Natural convection of nanoparticle–water mixture near its density inversion in a rectangular enclosure

Natural convection of mixture of nanoparticles and water near its density maximum in a rectangular enclosure is studied numerically. A non-Boussinesq homogenous model is used in mathematical formulations of governing equations. The finite volume method is used to solve the governing equations. The results are presented graphically in the form of streamlines, isotherms and velocity vectors and are discussed for various nanoparticle volume fractions. It is observed that flow and temperature field is affected significantly in the presence of nanoparticles. The average heat transfer rate considering a non-Boussinesq temperature-dependent density (inversion of density) is lower than considering a Boussinesq temperature-dependent density. The average Nusselt number increases with an increase of nanoparticle volume fraction. It is observed that the density inversion of water leaves strong effects on fluid flow and heat transfer due to the formation of bi-cellular structure. The properties of nanoparticles also affect the fluid flow and heat transfer.