Scrutinization of unsteady MHD fluid flow and entropy generation: Hybrid nanofluid model

The goal of the present paper is to scrutinize the heat transport of an unsteady stagnation-point flow of a hybrid nanofluid over a stretching/shrinking disk in the presence of a variable magnetic field and thermal radiation. The entropy generation analysis for the system is also made. The suitable similarity transformation is utilized for the reduction of a set of governing equations which are solved numerically by using fourth order Runge–Kutta procedure with shooting technique. The impact of different physical parameters under the realistic passive control of nanoparticles on the flow, heat transfer and concentration profiles are analyzed and demonstrated graphically. The analysis of the results obtained shows that multiple solutions exist for a certain parametric domain. With the increase in magnetic parameter ($M$), fluid velocity is found to increase for the first solution whereas opposite behavior is observed for the second solution. Also as $M$ increases, the temperature at a point decreases for the first solution branch. Further, the influences of Reynolds number, Brinkmann number and volumetric concentrations on entropy generation are sketched and discussed. The novel result that emerges from the analysis is that among two solution branches, the first solution branch is linearly stable and physically meaningful whereas the second solution branch is linearly unstable and cannot be realized physically.