Entropy generation in steady MHD flow due to a rotating porous disk in a nanofluid

We consider the analysis of the second law of thermodynamics applied to an electrically conducting incompressible nanofluid fluid flowing over a porous rotating disk in the presence of an externally applied uniform vertical magnetic field. This study has applications in rotating magneto-hydrodynamic (MHD) energy generators for new space systems and also thermal conversion mechanisms for nuclear propulsion space vehicles. Von Karman transformations are employed to transform the governing equations into a system of nonlinear ordinary differential equations. The entropy generation equation is derived as a function of velocity and temperature gradient. This equation is non-dimensionalized using geometrical and physical flow field-dependent parameters. The velocity profiles in radial, tangential and axial directions, temperature distribution, averaged entropy generation number and Bejan number are obtained. A very good agreement is observed between the obtained results of the current study and those of previously published studies. The effects of physical flow parameters such as magnetic interaction parameter, suction parameter, nanoparticle volume fraction and the type of nanofluid on all fluid velocity components, temperature distribution, averaged entropy generation number and Bejan number, skin friction coefficient and Nusselt number are examined and analyzed and the path for optimizing the entropy is also proposed. In addition, this simulation represents the feasibility of using magnetic rotating disk drives in novel nuclear space propulsion engines and this model has important applications in heat transfer enhancement in renewable energy systems and industrial thermal management. (C) 2013 Elsevier Ltd. All rights reserved.