Liu Wenwei， Shi Xinlin， Fu Jingwen， Huang Yun

State Key Laboratory of Mesoscience and Process Engineering， Institute of Process Engineering， Chinese Academy of Sciences， Beijing 100190， China； School of Chemical Engineering， University of Chinese Academy of Sciences， Beijing 100049， China

Abstract 

Objective The packed bed with core-shell particles provides an effective approach for improving the release efficiency of high-temperature thermal energy storage systems using phase change materials （PCMs）. However， the comprehensive understanding of the heat transfer mechanisms of composite particles remains unclear， which limits the optimization of packed bed structures. To explore the effects of shell thickness， thermal properties， and packing structure on the melting performance of spherical core-shell composite PCMs， this study performs numerical simulations of the melting processes of single particles and particle beds generated by random packing.

Methods The lattice Boltzmann method with double distribution functions was employed to solve the fluid flow and PCM enthalpy. The simulation domain was set as a square with dimensions of 200 × 200 lattice units. The four boundaries were set as no-slip walls. The left and right walls were set to constant temperatures and ， respectively， while the top and bottom walls were set as adiabatic. The domain was filled with randomly packed particles， where each particle was composed of a PCM core and a shell material with high thermal conductivity. The PCM was selected as NaNO3， and the shell materials included Al， graphite， and multi-wall nanotubes （MWNTs）. Two series of simulations were carried out. The first series involved single-particle melting simulations with a PCM size of lattice units and a dimensionless shell thickness of . The second series involved the melting of random packings with a packing density of .

Results and Discussion For the melting of single core-shell particles， it was found that the complete melting time decreased linearly with increasing shell thickness. This was because the thicker shell enlarged the heat transfer area between the shell and the fluid in the domain. However， the linear slope decreased with the decrease of PCM volume， indicating that the enhancement effect of the shell became more prominent for larger volumes of PCM. Furthermore， the physical properties of the shell material had a significant effect on the melting process. Among the three shell materials considered in this study， graphite exhibited the best performance due to its lower heat capacity， followed by Al and MWNTs. This was because the thermal conductivities of these three shell materials were sufficiently high， so that the thermal resistance inside the shell could be neglected and heat transfer was instantaneous. The thermal energy from the fluid was first transferred to heat the shell， which was determined by its heat capacity. As a result， less thermal energy was required to heat the graphite shell， leading to a faster PCM melting rate under the same thermal input. By artificially tuning the thermal conductivity of the shell material， it was found that the PCM melting was remarkably suppressed when the thermal conductivity of the shell material was reduced to 1/1 000 of the original value. Moreover， the results suggested that the thermal conductivity of the shell material should be at least 10 times higher than that of the PCM， where little improvement was achieved with further increases in thermal conductivity. For the melting of the packed bed， it was observed that the complete melting time decreased exponentially with increasing packing density， which was attributed to the formation of a highly connected network between particle contacts. The packed bed structure formed by random packing was sufficient to achieve an acceptable melting rate， and further increasing the packing density yielded limited benefits.

Conclusion This study provides a systematic numerical investigation of the melting performance of composite PCMs with core-shell structures at the microscopic particle scale， which can be used to guide material design， parameter selection， and packed bed structure optimization. The results demonstrate that adding a high-thermal-conductivity shell can effectively enhance the melting rate of PCMs. However， it reduces the PCM volume， which leads to a decrease in the total heat storage capacity. From the perspective of practical applications， a trade-off needs to be achieved between heat storage capacity and melting rate. Therefore， it is necessary to establish a more comprehensive and integrated evaluation indicator in future studies.

Keywords： phase change material； thermal energy storage； particle； random packing； lattice Boltzmann method

Get Citation:Liu Wenwei， Shi Xinlin， Fu Jingwen， et al. Numerical simulation of melting performance of core-shell composite phase change materials［J］. China Powder Science and Technology， 2026， 32（5）： 1-12.

Received：2026-07-21， Revised： 2026-08-18， Online： 2026-08-31。

Funding： The research was supported by the Coal Major Project (Grant No. 2026ZD1702301) and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA0400102).

CLC No.:O414.13； TK11+4； TB44；

Type Code:A

Serial No.:1008-5548（2026）05-0001-12