Improving Thermal Energy Storage with Modular Flat Plates and Wedge Fins
Making thermal storage faster and more practical
Latent heat thermal energy storage (LHTES) can store large amounts of heat within a compact volume by using phase change materials (PCMs). This makes it relevant to solar heating, building energy systems, waste-heat recovery and other applications where energy needs to be stored and released at a controlled temperature.
A key limitation, however, is heat transfer. Many PCMs have relatively low thermal conductivity, which can make charging and discharging too slow for practical operation.
A recent Mansim R&D contribution published in the Journal of Energy Storage investigates a modular flat-plate LHTES system designed to address this problem using wedge-shaped copper fins.
A modular flat-plate storage concept
The proposed system consists of repeatable PCM storage modules with heat-transfer-fluid channels running between them. Copper structures form the channel surfaces and extend into the PCM as tapered wedge fins, creating conductive pathways deeper into the storage material.
The modular configuration is particularly interesting for applications where storage capacity needs to be expanded by stacking repeated units.
Rather than modelling an entire storage assembly, the study developed a representative two-dimensional periodic cell. Periodic boundary conditions were used to reproduce the thermal interaction between neighbouring modules, substantially simplifying the computational problem while retaining the behaviour of an interior section of the storage stack.
Simulating melting and solidification
The numerical model used the finite element method together with an enthalpy-porosity formulation to simulate both melting and solidification of paraffin PCM.
A total of 26 cases were investigated, examining the effects of fin-height ratio, HTF-side tooth geometry, fin position, convective heat-transfer coefficient and periodic versus insulated boundaries.
The simulations tracked melt volume fraction, temperature distribution, natural convection and the movement of the phase-change front. Charging and discharging power were also calculated to assess how quickly thermal energy could actually be stored and recovered.
This distinction is important. The geometry that performs well during melting does not necessarily behave in the same way during solidification, because the dominant heat-transfer mechanisms change as the PCM transitions between solid and liquid states.
Study Findings
Fin geometry had a significant influence on storage performance.
A balanced fin-height ratio of 0.5 gave the shortest melting time among the tested ratios, performing around 8% better than the more extreme fin distributions. Increasing the tooth aspect ratio from 0.75 to 1.5 reduced melting time by 39% and nearly halved solidification time.
Fin location also mattered. At matched tooth ratios, top-fin configurations reduced melting time by approximately 12.5–26.2% compared with bottom-only configurations.
The heat-transfer conditions on the fluid side had an even stronger effect. Increasing the convective heat-transfer coefficient from 50 to 150 W/m²K reduced melting time by 44.9%. For the same geometry, average charging power increased from approximately 0.060 to 0.112 kW/m, while average discharging power increased from 0.055 to 0.086 kW/m.
The importance of the fins becomes especially clear when compared with the finless reference case. The best-performing evaluated case reduced melting time by around 76.6% compared with the finless insulated configuration.
Mansim R&D: understanding the physics behind storage performance
The study highlights why thermal storage design cannot be reduced to PCM selection alone. Geometry, conductive pathways, natural convection and heat-transfer boundary conditions all influence how effectively the stored energy can be accessed.
During melting, natural convection becomes increasingly important as the liquid region develops. During solidification, convection gradually weakens and conduction through the fins becomes more important for removing heat from the remaining liquid PCM.
For Mansim R&D, this work reflects a wider approach to thermal engineering: using advanced numerical modelling to understand the physical mechanisms behind system performance and identify practical design improvements.
As thermal storage becomes increasingly important for renewable energy, building heating and industrial heat recovery, improving the rate at which energy can be stored and recovered will be just as important as increasing storage capacity itself.
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