The impact of thermosolutal convection on melting dynamics of Nano-enhanced Phase Change Materials (NePCM)

Journal article (2024)

Authors

Yousef M.F. El Hasadi Complex Fluid Processing - Mechanical, Maritime and Materials Engineering , Offshore Engineering - CEG , Eindhoven University of Technology
Research Group
Complex Fluid Processing (Mechanical, Maritime and Materials Engineering) (TU Delft)
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Published Date

2024

Language

English

Faculty

Mechanical, Maritime and Materials Engineering

Department

Process and Energy

Research Group

Complex Fluid Processing

Abstract

Nanoparticle-Enhanced Phase Change Materials (NePCM) have garnered significant attention in engineering literature due to their enhanced thermo-physical properties. However, their behavior during phase change process, such as melting or solidification, remains inadequately understood. This study focuses on investigating the melting process of NePCM in a square cavity, exploring distinct cases of melting from both the top and bottom sides. Notably, this work delves into the effect of thermosolutal convection on NePCM melting for the first time in the literature. The NePCM comprises copper nanoparticles (2 nm in size) suspended in water. We examine various combinations of constant temperature boundary conditions and particle volume fractions. Employing a numerical model based on the one-fluid mixture approach combined with the single-domain enthalpy-porosity model, we capture the phase change process and particles’ interaction with the solid–liquid interface. In our investigation, the hot side temperature ranges between 290 K and 300 K, while the cold side temperature remains fixed at 270 K. The mass fraction of particles (ϕw) varies from 0.5% to 10%. 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. In the case of pure water, thermal convection leads to the formation of convection cells during melting. In contrast, 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. For example, for a mass fraction of particles (ϕw = 10%), NePCM melts 6% slower compared to pure water. Surprisingly, the increase in viscosity of NePCM plays a minimal role in the deceleration process, contrary to prior literature attributing slowdowns of the NePCM melting process primarily to increased viscosity.