Nanofluid filled enclosures: potential photo-thermal energy conversion and sensible heat storage devices

In the present work we propose "nanofluid filled enclosures" as potential photo-thermal energy conversion and sensible heat storage devices. Herein, the optical charging of the nanofluid has been modeled as "solar radiant energy - nanoparticles" interaction. The subsequent energy redistribution has been modeled as coupled transport phenomena involving mass, momentum and energy transport. In particular, nanofluid filled enclosure with adiabatic, and isothermal (through convective) boundaries have been analyzed to decipher the fundamental limits of sensible heat storage and thermal discharging capacities respectively. Furthermore, the effect of nanoparticles volume fraction on the photo-thermal energy conversion mechanisms and its redistribution thereof has been critically investigated. Detailed analysis reveals that under similar operating conditions, in volumetric absorption mode (i.e., at low nanoparticles volume fraction) nanofluid filled enclosure has higher sensible heat storage (8%-20% higher) and thermal discharging (13%-58% higher) capacities than in the corresponding surface absorption mode (i.e., at high nanoparticles volume fraction). Overall, "nanofluid filled enclosures", particularly in volumetric absorption mode, could be deployed for efficient solar thermal conversion and storage.