Abstract The melting of nano-enhanced phase change materials (NePCM) in differentially-heated rectangular cavities was revisited by employing a novel indirect visualization method, i.e., the thermochromic liquid crystal (TLC) technique, to track the invisible phase interfaces. Detailed natural convective flow and heat transfer during melting were also predicted by numerical simulations based on the enthalpy-porosity method, which were validated by comparing with the TLC observations. Two height-to-width aspect ratios of the cavity, i.e., 0.8 and 1.25, were studied. Based on the observed evolutions of the phase interface, it was shown that natural convection originating from the upper corner nearby the phase interface causes the difference in melting patterns between the upper and lower parts of the cavity. The decelerated melting in the presence of NePCM samples with higher loadings (and hence much greater viscosity) was confirmed intuitively by the more vertical and flatten phase interfaces captured by TLC, indicating that heat conduction becomes the dominant mode of heat transfer during melting as a result of the significantly deteriorated natural convection effect. Moreover, when the cavity becoming more slender, the advantage of increased thermal conductivity could be more sufficiently taken because the shorter characteristic length inherently lowers the contribution of natural convection.

中文翻译：

---

使用热致变色液晶 (TLC) 热成像重新审视纳米增强相变材料 (NePCM) 在差热矩形腔中的熔化热传递

摘要 采用一种新型的间接可视化方法，即热致变色液晶（TLC）技术，跟踪不可见相界面，重新研究了纳米增强相变材料（NePCM）在差热矩形腔中的熔化。熔化过程中详细的自然对流和热传递也通过基于焓孔隙率方法的数值模拟进行预测，并通过与 TLC 观察结果进行比较来验证。研究了空腔的两个高宽比，即 0.8 和 1.25。根据观察到的相界面的演变，表明源自相界面附近上角的自然对流导致腔体上部和下部之间的熔化模式不同。通过 TLC 捕获的更垂直和更平坦的相界面直观地证实了在具有更高负载量（因此粘度更大）的 NePCM 样品存在下的减速熔化，这表明热传导因此成为熔化过程中传热的主要模式自然对流效应显着恶化。此外，当腔体变得更细长时，可以更充分地利用增加的热导率的优势，因为更短的特征长度固有地降低了自然对流的贡献。表明由于自然对流效应显着恶化，热传导成为熔化过程中的主要传热方式。此外，当腔体变得更细长时，可以更充分地利用增加的热导率的优势，因为更短的特征长度固有地降低了自然对流的贡献。表明由于自然对流效应显着恶化，热传导成为熔化过程中的主要传热方式。此外，当腔体变得更细长时，可以更充分地利用增加的热导率的优势，因为更短的特征长度固有地降低了自然对流的贡献。