Study On Energy Storage And Supercooling Properties Of Phase Change Materials Used In Mesothermal Solar Collector Heat System

With the development of our economy, the material and cultural standard of living are improved continually, so the demand of energy is larger and larger. However, the normal energy is decreasing day by day such as coal, oil, natural gas and so on. Therefore, it is important to empolder and utilize the renewable energy. In all renewable energy, solar energy is the clean energy that is remarkable, mostly researched and used widely. But the density of solar radiation energy reached the earth is low, and is influenced by the alternation of geographic position, day and night and the season. And it is also restricted by the weather variations. In order to provide the continous and stable energy for production and living, the energy storage material is needed to storage the superfluous solar energy, and to release the energy when the solar energy is shortage. As the phase change material can meet this demand, so the performance steady phase change material is researched for heat technology of solar energy.Sodium acetate trihydrate has proper melting point temperature, high latent heat of fusion, moderate costs, relatively high thermal conductivity, little toxicity and no peculiar smell. It is attractive material during the hydrated salts. But it exists serious supercooling and phase segregation phenomenas. The degree of supercooling is even higher than twenties. These phenomenas limit the practical use of sodium acetate trihydrate all the time. So some research works were done on the supercooling and cycle stability of sodium acetate trihydrate system through the experiments this paper. The result is that the sodium acetate trihydrate systems of adding 3% carboxy methyl cellulose as thickening agent, adding 0.5% sodium phosphate, sodium silicate and sodium borate as nucleating agents respectively can reduce the degree of supercooling and improve the circular performance. This paper tests and gains the XRD graphs and the datum of solid special heat of sodium acetate trihydrate systems at each cycle, then do some analysis of them. And the principle of phase transformation is used to explain the reason that the performance of sodium acetate trihydrate system decays with the cycle increase.There are lots of excellences of the fatty acid and paraffine, such as congruent melting, nearly no supercooling phenomena, low vapour pressure, no toxicity, without corrosion to metalware, good physicochemical stability and so on. So this paper has chosen stearic acid, palmitic acid, myristic acid and paraffine with suitable melting point and melting latent heat, to research the cycle-performance of them. The datum of solid and liquid special heat of each material at different cycles were obtained and analysed respecttively. The change of special heat was explained by analyzing the crystal structure. Through analyzing the XRD graphs of stearic acid, palmitic acid and myristic acid, it points out the reason that the circular performance of these three PCMs is stable. So stearic acid, palmitic acid and myristic acid can use as phase change materials for solar energy heat utilization. And the circular performance of paraffine is also stable. But the melting point and melting latent heat are influenced when paraffine has low hydrocarbon.