A comparative study of PCM melting process in a heat pipe-assisted LHTES unit enhanced with nanoparticles and metal foams by immersed boundary-lattice Boltzmann method at pore-scale

Latent heat thermal energy storage (LHTES) has attracted lots of attention due to its nearly constant working temperature and large thermal energy storage density. However, the thermal conductivity of phase change materials (PCMs) is usually low which impedes the heat transfer efficiency in the LHTES system. Adding high thermal conductivity nanoparticles or metal foams are the two common approaches to enhance the thermal performance of the PCMs. In the current work, the PCM melting performance in a heat pipe-assisted LHTES unit enhanced by nanoparticle-metal foam combination is numerically investigated by immersed boundary-lattice Boltzmann method (IB-LBM) at pore scale. The microstructure of metal foam is reconstructed using the quartet structure generation set (QSGS). The PCM melting performance in LHTES is studied in terms of porosity and pore size of metal foams, volume fraction of nanoparticles, and radius of heat pipe. A comparative study is carried out to illustrate the effectiveness of enhancing PCM melting performance with different combinations of nanoparticles and metal foams. The results indicate that there exist the optimum metal foam porosity and heat pipe radius for the energy storage efficiency in the LHTES unit. Besides, it is found that using metal foams is more effective than adding nanoparticles for the improvement of PCM heat transfer capability.