Modeling and analysis of heat transfer and fluid flow mechanisms in nanofluid filled enclosures irradiated from below

Radiation-driven transport mechanisms are ubiquitous in many natural flows and industrial processes. To mimic and to better understand these processes, recently, radiatively heated nanofluid filled enclosures have been extensively researched. The present work is essentially a determining step in quantifying and understanding the transport mechanisms involved in such enclosures. In particular, a two-dimensional square nanofluid filled enclosure irradiated from the bottom has been investigated in laminar flow situation. Effects of nanofluid optical depth, inclination angle of the enclosure, incident flux, and boundary conditions (adiabatic and isothermal) have been investigated. Moreover, the temperature and flow fields have been carefully analyzed in the situation ranging from "volumetric " to "mixed " to "surface " absorption modes. Under adiabatic boundary conditions, steady state is unconditionally achieved irrespective of the incident flux magnitude (varied between 5 W m-2 -50 W m-2), enclosure inclination angle (varied between 0 to 60) and mode of absorption (surface, mixed or volumetric). However, in case of isothermal boundaries; onset of natural convection and its transition into transient regime is significantly impacted by the mode of absorption and the enclosure inclination angle.