| Sodium sulfate decahydrate is a phase change material at room temperature,which has the advantages of high energy storage density,low cost,safety,and non-toxicity,and has great application potential in the field of building energy conservation;but its supercooling degree is large,and the phase separation is serious and volatile during the cycle process Water,practical application is limited.The predecessors have developed many new composite phase change materials for sodium sulfate decahydrate,but still,use the traditional DSC method to characterize the heat storage performance based on the latent heat of phase change,and the research on cycle stability stays within 100 times,which is difficult to achieve practical application need.First of all,it aims to solve the problems of the small sample quality of the DSC method,the inability of the T-history method to deal with the non-uniformity of composite materials,and the difficulty in controlling the error of the theoretical correction water-heat exchange method.A water-heat exchange method(hereinafter referred to as "environmentally controlled water-heat exchange method")is proposed to control the ambient temperature in the test chamber to reduce the heat dissipation of the system,and a test system is constructed.Water is used as the heat exchange material to measure the composite phase change material as a whole.Latent heat.The latent heat value test and verification using capric acid showed that the mean deviation of the latent heat value results of 5 independent tests and the DSC results in the previous literature was 1.08%,and the relative deviation was within 1.8%.At the same time,the method can test a larger volume of composite phase change materials,which is closer to the actual engineering application requirements.Then,using the physical barrier effect of the layered expanded vermiculite,the sodium sulfate decahydrate is encapsulated by the film vacuum negative pressure process to prepare a composite phase change material sheet,to inhibit the phase separation of the sodium sulfate decahydrate and prevent the loss of water diffusion.Improve service life.Finally,the performance of the composite phase change material was evaluated using the environmental control water heat exchange method.The results show that the physical barrier of film vacuum negative pressure and layered expanded vermiculite has an obvious restraint effect on sodium sulfate decahydrate,enhances the phase separation inhibition ability,and the latent heat retention effect of the composite phase change material is significantly improved;the water-locking effect of the film seal makes the composite phase change The material remains latent heat-stable late in the cycle.Through the optimization of the ratio research,when the composite phase change material of expanded vermiculite with 50% sodium sulfate decahydrate is added,the supercooling degree is 0.5 o C,the latent heat of the initial phase transition is 108.73 J/g,and the latent heat after 500 phase transition cycles is90.74 J/g,the latent heat retention rate is 83.45%,which is 51.4% higher than that without film vacuum packaging.In addition,it has been found that the thermal conductivity enhancement of expanded graphite can further improve the early phase separation inhibition effect of the composite phase change material.The composite phase change material added with 0.5% expanded graphite has a high latent heat retention rate in the early cycle of the phase change.After 300 cycles,the latent heat value is 108.57 J/g,which is22.12% higher than that of the composite phase change material without thermal conductivity enhancement.The thermal conductivity enhancement effect is weakened due to factors such as the uniformity of graphite dispersion.The overall cycle stability of the composite phase change material is excellent,which greatly improves the effective life of sodium sulfate decahydrate,and has broad application prospects in the fields of building energy conservation. |
PDF Full Text Request