A Multi-functional Graphite/epoxy-based Thermal Energy Storage Composite for Temperature Control of Sensors and Electronics

A novel multi-functional plate-like lamination that combines a thermal energy storage capability with a structural capability is described. The lamination consists of a paraffin impregnated porous graphitic core (the energy storage volume) encapsulated between rigid graphite/epoxy composite skins. Heat storage is via solid-liquid phase transition of the paraffin. Stacked laminations form a sandwich structure. A thermal response model shows that the graphite foam is an effective thermal conductivity enhancer to the imbedded paraffin. It will effectively immobilize liquid paraffin so that the thermal storage process will be unaffected by up to a 10g load. Furthermore, the foam can accommodate the relatively large specific volume change that accompanies paraffin phase transition. However, it does so at the expense of reduced thermal performance. Structural analysis shows that graphitic foam has a low strength and elasticity modulus, and the material displays tension-compression asymmetry. The paraffin fill is shown to increase the compressive ultimate strength and elasticity modulus. The use of carbon fiber/epoxy skin greatly enhances the overall strength of the structure. Nomenclature A Area B Eq. (14b) C, D Eqs. (14) d Diameter E Modulus h Latent heat I,K Bessel functions k Thermal Conductivity n Number of sub-laminations P Pitch q Heat Transfer Rate q” Heat Flux r Radius Rk Eq. (7) s,t Thickness T Temperature V Volume α Specific surface area