Melting dynamics and specific energy storage of metal foam supported paraffin in multi-tube heat exchangers: Role of shell-tube geometry, hybrid nanoparticle, and a novel index

Abstract

One of the methods used to improve the low performance caused by the low thermal conductivity of phase change materials (PCMs) in latent heat thermal energy storage (LHTES) systems is to subject the system to geometric modification. In this context, numerical analysis of different geometric variations (for shell: circular, hexagonal, and triangle; for tube: triangle, hexagonal, and elliptical) were carried out in LHTES systems obtained from conventional multi-tube heat exchangers with circular shell and tube geometries (C-Circle). The geometries were defined as organic RT35HC PCM and aluminum metal foam (MF) with porosity and pore density of epsilon = 0.90 and omega = 20 PPI, respectively. The governing equations were solved by the Darcy-Brinkman-Forchheimer model, and the enthalpy-porosity approximation was used during the melting process of the PCM. In addition, hybrid nano PCM (HyNPCM) with phi = 2.0% and 6.0% was obtained by mixing graphene oxide (GO) + MXene nanoparticles with equal volume concentration (phi) into the PCM, and their melting and energy storage performances were investigated. The results showed that the H-Elliptical has the shortest melting time. The melting times of the phi = 6.0% HyNPCM+MF were 1.2% and 2% shorter than those of the phi = 2.0% HyNPCM+MF and pure PCM+MF, respectively. However, increasing rp negatively affected the amount of stored energy, and the energy stored in the pure PCM+MF was approximately 8.0% higher than that of the phi = 6.0% HyNPCM+MF. In comparison with the C-Circle, the H-Elliptical reached full melting at t = 49 s earlier, and the energy stored in this state was approximately 0.7% higher. It was also determined that the H-Elliptical could supply 0.04 L m(-1) more domestic hot water than the C-Circle when water is passed through the tube. Furthermore, to clearly determine the positive impact of the applied performance improvement techniques on melting time and the negative impact on the amount of energy stored, the use of the new dimensionless Storage Performance Parameter (SPP), which is not available in the literature, was proposed.