| Storing heat using supercooled effect of inorganic salt hydrate phase change materials is an effective means to solve the problems of instability,intermittency and mismatch between supply and demand with solar energy and other renewable energy sources.In this paper,two kinds of salt hydrate phase change materials,sodium acetate trihydrate(SAT)and sodium thiosulfate pentahydrate(STP),were studied experimentally.Firstly,Solid steel balls were applied to hit the surface of a rounded-rectangular thermal storage unit made of stainless steel for solidification activation,and the effects of percussion momentioms and positions on activating solidification of the supercooled sodium acetate trihydrate solution in the units were experimentally investigated based on the measured percussion number and crystallization induction time.The results show that the percussion vibration is an effective method to activate solidification for energy release of this supercooled salt hydrate phase change material.The results also confirmed that the induction time decreases for larger percussion momentum.The induction time is also reduced when the percussion is exerted near the sealing cover or the edge corner of the heat storage unit.In the same percussion position,the percussion effectiveness is a constant.And it is easier to achieve activating solidification for the smaller percussion effectiveness.Further,experiments were performed on two heating systems using thermal storage units filled with supercooled sodium acetate trihydrate,i.e.the hot water floor heating with capillary mat and direct heat release to the room air,respectively.The results show that,with the terminal of eapillary mat,the maximum supply water temperature reaehes 35? with the initial temperature of 25? and the room temperature increases from initial 20.3? to the maximum 25.8?.The room temperature variation is 2.5h later than the water supply temperature.The room temperature could be kept above 25? after the system running for 12h.Also,the temperature difference between the heights of 0.5m and 1.5m in the room is within 0.2?.While the thermal storage units directly release heat to the room air with the same mass of phase change materials,the room temperature could be increased from 20.3OC up to 26.6? with 1.lh shorter than that of the capillary mat terminal.However,the room temperature is kept above 25? for only 4h,and the maximum temperature difference between the heights of 0.5m and 1.5m in the room is 0.7 C.Therefore,the combination heat storage using supercooled SAT and the capillary mat terminal not only meets the room temperature requirement,but also has better thermal comfort.In addition,the physical properties of two kinds of phase change materials,sodium acetate trihydrate(SAT)and sodium thiosulfate pentahydrate(STP),were studied respectively in the experimental bottles and rounded-rectangular thermal storage units.The results show that both SAT and STP could achieve stable supercooling with ambient temperature.For the performance of remitting phase separation,STP is superior than SAT.After repeated experiments,phase separation is not found in STP solution.However,the phase separation of SAT is obvious,and with the increase of cycle times,the phase separation becomes more serious.The mixture system of 1%carboxymethyl cellulose(CMC)and SAT can alleviate the phase separation of this materials,but the supercooled stability of the mixture system is reduced.When the phase change materials were studied in the rounded-rectangular thermal storage units,SAT diffusion rate of solidification is approximately 10mm/s,and the maximum temperature rise rate is 3?/s when the material begins to activate solidification.Comparatively,STP diffusion rate of solidification is 1.1-1.6 mm/s,only 13.5%of the SAT,and the material maximum temperature rise rate is 0.65?/s,only 21.7%of the SAT.The experimental results provide the basis and guidance for the selection of salt hydrate phase change materials. |
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