Impact of Oscillatory Conditions on Thermal Enhancement in Nanofluid Flow Through Porous Media

With growing demands for thermal management in the modern systems of engineering, increase in heat transfer in porous structures has become one of the key areas of research priorities. The nanofluids, which are developed by dispersing nanoscale particles of solids in the existing base fluids, have shown better thermal conductivity than the old-fashioned heat transfer fluids. In such nanofluids under oscillatory conditions, complex interactions between fluid inertia, permeability resistance and temporally varying forcing mechanisms occur when they flow through porous media. Then the knowledge of such interactions is absolutely necessary in the optimization of thermal systems with either periodic or pulsating flow conditions. The present study investigates the effect of the oscillatory boundary conditions on the thermal enhancement in a porous media nanofluid flow. The model to be used is a two-dimensional porous channel, and the equations governing the model the continuity equation, the full two-dimensional Brinkman-extended Darcy momentum equations and the energy equation are generated. In order to model pulsatile flow, an oscillatory velocity profile is prescribed at the boundary. Unless stated otherwise, the base fluid is water and the nanoparticle phase is copper (Cu). The equations so obtained are non-dimensionalized and resolved numerically through a finite-difference approach. The effect of the frequency of oscillation, Darcy number, and the volume fraction of the nanoparticles on temperature distribution and the Nusselt number are then examined, including their combined/interaction effects. These results indicate that compared with steady flow conditions, oscillatory flow increases the convective heat transfer by a large percentage up to 39.6% at Ω = 3.0, 37.1% at φ = 0.06, and 40.8% at Da = 0.10 relative to the steady, non-oscillatory baseline. The higher the oscillation frequency, the better the thermal boundary layer mixing and hence the higher the Nusselt numbers. Further, at higher volume fractions of nanoparticles, the thermal conductivity enhancement is also observed, leading to measurable heat transfer enhancement. The results are applicable to energy conversion equipment, nuclear thermal management, electronic climate coolers and miniature heat exchangers.