Entropy generation analysis on MHD mixed convective flow of couple stress MWCNT-Ag/C2H6O2 hybrid nanofluid with variable properties in a vertical channel

The investigation of the mixed convective magnetohydrodynamic (MHD) flow of a couple stress hybrid nanofluid having temperature-dependent viscosity and thermal conductivity in a vertical channel is dealt with within this paper. The considered hybrid nanofluid is processed by mixing multiwalled carbon nanotubes (MWCNT) and silver (Ag) nanoparticles in a base fluid of ethylene glycol (C2H6O2) assuming the base fluid and the nanoparticles to be in a thermal equilibrium state following the Tiwari-Das nanofluid model. The flow is generated by the buoyancy force under the standard Boussinesq approximation and the pressure gradient force. The effect of a uniform transverse magnetic field is considered, and a constant temperature is maintained at the channel walls. The governing momentum and energy equations are nondimensionalized with relevant dimensionless parameters and solved using the homotopy analysis method (HAM) to obtain semi-analytical solutions. The skin friction coefficient and Nusselt number on the channel walls are derived to analyze the shear stress and heat transfer rate, and to scrutinize the irreversibilities in the system, the entropy generation number and the Bejan number are defined. The emphasis is given to the analysis of velocity and temperature profiles, irreversibilities in the system, shear stresses, and heat transfer rate on the channel walls concerning the volumetric concentration of the nanoparticles, shape factor effect for various nanoparticle shapes, and temperature-dependent viscosity and thermal conductivity. The analysis reveals that with higher shape factors and enhancement of nanoparticle concentration, both velocity and temperature degrade, and the entropy generation rate escalates with growing heat transfer irreversibility. Moreover, a lower and higher shear stress and heat transfer rate are achieved, respectively. The variable viscosity and thermal conductivity parameters effectively alter the velocity and temperature profiles, irreversibilities, shear stress, and heat transfer rate.