Tests And Simulation On Controllable Phase-change Characteristics Of Oversaturated Sodium Acetate Trihydrate Solution And The Coupling Solar Hot Water System

The energy demand has been increasing rapidly with the continuous development of human economy.The phase-change energy storage technology can balance the paradox between enery demand and supply in time and space,therefore it can improve the energy efficiency.This paper aims at investigating the supercoiling characteristics of the oversaturated sodium acetate trihydrate solution and developing a new triggering method using the electrode.Besides,the charging and discharging processes of the oversaturated sodium acetate trihydrate solution are also analyszed in detail.Firstly,the thermophysical properties of the oversaturated sodium acetate trihydrate solution are measured using the Differential Scanning Calorimetry and the Chargingdischarging Test.The influencing factors of the supercooling and phase separation phenomenon for the oversaturated sodium acetate trihydrate solution are determined through a comprehensive experimental investigation.The phase seperation problem could be effectively solved by adding Carboxymethyl Cellulose(2% w.t.)and additional water into the oversaturated sodium acetate trihydrate solution.However,the experimental results indicates that the addition of Carboxymethyl Cellulose deteriorates the stable supercooling of the oversaturated sodium acetate trihydrate solution.Therefore,the addition of pure water in the the oversaturated sodium acetate trihydrate solution is adopted in this paper to prevent the phase separation.The mass concentration of the final oversaturated sodium acetate trihydrate solution is 55%.Secondly,a novel triggering method of the oversaturated sodium acetate trihydrate solution is developed using electrodes.The mechanism of the electrical nucleation of the oversaturated sodium acetate trihydrate solution is analyzed.The test results shows that the nucleation of the oversaturated sodium acetate trihydrate solution could be effectively triggered by the electrode.The electrodes used in this paper are made of silver electrodes,sliver-plating electrodes and copper electrodes.Amonst the electrodes above,the silver electrodes demonstrats the best triggering performance.Besides,the effects of electrode geometries and voltages on the trigerring performance are also investigated.Through a comprehensive investigation,the optimized electrode geometry and voltage are 12 mm in diameter and 11.8 V respectively.Finally,the design of the heat storage system with phase change materials is conducted for domestic use.A two-dimensional physical model of the heat storage system with phase change materials is proposed to investigate the charging and discharging characteristics.The mesh and time step used in the simulation model are 34253 and 1 s,respectively.The effects of the inlet flow rates,water temperature and heat conductivity of the phase change material on the charging and discharging characteristics are investigated numerically.The simulation results indicated that when the inlet velocity slows down and the thermal conductivity of phase change material increases,the temperature of outlet becomes higher.