| Using phase change material(PCM) to store thermal energy during valley electricity and release heat during peak electricity, it can realize peak load shifting, save energy and reduce pollution. Morever, based on the features of high thermal energy storage density, constant temperature and thermal comfort, PCM has wide application prospect in the floor radiant heating. Recently, inorganic hydrated salt such as sodium acetate trihydrate(SAT) has been widely studied due to its advantage of high enthalpy of phase change, excellent thermal conductivity and low price. However, pure SAT has the melten point of 58℃ and the drawbacks of suppercooling degree and phase separation, if directly used in floor heating, the PCM stability can not be guaranteed, and the floor surface temperature exceeds the human body thermal comfort range of 22?28 ℃. Therefore, using SAT as raw material, it is of theoretical significance and practical value to study the phase change materials suitable for floor heating.In this paper, a novel(SAT)/formamide(FA) composite phase change material(CPCM) was prepared by using SAT as phase change matrix, FA as modifier and adding other additives. And the effects of the FA mass fraction, nucleating agent and thickening agent on the phase change enthalpy and the melting temperature of SAT/FA CPCM were systematically discussed. The structure and performance of novel CPCM were characterized by FTIR, XRD, DSC and Hotdisk thermal constant analyzer. The exothermic performance of SAT/FA CPCM was meatured by step cooling curve. It showed that the SAT/FA eutectic mixture could be formed by adding 25% formamide into SAT. The SAT/FA CPCM formed by adding 2% disodium hydrogen phosphate dodecahydrate(DSP) as the nuclear agent and 2% polyvinyl alcohol(PVA) as thickening agent, had a low degree of supercooling(2.67℃), long heat release time(10170 s) and excellent cycling stability.In order to expand the application of composite phase change material in phase change accumulator, it was carried out the research on the heat transfer performance of expanded graphite(EG) enhanced SAT/FA CPCM. And effect of mass fraction of EG on the phase change temperature, the latent heat, the heat transfer coefficient and the life of the cycle was studied. The results of XRD and FT-IR showed that it was just physical mixing without any chemical reaction between SAT/FA eutectic salt and EG. With the increase of EG mass fraction, the thermal conductivity gradually increased, and the melting and crystallization rate was enhanced. In addition, the flowability of the composite material was weakened, and the shape stability was enhanced. According to the step cooling curve in the water bath, it is showed that the supercooling degree decreased and the released heat time reduce with the adding of EG.Choosing SAT/FA CPCM as the research object and the electric heating film as the heating unit, the study on experimentail simulation room of electric floor radiant heating system(EFRHS) was carried out. The temperature change results of EFRHS during the thermal storage and release process showed that the phase change thermal storage was beneficial to reducing the heating rate of the electric heating film, preventing the overheating and prolonging the service life. Under the same electric heating power, taking the heat storage time, the indoor air temperature and floor surface temperature as the starting and stopping point of the electric heating film, the experimental results showed that the last two control schemes could better meet the requirements of human thermal comfort. |
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