Abstract:

In order to search for high temperature heat transfer and thermal storage materials for solar thermal utilization, the phase diagram calculation method with branchs/regions separation was proposed, and two ternary eutectic mixtures of NaCl-CaCl₂-KCl and KCl-CaCl₂-MgCl₂ were designed. Based on the normal solution model, the phase diagrams of five boundary systems NaCl-CaCl₂,CaCl₂-MgCl₂,KCl-NaCl,KCl-CaCl₂, and KCl-MgCl₂ of the above two ternary systems were calculated with different interaction coefficients of different branches, and the complex phase diagrams containing compounds can be calculated by using the normal solution model. The calculated complex phase diagrams of KCl-CaCl₂, KCl-MgCl₂ systems and the other three systems without compounds were in good agreement with the experimental phase diagrams. Then, the phase diagrams of the ternary systems were calculated by sub region method based on the different interaction coefficients from the five boundary systems, and five new eutectic points of the ternary systems were predicted to guide the preparation of molten salt materials. The lowest eutectic point was verified by differential scanning calorimetry, and the lower limit of molten salt working temperature was determined. The working temperature range was determined by mass loss method. The results show that sodium potassium calcium and potassium magnesium calcium chloride molten salts can operate stably at 550—850℃ and 480—700℃, and can be used as high-temperature heat transfer and heat storage fluids.

Key words: solar energy, chloride molten salt, phase equilibrium, interaction coefficient, phase diagram, thermal stability

摘要：

为寻求太阳能热利用高温传热储热材料，以盐湖资源为原料，提出分支/分区相图计算方法，设计NaCl-CaCl₂-KCl和KCl-CaCl₂-MgCl₂熔盐传热储热材料。基于正规溶液模型，以不同分支不同相互作用系数，计算了5个边界体系相图，实现用正规溶液模型计算含化合物体系复杂相图。含化合物KCl-CaCl₂和KCl-MgCl₂体系及3个不含化合物二元体系的计算相图与实验相图十分吻合。以分区域方法计算三元体系相图，预测出5个低共熔点来指导熔盐制备。采用差示扫描量热法测试并验证熔盐最低共熔点，确定其工作温度下限；以质量损失实验，确定其工作温度上限。结果表明，钠钾钙和钾镁钙氯化物熔盐能在550~850℃和480~700℃内稳定运行，可用作高温传热储热流体。

关键词: 太阳能, 氯化物熔盐, 相平衡, 相互作用系数, 相图, 热稳定性