Thermal Properties And Temperature Control Characteristics Of Composite Phase Change Material Based On Modified Boron Nitride Porous Media

With the advent of 5th generation,electronic devices are developing towards miniaturization and integration,which will lead to a sudden rise in the temperature of internal components of electronic devices.The increase of heat flux seriously restricts the safe and stable operation of electronic devices and shortens their life span.Therefore,it is urgent to have strong temperature control measures for thermal management.Three-dimensional porous skeleton composite phase change material gives full play to the high thermal conductivity of porous skeleton and phase change characteristics of phase change material,and the porous skeleton as the carrier of phase change material,can effectively prevent liquid phase leakage,achieve good encapsulation,these significant advantages make it has a good thermal management for electronic devices.In this thesis,hexagonal boron nitride with good thermal conductivity was used as raw material to prepare modified boron nitride nanocrystals and modified boron nitride nanosheets/lauric acid-sodium sulfate composite phase change material.The thermal properties of modified boron nitride nanosheets and composite phase change material were studied and applied in the thermal management of electronic devices.The main research contents are as follows:（1）Peel and modify hexagonal boron nitride with hot oxygen treatment combined with isopropyl alcohol solution oil bath stirring,ultrasonic and other methods.By controlling heat treatment temperature,time,isopropyl alcohol solution density and reaction time,flake boron nitride nanosheets with good hydrophilicity and high yield were successfully prepared.The prepared samples were characterized by transmission scanning electron microscopy（FSEM）,Fourier transform infrared spectroscopy（FT-IR）,X-ray diffraction（XRD）and thermal conductivity tester.The results show that the layer of hexagonal boron nitride is obviously thinner,the thermal conductivity of the modified boron nitride nanosheets is 1.338 W·m^-1·K^-1,which is 95%higher than that of the hexagonal boron nitride raw material,and the surface of the boron nitride is successfully grafted with oxygen-containing functional groups,which effectively improves the dispersion and stability of the suspension.（2）Porous skeleton and modified boron nitride nanosheets/lauric acid-sodium sulfate composite phase change materials were prepared by freeze-drying method and vacuum impregnation method,respectively.The effects of sodium sulfate addition on the rheological properties of suspension,pore structure of porous skeleton,microstructure,chemical structure,leakage rate,stability and related thermal properties of composite phase change materials were studied.The results show that the prepared suspension exhibits shear thinning behavior,and the rheological behavior is similar to that of pseudoplastic fluid.The porosity of porous skeleton increases first and then decreases with the increase of sodium sulfate content.When the sodium sulfate content is 5 wt.%,the porosity can reach 94%,and the pore structure is the most excellent.Considering the thermal properties of the composite phase change material,when the addition amount of sodium sulfate is 5 wt.%,the composite phase change material has the most excellent phase change latent heat and thermal conductivity,which are 143.14J·g^-1 and 0.744 W·m^-1·K^-1,respectively,the leakage rate is 1.89%,which is 26.17%lower than that of the sample without sodium sulfate.The DSC thermal cycle test of the composite phase change material was carried out.The results showed that the phase change curves before and after the cycle were highly coincident,indicating that the prepared composite phase change material has good thermal stability.（3）An experimental platform for thermal management of electronic devices was built to explore the thermal management effect of composite phase change materials on electronic devices.The thermal management effects of constant heating power,type of heat dissipation medium,mass of heat dissipation medium and ambient temperature on electronic devices are studied.At the same time,the thermal shock resistance of composite phase change materials under periodic and intermittent conditions was studied.The results show that the temperature of electronic devices controlled by composite phase change materials is the lowest under both constant and periodic and intermittent conditions.When the constant heating power is 10 W,the ambient temperature is 20°C,and the composite phase change material is 6 g,compared with natural convection heat dissipation and radiator heat dissipation,the time for electronic devices to reach heat balance is prolonged by 887.8%and 222.1%,respectively.When the high/low power is 5-10 W,the test chip temperature is 80.2°C,which is 12.1%and4.0%lower than that of natural convection heat dissipation and heat sink heat dissipation,respectively.On the whole,the heat dissipation of composite phase change materials achieves good temperature control of the chip,which is conducive to enhancing the thermal shock resistance of electronic devices and ensure the safe and stable operation of the electronic devices during the working process.This thesis has 50 figures,10 tables and 116 references.