Design And Performance Of Calcium Magnesium Chloride Water-salt System Phase Change Materials

Improving energy utilization,energy saving,emission reduction and sustainable development have become the focus of current industrial production.In the related industries of Qinghai Salt Lake,the by-produced MgCl₂?6H₂O is landfilled because it cannot be used efficiently,resulting in waste of resources and environmental pollution.Phase change materials?PCM?can store or release latent heat during the phase transition process and become an important class of energy storage materials.From the processes of finding new phase change materials,the traditional"one-by-one addition method"has a large workload and high investment,and it is difficult to find the true eutectic point of the system.Based on the abundant magnesium salt resources in Qinghai Salt Lake,this paper predicts the CaCl₂-MgCl₂-H₂O ternary system phase diagram by selecting the appropriate thermodynamic model-BET model and according to the model parameters of the CaCl2-H2O and MgCl2-H2O binary systems.The eutectic point with suitable temperature was found on the phase diagram of the system.At the same time,the thermal property characterization methods of inorganic hydrated salt phase change materials were summarized.And the generation principles and suppression methods of supercooling and phase separation of inorganic hydrated salts are explored.The main conclusions are as follows:?1?The BET model has few calculation parameters,clear physical meaning,and the model parameters are less fluctuated due to temperature,which can be approximated as a constant.It has a good prediction effect for the multiple brine system in the high concentration range,and is the preferred model for predicting the phase diagram of the ternary system CaCl₂-MgCl₂-H₂O;?2?Based on the BET model,two eutectic points with phase transition temperatures of 25.01°C and 21.1°C were found from the phase diagram of the ternary system of CaCl₂-MgCl₂-H₂O,its mass percentage composition is CaCl₂:MgCl₂:H₂O=42.56%:8.73%:48.71%and CaCl₂:MgCl₂:H₂O=28.36%:17.24%:54.4%.?3?By adding nucleating agents and thickeners,the supercooling degree of hydrated salts can be reduced and the phase separation phenomenon can be suppressed,but the latent heat of phase change of the hydrated salt can also be reduced.