Mixed convection of nanofluid flow in a circular lid-driven cavity affected by attack angle changes: A numerical simulation

Cavities are one of the most widely used passive tools in microscale cooling. In this numerical research, the flow and mixed convection heat transfer of water/Ag nanofluid in a circular cavity is simulated. In this research, by choosing a circular cavity geometry, with the presence of hot and cold sources affected by changes in the angle of attack and the linear motion of the cold source, the behavior of nanofluid flow and heat transfer is investigated. Different nanoparticle volume fractions (φ), Richardson numbers (Ri), and cavity attack angles are studied. This research aims to explore the simultaneous effect of changes in φ and the position of a circular lid-driven cavity. The behavior of the nanofluid is investigated and simulated in a single-phase manner. Second-order and Upwind SIMPLEC algorithms are used to solve the flow governing equations. Radiation effects are ignored. The results show that due to the no-slip boundary condition, increasing the lid velocity causes the velocity boundary layer to penetrate and stimulate the entire flow field. Moreover, the placement of hot and cold surfaces can also affect fluid movement. If the created temperature gradients are in agreement, the movement of the current will intensify. At Ri = 1, due to the stronger stimulation of the flow field and increased circulation caused by fluid movement, the flow velocity components have become stronger. The flow distribution in the cavity is done with a higher intensity, and stronger vortices are formed. Due to the slow motion of the lid at Ri = 10, part of the heat transfer between the fluid layers can be done by the conduction mechanism. Combined convection is slow, and the formation of the thermal boundary layer is recognizable. The movement of fluid in this cavity depends on its placement. This depends on the changes and direction of flow in the boundary between hot and cold sources. By increasing φ, the density and viscosity of the nanofluid also increase, which can improve heat transfer. A higher φ can increase the Nusselt number (Nu), which, of course, depends on the location of the hot and cold surfaces.