石墨烯纳米流体相变材料蓄冷特性的数值模拟

Numerical simulation of solidification characteristics of graphene nanofluid as phase change material

鉴于石墨烯高导热性能的特点,将石墨烯纳米流体作为相变材料有望提高蓄冷效率。本文对水基石墨烯纳米流体相变材料的凝固特性进行了数值研究,采用焓-多孔度法追踪固液相界面,分析了石墨烯纳米片质量分数、蓄冷腔体尺寸和几何形状对凝固时间和相界面演化的影响。结果表明,相变材料凝固所需时间随着石墨烯纳米片质量分数的增大显著降低,对于直径为72mm的圆形蓄冷腔体,质量分数为1.2%的石墨烯纳米流体相变材料与去离子水相比凝固时间降低了30.1%,与已有的实验结果相符;随着圆形蓄冷腔体直径减小,石墨烯纳米流体凝固所需时间显著降低,但石墨烯纳米片对凝固的强化作用减弱;在腔体等截面积的情况下,三角形腔体内凝固过程的相界面移动速率明显大于圆形和方形腔体、更有利于促进凝固过程,3种形状腔体内初期凝固都发生在腔体底部、凝固中期相界面形状与腔体本身形状相似、凝固后期相界面趋近于圆形。

Graphene nanofluid is a promising phase change material for improving the efficiency of cool storage. The solidification characteristics of water based graphene nanofluid were numerically investigated;enthalpy-porosity method was adopted to track the solid-liquid interface; the effects of graphene nanosheet mass fraction,cool storage cavity size and geometry on the solidification time and solid-liquid interface evolution were analyzed. The results showed that the solidification time decreased significantly with the increase of graphene nanosheet mass fraction. In a circular cool storage cavity with a diameter of 72 mm,the solidification time for 1.2% graphene nanofluid was 30.1% less than that for the deionized water,which was consistent with the experimental results. With the decrease of circular cavity diameter,the solidification time for graphene nanofluid significantly decreased,but the enhancement effect of thgraphene nanosheet on the solidification was weakened. For the same sectional area,the moving velocity of solid-liquid interface during the solidification in a triangular cavity is larger than that in the circular and square cavities,which indicated that the triangular cavity was more conducive to the promotion of solidification process. For those three types of cavities,the solidification occurred at the bottom of cavity in the initial stage; the solid-liquid interface was similar to the shape of the cavity itself and tended to be circular in the middle and later stages,respectively.