Lattice Boltzmann simulation of the melting enhancement of composite phase change material with highly conductive additives - Effect of discrete particulate phase and continuous conductive network

Abstract

The melting process of paraffin-aluminum composite PCM in a 2D enclosure is numerically investigated by means of an enthalpy-based lattice Boltzmann method. The aluminum is deployed in discrete particles with size around 100 μm and the continuous fibrous network in the composite PCM, respectively. The effects of equivalent particle diameter, the volume fraction of aluminum additives as well as the local structural rearrangement are systematically investigated. The results demonstrate that the appending of discrete aluminum particles at a low volume fraction (ϕ ≤ 0.2 in this work) even has a negative effect on the melting process, because of the inhibition of the natural convection. By concentrating the particles in either back and top area, the melting performance could be slightly promoted. However, the improvement is very limited. Instead, it is more effective to utilize the continuous conductive fibrous network structure to accelerate the melting, which is suggested to be bespread over the entire PCM with larger local space in the direction of temperature gradient. Furthermore, it is discovered that the critical melting time reduces exponentially with the increase of fiber volume fraction. This work gives a comprehensive understanding of the differences between the discrete particles and continuous structures in the heat transfer enhancement of composite PCM, and offers an optimization strategy in the fabrication of fiber/foam structures.