- Two macroscopically solid, PCM enhanced thermal storage materials were developed.
- The materials have significant energy density; 0.96 MJ/L and 1.1 MJ/L respectively.
- Thermal conductivity is two orders of magnitude greater than conventional materials.
- The phase change temperatures, 577 °C and 660 °C, suit steam turbine operation.
- Short-term thermal cycling supported material stability in the operating range.
A metastable miscibility gap in the C-Al binary phase diagram has been exploited to produce macroscopically solid phase-change enhanced thermal energy storage materials.
With 50% by volume of Al or Al-12.7%Si dispersed in a graphite matrix, the materials have thermal conductivity of ∼150 W/m K, energy densities of 0.9 and 1.1 MJ/L for ΔT = 100 °C and energy storage/delivery temperatures centred around 660 °C and 577 °C respectively.
These characteristics are matched to both direct-steam and fluid-mediated concentrated solar thermal power systems using conventional Rankine cycle steam turbine-generator technology.
Powder metallurgy processing combined with a low-temperature binder ensures a non-percolating inverse microstructure in which the phase change Al or Al-Si particles are securely encapsulated, thereby overcoming the usual containment problems associated with metallic phase change materials.
The graphite and binder system used have been shown to be stable upon short-term thermal cycling or holding at the maximum expected operating temperature.