Study On Radiative Heat Transfer Performance Of Graphene Thermal Conductive Film In Air Conditioning System

Heat sink is the main task of heat dissipation in air conditioning system,how to improve the heat dissipation capacity without increasing the floor space and at the same time reduce the hot spot temperature of transformer winding is an urgent problem,so it is necessary to carry out research on strengthening the heat dissipation capacity of heat sink.In order to solve the problem of heat dissipation efficiency of air conditioning radiators,this paper uses combustion synthesis to prepare graphene,and pre-selects graphene with relatively outstanding microscopic morphology,organization and thermal properties to make it and polyimide to prepare graphene/polyimide composite thermal conductive film.By analyzing the morphology and characterization of the experimentally prepared graphene,as well as the detailed study of the thermal diffusion coefficient of the graphene/polyimide composite thermal conductive film,the heat dissipation effect of the thermal conductive film on the air conditioner radiator was analyzed.The graphene synthesis was divided into three parts.Firstly,graphene was prepared by combustion synthesis using different ratios of magnesium powder and calcium carbonate and its morphology,structure and thernal properties were analyzed.The results showed that graphene with a 1:2 ratio of reactants had the best overall structural and thermal properties,with a thermal conductivity of 0.2699 W/（m·K）at 350C and 0.2584 W/（m·K）at 227℃.Next,graphene was prepared using three typical sugars,namely glucose,sucrose and starch,as carbon sources,and the results showed that the thermal conductivity of graphene reached 0.3555W/（m·K）when the carbon source was glucose,which was much higher than that of graphene made from the other two carbon sources under the same conditions.Finally,the nitrogen-doped graphene was prepared by using carbamide as the nitrogen source and selecting the optimal product with a magnesium/calcium carbonate ratio of 1:2.The thermal conductivity of this nitrogen-doped graphene was 0.2982 W/（m·K）at 35℃ when the carbamide addition was 14g,and 0.2952 W/（m·K）at 35℃ when the nitrogen content was 8g.The thermal conductivity decreased with the increase of temperature and the larger the nitrogen content.During the preparation of composite films,it was found that the thermal diffusion coefficient and thermal conductivity of the polyimide films obtained by adding graphene to the polyamide acid solution were increased,and the thermal diffusion coefficient was directly proportional to the change of graphene content,and the thermal diffusion coefficient of the polyimide films increased substantially when the graphene addition was 0.5 wt%.With the increase of thermal diffusion coefficient and thermal conductivity of graphene-polyimide composite film,the total thermal resistance of sheet heat sink in air conditioning heat sink system is greatly reduced and the heat dissipation capacity is improved.The enhanced heat dissipation capability is of great significance for the development of fields such as refrigeration and electronics industries.