A self-actuating internal stirring mechanism to maintain dispersion uniformity in paraffin/carbon nanotube phase change composites

Paraffin-based Phase Change Materials (PCMs) are promising candidates for Thermal Energy Storage (TES) systems, but their low thermal conductivity is often a significant drawback. While the addition of high-conductivity nanoparticles like Carbon Nanotubes (CNTs) can address this, long-term performance can be compromised as CNTs agglomerate and separate from the paraffin matrix over repeated thermal cycles. This degradation is driven by fundamental solidification phenomena such as particle pushing, which leads to a breakdown of the conductive nanoparticle network. To address this, we developed a novel self-actuating internal stirring mechanism that maintains dispersion uniformity without external power. Leveraging the volumetric expansion of the PCM itself (the “wax motor” principle), the device autonomously converts thermal energy into rotational mixing during the melting phase. A Computational Fluid Dynamics (CFD)-optimized Sawtooth impeller was engineered to generate high local shear rates (>140 s −1 ) sufficient to initiate CNT deagglomeration. Experimental validation over 50 thermal cycles demonstrated that the active stirring effectively suppressed phase separation. From the 128.7% initial improvement over pure paraffin, the stirred composite retained ∼90% of its initial thermal conductivity (0.391 W/(m·K)), significantly outperforming the unstirred control which degraded by 26% (0.334 W/(m·K)). This work establishes a successful proof-of-concept for a semi-active stabilization strategy to overcome the long-term reliability barriers in latent heat storage systems.