Concrete is tested as a sensible heat thermal energy storage (TES) material in the temperature range of 400–500 °C (752–932 °F). A molten nitrate salt is used as the heat transfer fluid (HTF); the HTF is circulated though stainless steel heat exchangers, imbedded in concrete test prisms, to charge the TES system. During charging, significant cracking occurs in both the radial and longitudinal directions in the concrete prisms. The cracking is due to hoop stress induced by the dissimilar thermal strain rates of concrete and stainless steel. A 2D finite element model (FEM) is developed and used to study the stress at the prism/exchanger interface. Polytetrafluoroethylene (PTFE) and a heat-curing, fibered paste (HCFP) are tested as interface materials to mitigate the stress in the concrete. Significant reduction in the size and number of cracks is observed after incorporating interface materials. A heat exchanger with a helical fin configuration is incorporated to improve the heat transfer rate in the concrete. Testing confirms that the fins increase the rate of heat transfer in the concrete; however, large cracks form at each of the fin locations. Only the HCFP is tested as an interface material for the finned heat exchanger. The HCFP decreases the number and size of the cracks, however, not to the desired hairline levels.

The analysis on heat transmission and fluid flow characteristics within the cavity is useful to improve the features of several applications including energy storage devices and hybrid fuel cells. With this motivation, the present model investigates the characteristics of magneto-convective heat transmission and fluid flow within a square porous enclosure with hot and cold slits. The heat transfer features of electrically conducting hybrid nanofluids Fe₃O₄-MWCNT-water and Fe₃O₄-MWCNT-kerosene is analyzed inside the enclosure. The non-Fourier thermal flux model is deployed and the internal heat absorption/generation effect is considered. The Marker-And-Cell (MAC) numerical scheme is adopted to solve the transformed dimensionless mathematical model with associated initial-boundary conditions. An exhaustive parametric investigation is implemented to estimate the influence of key parameters on the transport phenomena. The computations show that augmenting the Hartmann number values modify the fluid flow and temperature features substantially for both the hybrid nanofluids. Enhancing the values of nanoparticles volume fraction promotes the heat transfer. When 5% Fe₃O₄-MWCNT nanoparticles are suspended into water and kerosene base fluids, Fe₃O₄-MWCNT-kerosene hybrid nanofluid achieves 6.85% higher mean heat transfer rate compared to Fe₃O₄-MWCNT-water hybrid nanoliquid. In the existence of heat absorption, the mean rate of heat transfer of Fe₃O₄-MWCNT-water hybrid nanofluid is 78.92% lower than Fe₃O₄-MWCNT-kerosene hybrid nanoliquid. Greater energy transmission is noticed in the case of Fe₃O₄-MWCNT-kerosene hybrid nanofluid and the enhanced fluid flow is noticed in the case of Fe₃ O₄-MWCNT-water hybrid nanofluid. Fourier's model (δ_e=0) estimates higher heat transfer rate than that of the Cattaneo-Christov (non-Fourier) heat flux model (δ_e≠0).