Numerical modelling of phase change material melting process embedded in porous media: Effect of heat storage size

Abstract

The aim of this paper is to study the influence of enclosure size in latent heat thermal energy storage systems embedded in a porous medium for domestic usage of latent heat thermal energy storage heat exchangers. A 2-D rectangular enclosure is considered as the computational domain to study the heat transfer improvement for a phase change material embedded in a copper foam considering a constant heat flux from the bottom surface. Different dimensions of the composite system are examined compared with a system without a porous medium. The thermal non-equilibrium model with enthalpy-porosity method is employed for the effects of porous medium and phase change in the governing equations, respectively. The phase change material liquid fraction, temperature, velocity, stream lines and the rate of heat transfer are studied. The presence of a porous medium increases the heat transfer significantly, but the improvement in melting performance is strongly related to the system's dimensions. For the dimensions of 200 × 100 mm (W × H), the melting time of porous-phase change material with the porosity of 95% is reduced by 17% compared with phase change material-only system. For the same storage volume and total amount of thermal energy added, the melting time is lower for the system with a lower height, especially for the phase change material-only system due to a higher area of the input heat. The non-dimensional analysis results in curve-fitting correlations between the liquid fraction and Fo.Ste.Ra −0.02 for rectangular latent heat thermal energy storage systems for both phase change material-only and composite-phase change material systems within the parameter range of 1.16 < Ste < 37.13, 0 < Fo < 1.5, 2.9 × 104 < Ra < 9.5 × 108, 0 < L f < 1 and 0 < Fo.Ste.Ra −0.02 < 0.57. Over a range of system's volume, heat flux and surface area of the input heat flux, the benefit of composite phase change material is variable and, in some cases, is negligible compared with the phase change material-only system.

Optimum Placement of Heating Tubes in a Multi-Tube Latent Heat Thermal Energy Storage

“…According to the enthalpy-porosity method [ 34 , 35 ], the conservation equations of continuity, momentum, and energy are given considering the following assumptions, i.e., laminar and Newtonian fluid flow for the molten PCM as well as neglecting the viscous dissipation and volume expansion of the PCM during the phase change process. The variation of density is negligible except for the buoyancy force, which is modeled considering the Boussinesq approximation.…”

Effect of airflow channel arrangement on the discharge of a composite metal foam‐phase change material heat exchanger

“…This shall confirm the good validity and reliability of the current model for predicting of the solidification behavior of the PCM‐foam system under consideration. Note that the thermal equilibrium model is adopted in this study due to the high computational cost of the thermal non‐equilibrium model in 3D simulations and small variation between the employed thermal non‐equilibrium and equilibrium models as presented in authors' previous work 55 …”

Phase Change Process in a Zigzag Plate Latent Heat Storage System during Melting and Solidification

“…Because of the low velocity, the viscous dissipation is neglected and the Boussinesq approximation applied to density and buoyant force. The outer wall of the tube is assumed to be well insulated with no heat loss to the ambient [ 61 ]. The velocity and temperature in the z-direction are constant and, therefore, the 2-dimensional geometry is assumed [ 42 ].…”

“…The conservation equations governed on the phase change problem, including the mass, momentum and energy (Equations (1)–(3), respectively) equations are given briefly as follows based on the enthalpy–porosity method introduced by Brent et al [ 61 ]. This method utilized due to its ability to solve explicit tracking of the solid–liquid interface as well as providing a simple operation of phase-change problems [ 62 , 63 ]: where , t, V, P, , are density, time, velocity, pressure, viscosity and gravity acceleration, respectively.…”

“…In Equation (2), S is the momentum source term in the mushy zone based on the enthalpy–porosity approach, which takes the following form: where the term is the mushy zone constant reflecting the mushy zone morphology that illustrates how the velocity is reduced when the PCM solidifies. The constant is a small number to prevent division by zero when T solid is greater than T [ 61 , 64 , 65 ]. The following parameters were utilized in the present study: .…”