Study On Preparation And Properties Of Expanded Graphite/Paraffin Composite Phase Change Heat Storage Materials

The phase change heat storage system is a latent heat storage which absorbs or releases latent heat when the phase of material is changing. And the system’s temperature is approximately constant in the process of heat transfer. The performance of phase change materials is the key to the thermal storage capacity of the system.Composite phase change thermal storage material is prepared by phase change material and base material. At present, the phase change heat storage materials are widely used in the fields of solar energy storage, temperature control of electronic devices, "peak shaving and valley" in power, storage battery thermal management system and so on.Therefore, the heat storage technology has become an important technology to improve the utilization rate of energy, and it has important significance to study the composite phase change heat storage material.In this paper, paraffin, which phase transition temperature is 52~54℃,was used as phase change material, and the expanded graphite was used as supporting material. And the expanded graphite/paraffin composite phase change heat storage material was prepared by melt mixing method. This paper detailed introduced selection method of phase change materials and support materials; Sample preparation process of concrete and the preparation conditions of expanded graphite through experiments were introduced. The internal structure of expanded graphite was observed by the SEM, and phase change of the volume expansion ratio of paraffin wax and density were measured;The phase and microstructure of the samples were analyzed by the XRD and the SEM;The phase change latent heat of samples were the analyzed by the DSC; The effect of the content of expanded graphite on the properties of the samples was studied by using the samples in the thermal cycling test. According to the volume expansion rate changesand weightless conditions of the sample were tested in the thermal cycling experiment.The results showed that expanded graphite puffing temperature was 900 ℃,expansion volume the biggest and internal holes were rich. There were no new substances in the composite materials, and the chemical stability were good by the XRD test. When the content of the expanded graphite of non-shape stabilized composite phase change materials reached 10%, the phase change latent heat was 137.39 J/g, and the heat storage density was 229.58 J/g. In the process of thermal cycling, the samples had no paraffin effusion, uniform and internal organization structure.. After 30 thermal cycle, the weightlessness of the sample rate was 2.4%, the phase change latent heat from 137.39 J/g to 136.82 J/g, a difference of 0.57 J/g. It was found that when the expanded graphite content was 30%, the thermal cycle stability of the sample was good,no paraffin seepage, and volume expansion rate was less than 5%, that was below the volume change rate of paraffin phase change, and almost no weight loss in the process of thermal cycle at the same time after testing thermal cycling performance of composite material.