Research On The Heat Storage Properties Of Sn-Bi-Zn-Cu-Pb Alloys As Phase Change Materials In Medium Temperature

The development of heat utilization field promoted the development of medium temperature heat storage system, as the important composition of heat storage system, the heat storage materials would be more and more widespread concerned. Metal and alloys phase change materials (PCMs) had good application prospect because of their large energy storage density, high thermal conductivity, low supercooling degree and good reliability of thermal cycling in the long term, so they played an important role in thermal energy storage field. Based on the metal and alloy used as thermal storage material with high energy storage density, stable performance, thermal conductivity, and the basis of our groups early research on high temperature aluminum alloy PCMs, with the appropriate melting point, this paper selected low melting point alloys as a new kind of medium temperature PCMs, provide a new type medium temperature PCMs with the high energy storage density, stable performance and good thermal conductivity for the heat storage device and system.Structures and properties of these PCMs are studied by EPMA, DSC, XRD and laser thermal constants measuring apparatus. The result showed that the Sn-Zn eutectic alloy had optimistic heat storage performance,its melting point was198℃, latent heat was65.8J/g, density was7.38g/cm3, thermal conductivity was53.4W/(m-K), the unit volume heat storage capacity was485.6J/cm3. Its heat storage capacity was bigger than the NaNO3/KNO3salt, so the thermal performance of Sn-Zn eutectic alloy had a great advantage.The lifetime of PCMs detemines whether they had good value or not, so the stable performance played an important factor. Form the repeated melting solidification thermal cyclings test, with the thermal cycling times increasing, the result showed that phase-change temperature rose, latent heat and thermal conductivity decreased slowly. After500thermal cycles, phase-change temperature increased by2℃, latent heat decreased by1.1J/g and thermal conductivity decreased by2.55W/(m·K). The change of microstructure and thermal physics properties after thermal cyclings showed that Sn-Zn eutectic alloy had good reliability of thermal cycling and could be used as PCMs in the heat storage system. Element and content would impact on the microstructure of the alloy structure and the thermal properties, so joined the different content of Bi, Cu alloy elements into Sn-Zn eutectic alloy and analysed the change of their microstructure and thermal properties. Bi could make Zn-rich phase coarse and a small amount of white Bi phase was appeared. With the content of Bi increasing,the phase-change temperature was reduced. In addition, the latent heat and thermal conductivity of alloys were also reduced. Cu could decrease the srtip Zn-rich phase and produce the black granular Cu5Zn8compounds. With the content of Cu increasing,the latent heat of alloys were decreased, due to Cu5Zng compounds with higher melting temperature and with the accession of the Cu, the generated Cu5Zn8compounds increased, so the effective latent heat decreased under300℃, the phase change temperature and thermal conductivity of alloys were increased.This research showed that the heat storage properties of low melting point alloys was very well, and rvoided more selection of PCMs for medium temperature heat storage application.