球状相变蓄热材料在水箱中的分层特性数值分析与实验

Analysis of the Thermal Stratification Property in Hot Water Tank With Globular PCMs: CFD and Experiment Study

在太阳能光利用过程中,蓄热水箱能作为提高水箱蓄热效率和蓄热能力的关键元件。选用三水合醋酸钠为蓄热材料,搭建蓄热水箱测试平台,并建立水箱的传热流动数值模型,对蓄热水箱释热过程进行模拟,结合实验结果深分析水箱的热分层机理。在水箱初始温度为353.15K,进水温度为278.15K时,研究相变材料在水箱中的不同位置和流量下,从无量纲时间角度测量它们对蓄热水箱温度的影响。采用理查德森数和混合数对不同位置和入口流量的热特性进行了分析,实验结果表明随着蓄热球位置越低、流量越小,混合数和斜温层厚度越小,理查德森数(Ri)越大。相变蓄热球的半衰期(即液化率达到50%)随着进口流量的增加而延长。理查森数的模拟值略大于实验值,而混合数的模拟值略小于实验值。理查森数和混合数实验值和模拟值的均方根误差随着相变蓄热球位置的降低和进水流量的增加而增大。

In the process of solar energy utilization, the thermal storage water tank is the crucial element to improve the thermal efficiency and the capacity of heat storage. In this paper, sodium acetate trihydrate was selected as the latent storage material, the storage tank test platform was designed and constructed. The CFD model of the hot water storage tank was established, and the heat release process of the hot storage tank was simulated, combined with the experimental results to deeply analyze the thermal stratification mechanism of the water tank. Under the conditions of initial water temperature of 353.15 K and inlet water temperature of 278.15 K, their influence on the temperature of the heat storage tank was measured with dimensionless time in different positions of phase change material(PCM) sphere and flow rates. The Richardson number and mixing(MIX) number were used to extensively analyses the thermal characteristics of the heat storage water tank with different position as the variation in flow rates. The results show that the lower the position of the PCM, the smaller the inlet flow rate of the water tank, the MIX number, and thickness of the thermocline layer are smaller, and the Richardson number is larger. The half-life of the PCM sphere(i.e., the liquefaction rate reaches 50 %) is prolonged as the inlet flow rate increases. The simulated values of the Richardson number are slightly higher than the experimental values, while the simulated values of the Mix number are less than the experimental values. The RMSE of Richardson, MIX number, and simulation value increases with the decrease of the position of phase change heat storage sphere and the increase of inlet water flow.