Time Response of Natural Convection of Nanofluid CuO-H2O in Enclosure Submitted to a Sinusoidal Thermal Boundary Condition

A two-dimensional steady laminar natural convection in rectangular enclosure filled with CuO-water nanofluid is numerically investigated. The horizontal walls are thermally insulated and the left vertical side one is heated by a temporal sinusoidal temperature variation, whereas the right wall is kept at cold temperature. Mass Conservation, momentum, and energy equations are numerically solved by the finite volume element method using the SIMPLER algorithm for pressure-velocity coupling. This study has been carried out for four parameters: the volumetric fraction of nanoparticles  (0%≤ 4%), aspect ratio Ar (0.25≤Ar≤1), amplitude of temperature a (0.2≤a≤0.8) and its period (0.2≤Θ≤0.8). These simulations are performed at constant Rayleigh and Prandtl numbers (Ra=105and Pr=7.02). Numerical results show that the addition of nanoparticules into the basic fluid has a double role, increasing heat transfer and reducing the response time of the system. The decreasing of aspect ratio shows an increasing trend of the heat transfer and increases the amplitude of Nusselt number. We also see that after a time period the system does not return to its initial state (hysteresis phenomenon) because of the system inertia.