Thermal Storage Characteristics Of Sodium Trihydrate-based Composite Phase Change Materials For Low-temperature Waste Heat Recovery

In China,low-grade flue gas waste heat resources are abundant and their utilization through thermal storage technology is an important method to achieve energy saving and emission reduction under the current double carbon target.Sodium acetate trihydrate is considered to be one of the most promising heat storage materials due to its high latent heat density per unit and its low price,but its large subcooling,severe phase separation,low thermal conductivity and corrosiveness have seriously affected its application.In this paper,a combination of experimental and numerical simulations was carried out to investigate Sodium acetate trihydrate as an object of study.The research content is as follows.(1)Preparation of composite phase change materials using physico-chemical synergistic method.The behavioural characteristics of the product after the reaction was investigated by the synergistic effect of nucleating agent,thermal conductivity enhancer and physical perturbation method using 275 kJ/kg of sodium acetate trihydrate as the experimental object.The results showed that:a composite phase change material with thermal conductivity and subcooling of 1.2 W/m·k and 2.3℃,respectively,was prepared using a 1.5 wt%DSP nucleating agent,a 1.5 wt%EG thermal conductivity enhancer and physical perturbation,and that it has a high latent heat of 258 kj/kg.(2)Modification of composite phase change materials by a synergistic method of physical perturbation and electrical nucleation.The composite phase change material is used as an experimental object to study the behavioural characteristics of the product after the reaction under the synergistic effect of physical perturbation and direct current.The results showed that:In terms of material modification,the synergistic method not only further reduces the composite phase change material subcooling to 0.2℃,but also increases the phase change platform to 3602 s.At this point,the composite phase change material no longer undergoes phase separation in its long-term molten state and it still has a high latent heat of 255.26 kJ/kg;In terms of physico-chemical reactions,the method is to increase crystallinity by physical modification;In terms of thermal storage performance,the latent heat was only reduced by 2.74 kJ/kg after 100 hot and cold cycles,which is a negligible reduction in latent heat;In terms of encapsulated containers,only 304 stainless steel can co-exist well with composite phase change material for a long time due to the corrosive nature of the solution and the weak primary cell reaction of the solution itself.(3)Study of storage and exothermic changes of composite phase change materials in heat exchanger applications.The effect of changes in heat exchanger process parameters,such as inlet flue gas temperature,velocity,thermal conductivity of the composite phase change material and sealing of the encapsulated vessel,on the melting of the composite phase change material in the heat exchanger was investigated.Conclusions indicate that the greater the temperature and velocity of the inlet flue gas to the heat exchanger,the shorter the time to complete melting of the composite phase change material;In terms of the thermal conductivity of the composite phase change material,the greater the thermal conductivity of the composite phase change material the shorter the complete melting time;In terms of heat exchanger sealing,the better the sealing of the outer wall surface the shorter the complete melting time of the composite phase change material.In summary,this paper provided a new approach and pathway to phase change heat storage through a combination of experiments and simulations for the recovery and utilisation of paroxysmal low temperature waste heat under a dual carbon target.