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以海藻酸钙为壁面,石蜡/高密度聚乙烯定形材料为囊芯的球形相变胶囊为对象,建立了凝固传热过程的相变模型。模型中同时考虑了石蜡的体积变化和空腔分布,并根据囊芯材料的微观结构特征,基于分形理论对其等效导热系数进行了有效表征。采用了显热容法模拟了相变胶囊凝固过程中的传热和相界面位置的移动。模拟显示:考虑相变材料的体积变化对初始阶段的凝固过程几乎没有影响,但此后随着固相率逐渐增加,热传递速率明显减缓;初始空腔率不仅影响了相变传热速率,也降低了单位体积胶囊的相变潜热;越大的胶囊尺寸斯蒂芬数对其完全凝固时间所造成的差异愈加显著。该结果对如何提高相变胶囊的储存量和储存速率具有一定的指导意义。
The phase transition model of the solidification and heat transfer process was established for the spherical phase change capsule with calcium alginate as the wall surface and paraffin / high density polyethylene as the shaping material. In the model, both the volume change and cavity distribution of paraffin were considered simultaneously. Based on the microstructure characteristics of the core material, the equivalent thermal conductivity of the core material was characterized based on the fractal theory. The sensible heat capacity method was used to simulate the heat transfer and phase interface movement during the phase change capsule solidification process. The simulation shows that considering the volume change of the phase change material has little effect on the initial solidification process, the heat transfer rate obviously slows down with the increase of the solid fraction gradually. The initial cavity ratio not only affects the phase transformation heat transfer rate but also Reducing the latent heat of phase change per unit volume of the capsule; the larger the difference between the size of the capsule size and the number of complete coagulation of the Stephen number more significant. The results have some guiding significance on how to improve the storage capacity and storage rate of phase change capsules.