Abstract
Thermal storage system (TES) with phase change material (PCM) is an important device to store thermal energy. It works as a thermal buffer to reconcile the supply energy with the energy demand. It has a wide application field, especially for solar thermal energy storage. The main drawback is the low value of thermal conductivity of the PCM making the system useless for thermal engineering applications. A way to resolve this problem is to combine the PCM with a highly conductive material like metal foam and/or nanoparticles. In this paper a numerical investigation on the metal foam effects in a latent heat thermal energy storage system, based on a phase change material with nanoparticles (nano-PCM), is accomplished. The modelled TES is a typical 70 L water tank filled with nano-PCM with pipes to transfer thermal energy from a fluid to the nano-PCM. The PCM is a pure paraffin wax and the nanoparticles are in aluminum oxide. The metal foam is made of aluminum with assigned values of porosity. The enthalpy-porosity theory is employed to simulate the phase change of the nano-PCM and the metal foam is modelled as a porous media. Numerical simulations are carried out using the Ansys Fluent code. The results are shown in terms of melting time, temperature at varying of time, and total amount of stored energy.
Highlights
Thermal Energy Storage (TES) [1] is a device capable of storing excess energy by heating a storage medium
The results have shown that metal foam is more effective with respect to the nanoparticles for the improvement of the phase change material (PCM) melting rate
V is the velocity of the fluid phase (PCM or nano-PCM), ε is the porosity of the metal foam, t is the time, μ is the dynamic viscosity of the fluid phase, p the relative pressure, and S is a source term expressed in Equation (8)
Summary
Thermal Energy Storage (TES) [1] is a device capable of storing excess energy by heating a storage medium. There are many types of PCM in literature [3], in particular, for a solid-liquid phase change process, paraffin [4] has many advantages such as high latent heat, non-toxicity, chemical stability, and small volume variation, but one of the worst drawbacks is the low value of thermal conductivity, making the application of pure PCM counterproductive for thermal storage application because it could behave as an insulated material. Siahpush [12] have performed both a numerical and experimental study on a thermal energy storage system with PCM and metal foam, assuming the local thermal equilibrium hypothesis to simulate the heat transfer between PCM and metal foam. Tian and Zhao [13] have numerically investigated a TES system with paraffin RT58 as the PCM with aluminum metal foam assuming the local thermal non-equilibrium model. The charging process is monitored in terms of liquid fraction, average temperature evolution, and stored energy
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