Enhancement of nanoparticle-phase change material melting performance using a sinusoidal heat pipe

Highlights: • An immersed boundary-lattice Boltzmann method for phase change is developed. • A sinusoidal heat pipe is designed for latent heat energy storage unit. • Using heat pipe is more effective than adding nanoparticles for energy storage. • An eccentric sinusoidal heat pipe is recommended for improving energy storage rate. -- Abstract: Thermal energy storage with an assisted-heat pipe has several useful applications in engineering fields. Due to the large latent heat and nearly constant melting temperature, phase change materials become attractive for thermal energy storage applications. Unfortunately, the low thermal conductivities of phase change materials become a significant issue which should be overcome to achieve high energy storage efficiency. In the current work, a novel sinusoidal heat pipe is designed instead of a circular heat pipe in order to accelerate the melting rate of nanoparticle-enhanced phase change material without affecting the thermal energy storage capacity of system. By developing an enthalpy-based immersed boundary-lattice Boltzmann method for the solid-liquid phase change phenomenon, the melting process of nanoparticle-enhanced phase change material with a sinusoidal heat pipe is investigated with respect to different heat pipe temperature, heat pipe undulation number and sinusoidal amplitude, nanoparticle volume fraction, and eccentric location of heat pipe. The results indicate that the energy storage rate of nanoparticle-enhanced phase change material is highly improved by applying a sinusoidal heat pipe because of its enlarged heat transfer area between heat transfer fluid and nanoparticle-enhanced phase change material. Furthermore, through an optimization study, it is found that applying a sinusoidal heat pipe with larger radius is more effective than adding high thermal conductivity nanoparticles into phase change material to enhance the thermal energy storage rate. Besides, the sinusoidal heat pipe with an eccentric location near the bottom of thermal energy storage cavity is highly recommended to realize a faster phase change material melting rate due to the enhanced effect of natural convective heat transfer.