NUMERICAL INVESTIGATION OF TURBULENT NANOFLUID FLOW AND TWO-DIMENSIONAL FORCED-CONVECTION HEAT TRANSFER IN A SINUSOIDAL CONVERGING-DIVERGING CHANNEL

The purpose of this research is to numerically simulate turbulent flow and forced-convection heat transfer of a water/CuO nanofluid in a sinusoidal converging-diverging channel. In the present study, the effects of some parameters such as Reynolds number in the range 4000 <= Re <= 20,000, volume fraction of nanoparticles in the range 1% <= phi <= 4%, and the wavelength in the range 0.2 m <= lambda <= 1 m on velocity, temperature, and pressure contours, Nusselt number, friction factor, and also the velocity and temperature profiles in various cross sections of the channel have been investigated. The simulations were done by the finite volume method in a 2D space in Cartesian coordinates. The obtained results indicate that on increase of the volume fraction of solid nanoparticles with the use of wavy walls, the heat transfer rate rises significantly. The presence of sinusoidal walls compared with flat ones is accompanied by a higher friction factor and pressure drop. By increasing the Reynolds number, the axial velocity of flow increases 5 times, the Nusselt number increases by 94%, and the friction factor reduces by almost 2.5 times. By increasing the wavelength from 0.2 to 1 m, the heat transfer area is reduced and the conduction heat transfer coefficient is reduced due to the reduced flow velocity and temperature gradient on the channel walls as the thickness of the velocity and thermal boundary layers rises resulting in reduced Nusselt number and heat transfer rate. Based on the contours of the axial flow velocity at the end of the converging section of the channel, the flow distribution is no longer uniform and the flow velocity is continuously changing and at the center of the channel (channel neck), when the volume fraction is raised from 1 to 4%, the flow velocity increased by 25%. By increasing the wavelength of the wall, the axial velocity of flow and Nusselt number are reduced by almost 85% and 91%, respectively. Also, by increasing the volume fraction of nanoparticles, the axial velocity of flow and Nusselt number are increased nominally.