Numerical study of pulsatile MHD counter-current nanofluid flows through two elastic coaxial pipes containing porous blocks

We investigate the MHD convective pulsatile flow through a counter-current two-nanofluid (Cu-water and CuO-water) system. This system consists of two elastic coaxial pipes, with porous blocks mounted on the walls of each channel. Hot CuO-water nanofluid flows upwards in the inner channel, while cold Cu-water nanofluid flows downwards in the outer channel. A two-phase model that considers the effects of thermophoresis and brownian motion on the concentration of nanoparticles within the fluid is used to describe heat and mass transfer within the system. The governing equations with the associated initial and boundary conditions are solved using the mixed finite element method with P-2 - P-1 Taylor-Hood elements. The influence of time, pulsation frequencies and amplitudes of the inner and outer fluids, elastic modulus, Reynolds number, solid volume fractions of the inner and outer nanofluids, and the diameters of the Cu and CuO nanoparticles on fluid flow, heat transfer, nanoparticle concentration and pressure drop is studied. We found that heat transfer may be enhanced by increasing parameters such as the elastic modulus of the pipes, Reynolds number, solid volume fraction of nanoparticles in the inner fluid and nanoparticle size in the outer fluid. Similarly, heat transfer is enhanced by reducing the solid volume fraction of nanoparticles in the outer fluid and nanoparticle size in the inner fluid. In most cases, the heat transfer enhancement observed in the study is accompanied by increases in pressure drop. (C) 2017 Elsevier Ltd. All rights reserved.