Abstract
Thermal energy storage units using macro-encapsulated PCM in industrial and residential applications are contemporary due to better efficiency during charging and discharging. This article focuses on numerical modelling of the melting process in a macro-encapsulated PCM. Accounting the non-linear enthalpy–temperature relation and ramping down the velocity in solid phase is therefore fundamental. In the present article the variable viscosity method is implemented to ramp down the solid velocity and allow settling of the solid phase. This complete numerical model of melting and settling of PCM in a capsule is implemented in OpenFOAM. The numerical results for different solid viscosities are validated with experiments and show good agreement. The influence of the solid viscosity value and the pressure–velocity convergence is studied. It is observed that the pressure–velocity convergence only plays a greater role in the case where the computation of the exact solid velocity is required.
Highlights
Statistics reveal that the global energy demand is set to grow by 37% until 2040 [1]
Macro-encapsulation of phase change material (PCM) may enhance the thermal distribution in thermal storage units by increasing the heat transfer area between the heat transfer fluid (HTF) and PCM
Different simplified approaches exist to analyse macro-encapsulated PCM but they are limited to specific applications and are less accurate in predicting the performance of thermal storage units
Summary
Statistics reveal that the global energy demand is set to grow by 37% until 2040 [1]. Different simplified approaches exist to analyse macro-encapsulated PCM but they are limited to specific applications and are less accurate in predicting the performance of thermal storage units. Asako et al [5], Assis et al [6] and Rösler [7] developed different CFD models to study the melting of a PCM with settling in a capsule. The Eulerian fixed grid approach is most common to model moving boundary interfaces for a solid–liquid phase change. Apart from modelling the non-linear enthalpy and temperature relationship ramping down velocity in the solid phase is required. Viscosity is generally associated with fluids but in this method the solid phase is proposed to have higher viscosity values. This article does discuss the implementation of VVM with solid settling and its convergence and influence on the melting rate
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