Preparation Of Paraffin/Nano-SiO₂ Composite Phase Change Material And Its Performance Of Electronic Thermal Protection

Under the high ambient temperature conditions, the performance degradation of electronic devices is very easy to occur. In order to make the electronic equipment functioning normally under the extremely high temperature conductions, engineers need to take protection measures. By using phase change materials（PCM） is one of the promising directions to protect electronic devices under high ambient temperature. Through the phase transition processes of PCMs, the protection system can not only maintain a constant temperature of electronic components, but also can be capable of effectively improving the thermal endurance performance and extending the operational lives of electronic devices.In this paper, three grades of nano silicon dioxide（nano-SiO₂）, NS1, NS2 and NS3, were mixed into paraffin to prepare three kinds of nanocomposites as novel insulation materials. Investigations by means of scanning electron micrographs（SEM）, differential scanning calorimeter（DSC） and thermogravimetric analysis（TG） were devoted to studying the structure and thermo-physical property characterization of composites. Experimental results show that the composites particles seem to be much bigger than that of nano-SiO₂ particles. The latent heat of the composites gradually decline with the increase of nano-SiO₂ pore size. The initial decomposition temperature and ultimate decomposition temperature of the composites clearly increase compared with that of paraffin, and the increase is more obvious with the decrease of nano-SiO₂ pore size. To study the thermal stability of the composites, heat storage/retrieval experiments are conducted. Experimental results reveal that the discrepancies of the thermo-physical parameters of the composites including phase change temperature and latent heat before and after thermal cycles are minor, and the TG curves are consistent, and the heat resistance of composites is better with the decrease of nano-SiO₂ pore size. Thus, it confirms that NS1 with the smaller pore size is the best matrix by comparing the latent heat, the performance of heat resistance and thermal stability of the three kinds of nanocomposites. By using NS1 as the supporting material of paraffin enhances the thermal insulation ability of NS1P（75wt.%） composite, and the thermal conductivity of this composite has 36.8% reduction compared with paraffin.For the purpose of investigating the thermal protection effect of NS1P（75wt.%） composite PCM, we designed temperature controlling box by simulating the application system for thermal protection of electronic devices and set up the model for testing the thermal protection effect, conducting theoretical analysis based on numerical simulation. The experimental results reveal that, when the ambient temperature outside box is 150 oC, the thermal protection time of NS1P（75wt.%） composite, which is the time, when the temperature in the central of the temperature controlling box reaches 100 oC, increases as 21.8%, 75.6%, 82.6% and 110.4% compared with that of 90 wt.% paraffin/EG composite, NS1, thermal insulation cotton and air. Besides, the thermal protection declines with the increase of the ambient temperature, but the declining of change gradually decreases. The Fluent software was used to simulate the thermal protection process of the system. The simulative temperature changing trend in the central of the test unit is consistent with that of experiments, but the simulative thermal protection time values are lower than the experimental data. And the error between the simulative values and experimental data of thermal protection time of NS1 P composite gradually decrease with the increase of ambient temperature. Temperature contours on the section of system center showe that the phase change of composite firstly occurres in the corner areas of the unit compared with other areas.