  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
(7% - 27% higher) and thermal discharging (16% - 47% 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.
