The nano encapsulated phase change materials are of the great energy storage potential in various engineering applications. Since they are new nanomaterials, new models for understanding their thermal behavior and capability are essential. This work aims to investigate the unsteady thermal behavior of Nano-Encapsulated Phase Change Material (NEPCM) suspensions in a cylindrical cavity. The particles contain a Phase Change Material (PCM) core, which can absorb/release a substantial amount of thermal energy upon phase change. The phase change particles are well dispersed in a liquid fluid and freely move along with the fluid. The flow, heat transfer, and the particle phase change were modeled using partial differential equations. A non-dimensional approach was employed to generalize the study. The unsteady charging and discharging behavior of the NEPCM suspension are investigated for the volume fraction of the NEPCM particles, fusion temperature of nanoparticles, Stefan number, and the Rayleigh number. Numerical results show that an increment in the Stefan number, i.e., Ste, can significantly reduce the Nusselt number, i.e., Nu_a, at the charging mode of the system. However, the dependency of the Nu_a at the discharging mode on the Ste is negligible. Also, it was found that the effect of the fusion temperature of the particle’s core (θ_f) on heat transfer depends on the working mode of the system. In the charging mode, using a higher value of θ_f decreases the heat transfer rate. Reversibly, a higher value of θ_f inhibits the Nu_a during discharging state. Furthermore, the results show that for Ra = 10⁶, Ste = 0.2, and θ_f = 0.1, a rise of ϕ from 0 to 0.05 leads in about 1.73 and 1.55 times of improvement in the value of Nu_a for the cases of the melting and solidification of the core of NEPCM particles.

纳米封装的相变材料在各种工程应用中具有巨大的储能潜力。由于它们是新的纳米材料，因此了解其热行为和性能的新模型至关重要。这项工作旨在调查圆柱腔中的纳米封装相变材料（NEPCM）悬浮液的非稳态热行为。粒子包含相变材料（PCM）核，相变时可以吸收/释放大量热能。相变粒子很好地分散在液体流体中，并随流体自由移动。使用偏微分方程对流动，传热和颗粒相变进行建模。采用无量纲方法对研究进行概括。研究了NEPCM悬浮液的非稳态充电和放电行为，包括NEPCM颗粒的体积分数，纳米颗粒的熔化温度，Stefan数和Rayleigh数。数值结果表明，Stefan数增加，即Ste可以在系统的充电模式下显着降低Nusselt数，即Nu _a。但是，Nu _a在放电模式下对Ste的依赖性可以忽略不计。此外，我们发现该颗粒的核心（的熔化温度的影响θ _˚F传热）取决于系统的工作模式。在充电模式中，使用的较高值θ _˚F降低传热速率。可逆地，较高的值θ _˚F抑制努_一个放电状态期间。此外，结果表明，对于Ra  = 10⁶，Ste  = 0 。2，以及θ _˚F  = 0.1，的上升φ从0至0.05的引线在大约1.73和1.55的改进倍的值努_一个用于NEPCM颗粒的芯的熔化和凝固的情况。