Inward melting inside a horizontal multilobed capsule with conductive wall affected by Ag-MgO/water hybrid and MgO/water nanofluids

We scrutinize the possibility of boosting the functionality of an isothermally heated horizontal capsule filled with the phase change material (PCM) as the thermal energy storage (TES) system. There is the conjugate heat transfer at the wall. The constrained inward melting of the water/ice (Pr=6.2) at Ra=105 in this system should be improved since the thermal conductivity of the base PCM is low. The thermal performance of the PCM may be manipulated by adding the magnesia (MgO) and hybrid Ag/MgO nanoparticles and by using the multilobed capsules. The iterative explicit lattice Boltzmann method (LBM) is implemented to investigate the effects of the nanoparticle loading, aspect ratio (AR) and circumference of the cross-section on the full melting time. The use of the 2-lobe capsule with the highest AR and increased circumference reduces the full melting time by 37% in contrast to the pure PCM melting in the cylindrical tube. Using the MgO nanoparticles with a lower loading (0.01) within the 2-lobe capsule diminishes the complete melting time for the pure PCM by 55%. It is the best nanofluid-based case when we consider the price of nanoparticles and the capacity of the TES system. The hybrid nanoparticles/PCM composites with (50:50) weight proportions are not prescribed as the increment of the viscosity of the PCM is further than that of the thermal conductivity of the PCM. To decrease the thermal conduction resistance at the bottom section of the horizontal cylindrical capsule, it is suggested to use the multilobed capsule for the pure PCM melting instead of the expensive single nanoparticles.