Second law analysis for flow of a nanofluid containing graphene-platinum nanoparticles in a minichannel enhanced with chaotic twisted perturbations

The second law and entropy generation characteristics of a new hybrid nanofluid containing graphene nanoplatelets decorated with platinum nanoparticles are evaluated in a chaotic twisted channel. Although several investigations have been carried out on flows inside chaotic channels in the relevant literature, very few studies have employed nanofluids as working fluids in such configurations. The geometrical perturbations cause formation of counter rotating Dean roll-cells which intensify mixing in the flow and disturb the boundary layer. The intensity of perturbations considerably enhances at higher Dean numbers. The maximum velocity is shifted toward the outer wall due to the centrifugal force, and the maximum frictional entropy generation occurs there. Because the roll-cells lead to more uniform temperature distribution, thermal entropy generation reduces with increase of distance from the inlet of each bend. Moreover, by increasing concentration and Dean number, thermal entropy generation and Bejan number decrease while frictional entropy generation intensifies, however, due to dominance of thermal entropy generation, overall irreversibility of the nanofluid flow reduces. Besides, the temperature gradients become greater at higher wall heat fluxes which lead to the more intense thermal entropy generation. In addition, the difference between the Bejan numbers related to different wall heat fluxes is more noticeable at higher concentrations. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.