The Impact of Thermosolutal Convection on Melting Dynamics of Nano-enhanced Phase Change Materials (NePCM)

Abstract

Nanoparticle-Enhanced Phase Change Materials (NePCM) have been a subject of intensive research owing to their potential for enhanced thermo-physical properties. However, their behavior during phase change processes, such as melting or solidification, remains inadequately understood\@. This investigation focuses on the melting process of NePCM in a square cavity, exploring distinct cases of melting from both the top and bottom sides. The NePCM comprises copper nanoparticles (2 nm in size) suspended in water. Our study involves different combinations of constant temperature boundary conditions and particle volume fractions\@. Utilizing a numerical model based on the one-fluid mixture approach combined with the single-domain enthalpy-porosity model, we account for the phase change process and particles' interaction with the solid-liquid interface. When melting NePCM from the top side, convection effects are suppressed, resulting in a melting process primarily governed by conduction. Both NePCM and pure water melt at the same rate under these conditions. However, melting NePCM from the bottom side induces convection-dominated melting. For pure water, thermal convection leads to the formation of convection cells during melting. Contrastingly, melting NePCM triggers thermosolutal convection due to temperature and particle concentration gradients. The flow cells formed from thermosolutal convection in NePCM differ from those in pure water driven by pure thermal convection. Our simulations reveal that thermosolutal convection contributes to decelerating the solid-liquid interface, thereby prolonging NePCM melting compared to pure water. Surprisingly, the viscosity increase in NePCM plays a minimal role in the deceleration process, contrary to prior literature attributing slow-downs of the melting process of the NePCM primarily to increased viscosity.