy efficiency.Because of the low heat transfer and bad thermal stability performance of organic phase change material(PCM), the paper prepared carbon nanotubes-paraffin composite PM, which have better heat storage performance and thermal stability, then prepared the SiO2@MWNTs/paraffin/OMMT ternary composite PCM with good flame retardant properties by mixing carbon nanotubes-paraffin composite PCM with organic montmorillonite(OMMT). The ternary PCM can well be applied to the cement matrix.The carbon nanotubes have excellent heat conduction performance, but they can entwist each other because of the large surface energy when added to the PCM, that decreases the dispersion and heat conduction performance of PCM. Therefore, the carbon nanotubes were modified by the method of that wrapping a layer of silicon dioxide on the surface. The specific surface area and pore size tester was used to contrast the specific surface area of modified and unmodified carbon nanotubes.The research show silica single bonds were introduced on the surface of carbon nanotube successfully. The thermal conductivity of carbon nanotubes in paraffin can be further improved. The specific surface area of modified carbon nanotubes decreased significantly, and the dispersion in paraffin wax had been well improved.The effect of different diameter and content of modified carbon nanotubes on the phase transition temperature and latent heat of paraffin was studied. The addition of carbon nanotubes decreased the phase change temperature, peak temperature and latent heat of paraffin. The latent heat of paraffin decreased more with the diameter of carbon nanotubes becoming smaller. The latent heat of paraffin also decreased with the increase of carbon nanotubes. The addition of carbon nanometer increased the initial and ultimate decomposition temperature of paraffin which increased with the increase of carbon nanotubes.The SiO2@MWNTs/paraffin/OMMT composite PCM had better flame retardant properties, and the addition of carbon nanotubes can promote the formation of carbon layer of OMMT, and make the structure of carbon layer be more dense. So the thermal stability and barrier properties were increased.The article carried on the dynamic analysis about the heat transfer process of carbon nanotubes based composite PCM by the numerical analysis software of Fluent and the influence of natural convection was considered. The heat transfer process of binary (paraffin/OMMT) and ternary (SiO2@MWNTs/paraffin/OMMT) of composite PCM were compared. The reinforced effect of conductivity of carbon nanotubes on the composite PCM was analyzed. The results show that the melting time of composite PCM which considering the natural convection advance 1599s. Because the effect of natural convection on heat transfer occupied a certain proportion, the natural convection can not be ignored. And the PCM can accelerate the melting rate under the influence of natural convection. The melting and solidification time of the composite PCM containing 3wt% carbon nanotubes was respectively reduced by 15% and 22% compared with the binary composite PCM. The natural convection had much effect in the melting process and the main effect was heat conduction in the solidification process.The carbon nanotubes based composite PCM were added to the cement to make of thermal storage cement paste. The effect of binary and ternary composite PCM on the mechanical properties, pore volume, heat transfer performance and pore size distribution of cement was studied. The results show that the addition of composite PCM decreased the compressive strength and density of cement paste. The pore width shifted to the large direction. The carbon nanotubes in ternary composite PCM can reduce the pore volume and improve the strength and the heat transfer performance of heat storage cement paste.