Instability and sensitivity analysis of streaming nanofluid-air interface

The nanofluid/air interface is practically used in enhancing heat transfer efficiency in thermal management systems, such as in cooling electronics and improving the performance of solar collectors. Additionally, it finds applications in advanced manufacturing processes and biomedical devices, where precise temperature control is crucial. The study investigates the instability of the interface between a Newtonian nanofluid and air in a rectangular setup. This instability arises when the two fluids flow at different velocities, leading to Kelvin-Helmholtz instability at the interface. The air is treated as a viscous, incompressible fluid due to its low Mach number, positioned above the nanofluid. The stability of the interface is determined based on the relative velocity of the fluid layers. The study reveals that various flow parameters, including viscosity ratio, density ratio, volume fraction, and nanoparticle diameter, influence the stability or instability of the interface. Four types of nanofluids are considered, and a comparative analysis is conducted. Interestingly, the nanofluid/air system is found to be more stable compared to the viscous liquid/air system. Sensitivity analysis is performed to examine the impact of different physical variables and their interactions on the critical relative velocity. It is observed that the critical velocity consistently exhibits positive sensitivity to the density ratio. Moreover, the magnitude of critical velocity sensitivities for the density ratio remains constant across all cases. The critical velocity demonstrates the highest positive sensitivity with respect to the parameter of air thickness, with this maximum sensitivity occurring when the air thickness equals 1 and the densities of both fluids are identical.