PCM charging process accelerated with combination of optimized triangle fins and nanoparticles

Latent heat thermal energy storage (LHTES) with phase change materials (PCMs) is a promising technique to handle the intermittent issue of renewable energy. However, the major drawback of LHTES is the low thermal conductivity of PCMs. In this work, an enthalpy-based multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) is used to investigate the PCM charging process enhanced by combination of nanoparticles and fins. It is found that the PCM charging rate could be improved with unchanged energy storage capacity by replacing rectangle fins with triangle fins due to the increased heat transfer area between fins and PCMs. The results also indicate that the enhancement of PCM melting speed is more effective by using triangle fins than adding nanoparticles. Besides, at high hot wall temperature, the energy storage efficiency of LHTES even decreases with the increasing nanoparticle volume fraction because of the reduced energy storage capacity and the increased viscosity of PCM which weakens the natural convection. Through an optimization study of triangle fin configuration and arrangement, the long and narrow fins with an appropriate fin distance are preferred for achieving high energy storage efficiency. The use of unequal length triangle fins with a longer one in the bottom region of LHTES cavity is found to be beneficial for ameliorating the NEPCM charging rate. Furthermore, the LHTES cavity with vertical triangle fins heated from the bottom surface is demonstrated to have better energy storage rate than that with horizontal fins heated from the side wall.