Numerical investigation on improving the heat storage and transfer performance of ceramic /D-mannitol composite phase change materials by bionic graded pores and nanoparticle additives

To speed up the thermal response rate of the latent heat storage system, this research draws on the ideas of bionics and proposes two methods to enhance the performance of heat storage and heat transfer during phase change process. First, a biomimetic, double-gradient porous ceramic was applied to assemble phase change material (PCM) D-mannitol. The optimized gradient pore structure ensures that the composite possesses higher effective thermal conductivity, and better uniformity of phase interface evolution, with reasonable heat storage density. Numerical simulation predicts a 226 % increase in effective thermal conductivity comparing with the pure D-mannitol. Then, two kinds of carbon-based nanoparticles were added to further reinforce the heat transfer performance. Results found that graphite nanoparticles provide the most significant enhancement in the effective thermal conductivity of the composite material under the premise of ensuring a higher heat storage density. In conclusion, the effective thermal conductivity of the final composite achieves 3.33-fold increase due to the collaboration of the double gradient pore framework and the additive graphite nanoparticles. Accordingly, the overall heat transfer rate could be raised by 4.2 times, comparing with the pure PCM sample. This work demonstrates that the bidirectional gradient pore skeleton has significant advantages in heat storage and transfer over the single pore and unidirectional gradient pore.