Linear stability perspective on mixed convection flow of nanofluids in a differentially heated vertical channel

We report instability properties of mixed convection flow of different nanofluids in a differentially heated vertical channel through a linear stability analysis. A single-phase nanofluid model is used to report the instability mechanism of nanofluids, which fairly works for the low concentration of the nanoparticles. The stability results are examined for five different types of water-based nanofluids. The basic flow and linear disturbance equations are solved with the Chebyshev spectral collocation method. The influence of nanoparticles volume fraction (phi) in different water-based nanofluids is analyzed in terms of growth rate analysis, instability boundaries and kinetic energy analysis. The results reveal that increasing the concentration of nanoparticles in the water improves the stability of the basic flow. However, increasing the Reynolds number (Re) value destabilizes the basic flow of nanofluid due to the dominant nature of the shear force. Compared to conventional pure water fluid, the inclusion of nanoparticles in pure water delays the onset of instabilities by reducing the growth of the disturbance. The order of stability for different nanofluids in (phi, Gr/Re)-plane is observed as: Al2O3/water > TiO2/water > CuO/water > Cu/water > Ag/water nanofluid, where Gr is Grashof number. By increasing the volume percentage of nanoparticles, the friction coefficient at the heated wall of the channel decreases. The kinetic energy balance at the critical level shows that shear instability is the most dominant instability for considered nanofluids.