泡沫金属在熔盐相变蓄热中的强化传热特性

Heat transfer enhancement performance in phase change process of molten salt using foam metal

搭建了熔盐蓄热特性实验平台,开展相变蓄热过程传热特性实验研究。建立了蓄热容器二维轴对称、瞬态固液相变数学模型,相变过程模拟采用Solidfication&melting模型,相变区域采用Boussinesq近似,对比了纯硝酸盐蓄热工况和填加泡沫金属后蓄热工况数值模拟结果。采用实验与数值模拟相结合的方法,重点分析了泡沫金属对熔盐蓄热过程的强化传热作用。结果表明,填加泡沫金属能够有效提高熔盐换热速率,泡沫金属孔隙率越小强化蓄热效果越显著。泡沫铜的热导率较高,相对于泡沫镍和泡沫铝有更好的强化传热效果,蓄热速率是纯硝酸盐蓄热的1.6倍。在相变蓄热后期自然对流换热占主导地位,此时泡沫金属会抑制自然对流。同时,填加的泡沫金属越靠近容器中心位置,对自然对流抑制作用越强,蓄热性能越差。

The phase change heat storage technology shows many advantages,such as large energy storage density,low cost and etc.However,the property of low thermal conductivity of the phase change material limits its wide application.As a new heat transfer enhancement material,foam metal has relatively higher thermal conductivity and higher specific area.The molten salt heat storage experiment was carried out and the physical model of phase change thermal storage was constructed.A twodimensional axisymmetric,transient solid-liquid phase transition mathematical model of the thermal storage vessel was established.The phase transition process was simulated using the solidification&melting model,and the phase transition region was based on the Boussinesq approximation.Numerical simulation results of thermal storage conditions of pure nitrate and thermal storage conditions after adding foam metal were compared.The heat transfer enhancement effect with the application of foam metal in the molten salt thermal storage process was analyzed by experiments and numerical simulation.Results showed that foam metal can effectively improve the heat transfer rate of the molten salt.Foam metal with relatively smaller porosity or higher thermal conductivity can generate a better enhanced heat storage effect.In the later stage of the heat storage process,natural convection heat transfer was the main heat transfer mode and foam metal severely inhibited natural convection.Comparing different filling positions of the foam metal,it was found from this paper that the filling position was closer to the center of the container,natural convection was weakened and the corresponding heat storage performance was worse.