Numerical study of periodic natural convection in a nanofluid-filled enclosure due to transitional temperature of heat source

A numerical study of unsteady periodic natural convection flows through an alumina–water nanofluid in a square cavity due to a sinusoidal time-dependent temperature of a thin heat source located at the center of the enclosure is performed. It is found that an oscillating time-dependent temperature of the heat source cased to create a periodic variation in the fluid flow and temperature field in the cavity after certain time duration. The influence of the nanoparticle on the flow and temperature fields have been plotted and discussed. It is observed that the average Nusselt number is an increasing function of nanoparticle volume fraction and Rayleigh number for all the oscillation periods and Rayleigh numbers investigated. It is also found that the performance of the nanoparticle utilization on the enhancement of the heat transfer at higher Rayleigh numbers (Ra = 106) is less than that of lower Rayleigh numbers (Ra = 103).