Study On Of Sodium Acetate Trihydrate Composites And Its Stability As Phase Change Mateials

Sodium acetate trihydrate?SAT?has frequently proposed as a promising phase change material?PCM?between 50 and 60 degree Celsius owing to its high thermal energy density,high coefficient of heat conductivity and the charactieristic that it can be able to store or release large quantities of energy at constant temperature.In this paper,crystal growth of SAT,heat resistance of nucleation catalysts and thickers,as well as cycling stability of SAT composites were systemationlly studied.In order to prepare SAT composites that have good cycling stability,the following work was done in advance.The crystal growth process and temperature fields during the phase change of sodium acetate trihydrate were visualized using the KH-7700 3D digital microscope and the infrared camera VarioCAM.Meanwhile,the three stages of crystal growth process has been observed.To overcome the supercooling and phase separation of SAT,twelve potential nucleators and three thickers have been evaluated by step cooling curve.Furthermore,the expriments show that disodium hydrogen phosphate dodecahydrate?DSP?is evidently superior to other nucleators.Nonetheless,it was found that DSP wound get deactivation provisionally when heated over 75??This phenomenon could be interpreted by“effective components”model and“heterogeneous adsorption”model.Mechanism of phase separation was elucidated by phase diagram of sodium acetate–water system and XRD analysis.Sodium acetate trihydrate melts incongruently into an aqueous solution containing58 wt%sodium acetate anhydrous.This solution and the anhydrate solid-state sodium acetate are in a state of balance.As the cycle index being increased,Anhydrate solid–state sodium acetate continually settles to the bottom under gravity effect,resulting in a phase separation.According to that mechanism,the effects on phase separation of the presence of attapulgite,hydroxyethyl cellulose?HEC?and carboxymethyl cellulose?CMC?were investigated.Results show that attapulgite is not suitable for controlling phase separation.The infrared spectroscopic analysis?IR?has verified that HEC is of better heat resistance than CMC.In addition,1 wt%Nano-SiO₂ has been discovered experimentally to counteract the adverse effects resulting from 10 wt%extra water that was used to prevent phase separation,thereby relieving“triangle contradiction”among supercooling,phase separation and extra water.Based on the above research,SAT composites containing 2 wt%DSP,2 wt%HEC,1 wt%Nano-SiO₂ and 10 wt%extra water were prepared and tested for 200 thermal cycles.Results indicate that the material has higher latent heat of 232 kJ/kg and better thermal stability.Degree of supercooling and phase change temperature maintained 1.68⁶.75?and56.07⁵7.94?during 200 thermal cycles,respectively.It has been proved that no sodium acetate anhydrous generated by X-Ray Diffraction.