Investigation On The Thermal Performance Of Composite Materials Based On Filler Filling

With the continuous development of society,energy and environmental problems are increasingly becoming the constraints of social and economic development.Thermal energy storage is an effective way to improve energy efficiency and save energy,which is of great significance in reducing energy demand and environmental degradation.As an important way of heat storage and heat storage,phase change energy storage technology is considered to be one of the most potential energy storage mode in twenty-first Century for its advantages of high energy storage density,storage temperature,storage stability of small size compared with other traditional way.High thermal conductive fillers can effectively make up the defects of poor thermal conductivity in the process of energy storage of phase change materials.In this paper,the thermal conductivity of composite materials filled with different artificial fillers and artificial cylindrical / short fiber filler materials is studied respectively.The effective thermal conductivity of composites such as volume content,thermal conductivity ratio,contact resistance and so on are revealed.The effective correlation coefficient of the effective thermal conductivity of composite materials can be used to predict the effective thermal conductivity of composite materials packing with artificial fillers or short fiber fillers.The main research contents and conclusions are as follows:(1)The numerical model of composite material filled with artificial shape filler was established to investigate the thermal performance of composite materials packing with different artificial fillers.The effects of volume fraction,thermal conductivity ratio and contact resistance on the effective thermal conductivity of composite materials were studied.The results show that the effective thermal conductivity of the composites decreases with the increase of the contact resistance,and the decrease rate decreases gradually to the level.Different shapes of fillers have different sensitivity to thermal contact resistance,and the circular and square fillers have the greatest influence on the thermal contact resistance.The thermal contact resistance of different shapes of fillers is different,and the thermal conductivity of the composites filled with flake filler is better than that of powder filler.The effective thermal conductivity of the composites filled with rectangular filler with small aspect ratio is the largest,and the circular and square fillers are the smallest when the volume fraction,thermal conductivity coefficient and thermal contact resistance are considered.The filler-filled composite material with a long channel in the heat flow direction has the highest effective thermal conductivity,which is also the direction of the optimization of the packing shape.(2)A numerical model is established to investigate the influence of the volume fraction,thermal conductivity ratio and aspect ratio of short fiber fillers or artificial cylindrical fillers on the effective thermal conductivity of composite materials.The results show that the effective thermal conductivity of the composites increases linearly with the increase of the volume fraction when the aspect ratio of the filler,and this trend becomes nonlinear after the ratio of length to diameter increases to a certain extent.When the volume content of the filler is small,the aspect ratio has a limited effect on the effective thermal conductivity of the composite.The effective thermal conductivity of the composite materials increases with the increase of the thermal conductivity ratio when the thermal conductivity between the filler and the matrix material is in the range of 1 to 100.When the thermal conductivity ratio between the filler and the matrix material reaches 100,the effective thermal conductivity of the composite is stable,and the thermal conductivity of the filler is not affected by the thermal conductivity of the composite.The effective thermal conductivity of the composites decreases slowly with the increase of the aspect ratio when the aspect ratio of the filler is small,and the effective thermal conductivity of the composites grows faster and faster when the aspect ratio reaches a certain degree.(3)By using the method of non-linear regression,the effective thermal conductivity of the composite material packing with different artificial shape fillers,the effective thermal conductivity of the composite material packing with fiber fillers or artificial cylindrical fillers are respectively obtained and the corresponding effective thermal conductivity is predicted.The new correlations are verified by literature data or experimental method.The effective thermal conductivity coefficient of the composites can be used to predict the effective thermal conductivity of the composites,and the application range of the correlations are given.